AN INTRODUCTION

                                TO THE

                            STUDY OF FISHES


                                  BY
                        ALBERT C. L. G. GÜNTHER
                        M.A. M.D. Ph.D. F.R.S.

       KEEPER OF THE ZOOLOGICAL DEPARTMENT IN THE BRITISH MUSEUM


  [Illustration: Carpit aquas pinnis.]


                               EDINBURGH
                        ADAM AND CHARLES BLACK
                                 1880

                       [_All rights reserved._]




               _Printed by_ R. & R. CLARK, _Edinburgh_.




                               PREFACE.


The scope of the present work is to give in a concise form an account
of the principal facts relating to the structure, classification, and
life-history of Fishes. It is intended to meet the requirements of
those who are desirous of studying the elements of Ichthyology; to
serve as a book of reference to zoologists generally; and, finally,
to supply those who, like travellers, have frequent opportunities
of observing fishes, with a ready means of obtaining information.
The article on “Ichthyology,” prepared by the late Sir J. Richardson
for the eighth edition of the “Encyclopædia Britannica,” is the only
publication which has hitherto partly satisfied such requirements;
and when I undertook, some years ago, to revise, or rather rewrite
that article for the new edition of that work, it occurred to me that
I might at the same time prepare a Handbook of Ichthyology, whilst
reserving for the article an abstract so condensed as to be adapted for
the wants of the general reader.

From the general plan of the work I have only departed in those
chapters which deal with the Geographical Distribution of Fishes. This
is a subject which has never before been treated in a general and
comprehensive manner, and seemed to demand particular attention. I
have, therefore, thought it right to give nominal lists of the Faunæ,
and the other details of fact on which I have based my conclusions,
although all the necessary materials may be found in my “Catalogue of
Fishes.”

A few references only to the numerous sources which were consulted
on the subjects of Chapters 1–12, are inserted in the text; more not
required by the beginner; he is introduced to a merely elementary
knowledge of facts well known to the advanced student.

With regard to the illustrations, about twenty have been prepared after
originals published by Cuvier, J. Müller, Owen, Traquair, Duméril,
Cunningham, Hasse, Poey, Siebold, and Gegenbaur. A similar number,
representing extinct fishes, have been taken, with the kind permission
of the author, from Owen’s “Palæontology.” My best thanks are due also
to the Committee of Publications of the Zoological Society, and to the
Editors of the “Annals and Magazine of Natural History,” and of the
“Journal des Museum Godeffroy,” for the loan of woodcuts illustrating
some of my papers on South American fishes and on larval forms. The
remainder of the illustrations (about three-fourths) are either
original figures, or formed part of the article on ‘Ichthyology’ in the
former edition of the “Encyclopædia Britannica.”

   LONDON, _3d October 1880_.




                               CONTENTS.


                         INTRODUCTORY REMARKS.

                                                                   PAGE

    FISH DEFINED--ICHTHYOLOGY DEFINED                                 1


                              CHAPTER I.

    HISTORY AND LITERATURE                                            2

    Aristotle, 2--Belon, 4--Salviani, 6--Rondelet, 6--Faunists and
    Anatomists of the Seventeenth Century, 7--Ray and Willughby,
    8--Artedi, 9--Linnæus, 10--Gronow and Klein, 12--Pupils
    and Successors of Linnæus, 12--Bloch, 13--Lacépède, 15--Anatomists
    and Faunists preceding Cuvier, 16--Cuvier, 17--Agassiz,
    20--J. Müller, 22--Discovery of Ceratodus, 25--Recent
    publications on Fishes, 26--Latest systematic works, 33.


                              CHAPTER II.

    TOPOGRAPHICAL DESCRIPTION OF THE EXTERNAL PARTS OF
      FISHES                                                         35

    Form of the body, 35--External parts of the head, 36--Trunk and
    Tail, 39--Fins; their structure, position, and function, 40--Skin
    and Scales, 45.


                             CHAPTER III.

    TERMINOLOGY AND TOPOGRAPHY OF THE SKELETON                       51

    Axial portion, 51--Vertebra and its parts; terms defined,
    51--Skull; bones topographically enumerated, 53--Bones of the
    limbs, 59--Synonymic list of bones, 59.


                              CHAPTER IV.

    MODIFICATIONS OF THE SKELETON                                    63

    Branchiostoma, 63--Cyclostomes, 64--Chondropterygians,
    66--Holocephali, 70--Ganoids, 71--Dipnoi, 71--Chondrostei,
    74--Polypteroidei, 77--Lepidosteoidei, 80--Amioidei,
    82--Teleostei, 83--Classification of the bones of the
    Teleosteous skull according to the vertebral doctrine,
    85--their morphological classification, 86--Limb-bones of
    Teleosteans, 92.


                              CHAPTER V.

    MYOLOGY                                                          93

    General arrangement of the Muscles, 93--Electric organs, 94.


                              CHAPTER VI.

    NEUROLOGY                                                        96

    Of Branchiostoma, 96--Spinal chord, 96--Brain, its size, 97--Brain
    of Osseous fishes, 97--of Ganoids, 98--of Chondropterygians,
    100--of Cyclostomes, 101--Spino-cerebral nerves, 103--Spinal
    nerves, 107--Sympathic system, 108.


                             CHAPTER VII.

    THE ORGANS OF SENSE                                             109

    Smell, 109--Sight, 111--Hearing; connection of the ear with the
    air-bladder, 116--Taste, 119--Touch, 120.


                             CHAPTER VIII.

    THE ORGANS OF NUTRITION AND DIGESTION                           121

    Food and mode of feeding, 121--Buccal and abdominal cavities and
    their openings, 123--Mouth and tongue, 123--Forms, texture,
    and arrangement of teeth, 124--Intestinal tract, 127--Liver,
    132--Pancreas, 133--Spleen, 133.


                              CHAPTER IX.

    ORGANS OF RESPIRATION                                           135

    Respiration, 135--Structure and arrangement of the gills,
    136--Pseudobranchiæ, 140--Accessory respiratory organs,
    142--Air-bladder; its varieties, structure, and functions, 142.


                              CHAPTER X.

    ORGANS OF CIRCULATION                                           150


                              CHAPTER XI.

    URINARY ORGANS                                                  155


                             CHAPTER XII.

    ORGANS OF REPRODUCTION                                          157

    Fishes are dioecious, 157--Hermaphroditism, 157--Oviparous and
    viviparous fishes, 157--Generative organs of Branchiostoma,
    157--of Cyclostomes; their ova, 158--Female organs of
    Teleosteans and their ova, 158--Instances of females taking
    care of their progeny, 160--Male organs of Teleosteans,
    162--Instances of males taking care of their progeny,
    163--Generative organs of Ganoids, 163--of Chondropterygians
    and their ova, 166.


                             CHAPTER XIII.

    GROWTH AND VARIATION OF FISHES                                  170

    Changes of form of the body or certain parts, normally accompanying
    growth, 170--Changes dependent on sexual development,
    176--Secondary sexual differences, 176--Mixogamous, polygamous,
    and monogamous fishes, 177--Hybridism as a cause
    of variation, 178--Regular and irregular growth of fishes,
    178--Leptocephali not a normal state of development, 179--Changes
    of colour of the muscles and external parts; chromatophors,
    182--Albinism, 183.


                             CHAPTER XIV.

    DOMESTICATED AND ACCLIMATISED FISHES, ETC.                      185

    Domesticated fishes, 185--Acclimatisation of fishes,
    185--Artificial impregnation of ova, 186--Tenacity of life,
    186--Reproduction of lost parts, 188--Hybernation, 188--Useful
    fishes, 189--Poisonous fishes, 189--Poison-organs, 190.


                              CHAPTER XV.

    DISTRIBUTION OF FISHES IN TIME                                  193

    Oldest fish-remains, 193--Devonian fishes, 194--Carboniferous,
    196--Permian, 197--Triassic, 197--Liassic, 198--Oolitic,
    199--Cretaceous, 199--Tertiary, 200--Post-pliocene, 201.


                             CHAPTER XVI.

    THE DISTRIBUTION OF EXISTING FISHES OVER THE EARTH’S
      SURFACE.--GENERAL REMARKS                                     202

    Freshwater-, Marine-, and Brackish-water Fishes, 202--Changes of
    the habitat of numerous fishes, active, 203--or dependent on
    geological changes, 204--Agencies operating upon the distribution
    of Freshwater and Marine fishes, 205.


                             CHAPTER XVII.

    THE DISTRIBUTION OF FRESHWATER FISHES                           208

    List of Freshwater Fishes, 208--Continuous and interrupted range
    of distribution, 209--The ways of dispersal of Freshwater
    fishes, 211--A wide range of a type is not necessarily proof of
    its antiquity, 212--Each fauna is composed of ancient, autochthont,
    and immigrant species, 213--Division of the globe
    into zoological regions; freshwater fishes have been spread in
    circumpolar zones, 215--Cyprinidæ and Siluridæ, most important
    families in recognising the zoo-geographical regions,
    216--Division of the faunæ of Freshwater fishes, 217--I.
    _Equatorial Zone_, 218--Indian Region, 220--African Region,
    227--Tropical American or Neotropical Region, 233--Tropical
    Pacific Region, 238--II. _Northern Zone_, 240--Europe-Asiatic
    or Palæarctic Region, 243--North American or Nearctic
    Region, 246--III. _Southern Zone_, with Tasmanian, New
    Zealand, and Fuegian Sub-regions, 248.


                            CHAPTER XVIII.

    THE FISHES OF THE BRACKISH WATER                                251


                             CHAPTER XIX.

    THE DISTRIBUTION OF MARINE FISHES                               255

    Shore-fishes, Pelagic, and Deep-sea fishes, 255--List of
    Shore-fishes, 257--Oceanic areæ as determined by Shore-fishes,
    259--Distribution of Shore-fishes compared with that of
    Freshwater-fishes, 260--I. _Arctic Ocean_, 261--II. _Northern
    Temperate Zone_, 262--Temperate North-Atlantic, 262--with
    British, 263--Mediterranean, 264--and North American districts,
    266--Temperate North-Pacific, 268--with Kamtschatkan,
    269--Japanese, 270--and Californian districts, 271--III.
    _Equatorial Zone_, 272--with Tropical Atlantic, 278--Indo-Pacific
    Ocean, 278--and the Pacific Coasts of Tropical America,
    279--IV. _Southern Temperate Zone_, 281--with the Cape of Good
    Hope, 283--South Australia and New Zealand, 283--Chile, 288--and
    Patagonia, 289--V. _Antarctic Ocean_, 289.


                              CHAPTER XX.

    DISTRIBUTION OF PELAGIC FISHES                                  292


                             CHAPTER XXI.

    THE FISHES OF THE DEEP SEA                                      296

    Deep-sea fishes a recent discovery, 296--Physical conditions affecting
    these fishes, 297--Characteristics of Deep-sea fishes, 299--Their
    vertical and horizontal distribution, 304--List of Deep-sea
    fishes, 305.


                   SYSTEMATIC AND DESCRIPTIVE PART.


                    FIRST SUB-CLASS--PALÆICHTHYES.

                                                                   PAGE
    FIRST ORDER--CHONDROPTERYGII                                    313

      I. _Plagiostomata_                                            313

        A. _Selachoidei--Sharks_                                    314

          Families: Carchariidæ (Blue Shark, Tope, Hammerhead,
          Hound), 316--Lamnidæ (Porbeagle, Carcharodon,
          Fox-Shark, Basking-Shark), 319--Rhinodontidæ,
          323--Notidanidæ, 324--Scylliidæ (Dog-fishes),
          325--Hybodontidæ, 328--Cestraciontidæ (Port Jackson
          Shark), 328--Spinacidæ (Spiny Dogs, Greenland
          Shark), 330--Rhinidæ, 334--Pristiophoridæ, 335.

        B. _Batoidei--Rays_                                         335

          Families: Pristidæ (Saw-fishes), 336--Rhinobatidæ,
          337--Torpedinidæ (Electric Rays), 338--Rajidæ (Rays
          and Skates), 340--Trygonidæ (Sting Rays), 342--Myliobatidæ
          (Eagle Rays), 344.

     II. _Holocephala_                                              348

          Family: Chimæridæ, 348.


    SECOND ORDER--GANOIDEI                                          350

        I. _Placodermi_                                             351

       II. _Acanthodini_                                            355

      III. _Dipnoi_                                                 355

          Families: Sirenidæ (Lepidosiren, Protopterus, Ceratodus),
          355--Ctenododipteridæ, 359--Phaneropleuridæ, 360.

       IV. _Chondrostei_                                            360

          Families: Acipenseridæ (Sturgeons), 360--Polyodontidæ,
          362.

        V. _Polypteroidei_                                          363

          Families: Polypteridæ, 364--Saurodipteridæ,
          365--Coelacanthidæ, 365--Holoptychidæ, 365.

       VI. _Pycnodontoidei_                                         366

          Families: Pleurolepidæ, 366--Pycnodontidæ, 366.

      VII. _Lepidosteoidei_                                         367

          Families: Lepidosteidæ, 367--Sauridæ, 368--Stylodontidæ,
          368--Sphærodontidæ, 368--Aspidorhynchidæ,
          369--Palæoniscidæ, 369--Platysomidæ, 370.

     VIII. _Amioidei_                                               370

           Families: Caturidæ, 371--Leptolepidæ, 371--Amiidæ
           (Bow-fin), 371.


                     SECOND SUB-CLASS--TELEOSTEI.

    FIRST ORDER--ACANTHOPTERYGII                                    374

        I. _A. perciformes_                                         374

          Families: Percidæ (Freshwater-Perches, Bass, Sea-Perches,
          Centrarchus), 375--Squamipinnes (Coral-Fishes),
          397--Mullidæ (Red-Mullets), 403--Sparidæ
          (Sea-breams), 405--Hoplognathidæ, 410--Cirrhitidæ,
          410--Scorpænidæ, 412--Nandidæ, 418--Polycentridæ,
          418--Teuthididæ, 418.

       II. _A. beryciformes_                                        419

          Family: Berycidæ, 420.

      III. _A. kurtiformes_                                         424

           Family: Kurtidæ, 424.

       IV. _A. polynemiformes_                                      425

           Family: Polynemidæ, 425.

        V. _A. sciæniformes_                                        426

           Family: Sciænidæ (Meagres), 426.

       VI. _A. xiphiiformes_                                        431

           Family: Xiphiidæ (Sword-fishes), 431.

      VII. _A. trichiuriformes_                                     433

           Families: Trichiuridæ (Scabbard-fishes, Hairtails),
           433--Palæorhynchidæ, 437.


     VIII. _A. cotto-scombriformes_                                 438

          Families: Acronuridæ (Surgeons), 438--Carangidæ
          (Horse-Mackerels, Pilot-fish, Boar-fish), 440--Cyttidæ
          (John Dorey), 450--Stromateidæ, 452--Coryphænidæ
          (Dolphin, Sun-fish), 452--Nomeidæ,
          455--Scombridæ (Mackerel, Tunny, Bonito, Albacore,
          Sucking-fish), 456--Trachinidæ (Stare-gazer,
          Weever, etc.), 462--Malacanthidæ, 467--Batrachidæ,
          467--Psychrolutidæ, 469--Pediculati (Angler,
          Antennarius, etc.), 469--Cottidæ (Bull-heads, Gurnards),
          476--Cataphracti (Flying Gurnards), 480--Pegasidæ,
          482.

       IX. _A. gobiiformes_                                         483

          Families: Discoboli (Lump-suckers), 483--Gobiidæ
          (Gobies, Dragonets), 485.

        X. _A. blenniiformes_                                       490

          Families: Cepolidæ (Band-fishes), 490--Trichonotidæ,
          490--Heterolepidotidæ, 491--Blenniidæ (Wolf-fish,
          Blennies), 492--Acanthoclinidæ, 498--Mastacembelidæ,
          499.

       XI. _A. mugiliformes_                                        499

          Families: Sphyrænidæ (Barracudas), 499--Atherinidæ
          (Atherines), 500--Mugilidæ (Mullets), 501.

      XII. _A. gastrosteiformes_                                    504

          Families: Gastrosteidæ (Sticklebacks), 504--Fistulariidæ
          (Flute-mouths), 507.

     XIII. _A. centrisciformes_                                     508

          Family: Centriscidæ, 508.

      XIV. _A. gobiesociformes_                                     510

          Family: Gobiesocidæ, 512.

       XV. _A. channiformes_                                        513

          Family: Ophiocephalidæ, 513.

      XVI. _A. labyrinthibranchii_                                  514

          Families: Labyrinthici (Climbing Perch, Gourami),
          514--Luciocephalidæ, 519.

     XVII. _A. lophotiformes_                                       519

          Family: Lophotidæ, 519.

    XVIII. _A. tæniiformes_                                         520

          Family: Trachypteridæ (Ribbon-fishes), 520.

      XIX. _A. notacanthiformes_                                    523

          Family: Notacanthidæ, 523.


    SECOND ORDER--ACANTHOPTERYGII PHARYNGOGNATHI                    523

          Families: Pomacentridæ (Coral-fishes), 524--Labridæ
          (Wrasses, Parrot-wrasses), 525--Embiotocidæ,
          533--Chromides, 534.

    THIRD ORDER--ANACANTHINI                                        537

        I. _A. gadoidei_                                            537

          Families: Lycodidæ, 537--Gadidæ (Cod-fishes, Hake,
          Burbot, Ling, Rockling, Torsk), 539--Ophidiidæ
          (Brotula, Fierasfer, Sand-eel, Congrogadus),
          546--Macruridæ, 551.

       II. _A. pleuronectoidei_                                     553

          Family: Pleuronectidæ (Flat-fishes), 553.


    FOURTH ORDER--PHYSOSTOMI                                        559

          Families: _Siluridæ_; their skeleton, 559--divided into
          eight subdivisions and sixteen groups; Clariina,
          563--Plotosina, 563--Silurina, 565--Hypophthalmina,
          566--Bagrina, 567--Amiurina, 567--Pimelodina,
          568--Ariina, 569--Doradina, 572--Rhinoglanina,
          573--Malapterurina (Electric Catfish), 574--Hypostomatina
          (Preñadillas, Loricaria, etc.), 575--Aspredinina,
          580--Nematogenyina and Trichomycterina, 581--Stegopholina,
          581.

          Families of Physostomi continued: Scopelidæ,
          582--_Cyprinidæ_ (Carps), 587--divided into fourteen
          groups, viz. Catostomina (Suckers), 588--Cyprinina (Carp,
          Crucian Carp, Gold-fish, Barbels, Gudgeons),
          589--Rohteichthyina, 596--Leptobarbina, 597--Rasborina,
          597--Semiplotina, 598--Xenocypridina, 598--Leuciscina
          (White fish, Tench, Dace, etc.), 598--Rhodeina,
          601--Danionina, 601--Hypophthalmichthyina,
          602--Abramidina (Bream, Bleak), 602--Homalopterina,
          604--Cobitidina (Loaches), 604.

          Families of Physostomi continued: Kneriidæ,
          606--Characinidæ, 606--Cyprinodontidæ, 613--Heteropygii
          (Blind Fish of the Mammoth Cave), 618--Umbridæ,
          619--Scombresocidæ (Gar-pike, Saury, Half-beak, Flying
          Fish), 619--Esocidæ (Pike), 623--Galaxiidæ, 624--Mormyridæ,
          625--Sternoptychidæ, 627--Stomiatidæ, 629.

          Families of Physostomi continued--_Salmonidæ_: Salmo,
          difficulty of distinguishing species, 630; constant
          specific characters, 635--hybrids, 638--sexual development,
          638--migratory species and their retention in freshwater,
          639--Growth of Salmonoids, 641--their domestication and
          acclimatisation, 641--species enumerated, 642--Smelt and
          Capelin, 646--Coregonus, 647--Grayling, 649--marine
          genera, 650.

          Families of Physostomi continued: Percopsidæ,
          651--Haplochitonidæ, 651--Gonorhynchidæ, 652--Hyodontidæ
          (Moon-eye), 653--Pantodontidæ, 653--Osteoglossidæ,
          653--Clupeidæ (Herrings, Anchovies, Shads, Mossbanker,
          Menhaden, etc.), 655--Bathythrissidæ, 663--Chirocentridæ,
          663--Alepocephalidæ, 664--Notopteridæ, 664--Halosauridæ,
          665--Hoplopleuridæ, 665--Gymnotidæ (Electric Eel),
          666--Symbranchidæ, 668--Murænidæ (Eels, Congers, Murænas,
          etc.), 669.


    FIFTH ORDER--LOPHOBRANCHII                                      678

        Families: Solenostomidæ, 678--Syngnathidæ (Pipe-fishes,
        Sea-horses), 679.


    SIXTH ORDER--PLECTOGNATHI                                       683

        Families: Sclerodermi (File-fishes, Coffer-fishes),
        684--Gymnodontes (Globe-fishes, Sun-fish), 686.


                    THIRD SUB-CLASS--CYCLOSTOMATA.

        Families: Petromyzontidæ (Lampreys), 691--Myxinidæ, 694.


                    FOURTH SUB-CLASS--LEPTOCARDII.

        Family: Cirrhostomi (Lancelets), 696.


                               APPENDIX.

    DIRECTIONS FOR COLLECTING AND PRESERVING FISHES                 697

    ALPHABETICAL INDEX                                              707




                         INTRODUCTORY REMARKS.


According to the views generally adopted at present, all those
Vertebrate animals are referred to the Class of Fishes, which living in
water, breathe air dissolved in water by means of gills or branchiæ;
whose heart consists of a single ventricle and single atrium; whose
limbs, if present, are modified into fins, supplemented by unpaired,
median fins; and whose skin is either naked, or covered with scales or
osseous plates or bucklers. With few exceptions fishes are oviparous.
However, there are not a few members of this Class which show a
modification of one or more of these characteristics, as we shall see
hereafter, and which, nevertheless, cannot be separated from it. The
distinction between the Class of Fishes and that of Batrachians is very
slight indeed.

The branch of Zoology which treats of the internal and external
structure of fishes, their mode of life, and their distribution in
space and time, is termed Ichthyology.[1]




                              CHAPTER I.

                        HISTORY AND LITERATURE.


[Sidenote: Aristotle.]

The commencement of the history of Ichthyology coincides with that of
Zoology generally. ARISTOTLE (384–322 B.C.) had a perfect knowledge
of the general structure of fishes, which he clearly discriminates
from the Aquatic animals with lungs and mammæ, _i.e._ Cetaceans, and
from the various groups of Aquatic Invertebrates. He says that “the
special characteristics of the true fishes consist in the branchiæ and
fins, the majority having four fins, but those of an elongate form,
as the eels, having two only. Some, as the _Muræna_, lack the fins
altogether. The Rays swim with their whole body, which is spread out.
The branchiæ are sometimes furnished with an opercle, sometimes without
one, as is the case in the cartilaginous fishes.... No fish has hairs
or feathers; most are covered with scales, but some have a rough or
smooth skin. The tongue is hard, often toothed; and sometimes so much
adherent that it seems to be wanting. The eyes have no lids; nor are
any ears or nostrils visible, for what takes the place of nostrils is a
blind cavity. Nevertheless they have the senses of tasting, smelling,
and hearing. All have blood. All scaly fishes are oviparous, but the
cartilaginous fishes (with the exception of the Sea-devil, which
Aristotle places along with them) are viviparous. All have a heart,
liver, and gall-bladder; but kidneys and urinary bladder are absent.
They vary much in the structure of their intestines: for whilst the
mullet has a fleshy stomach like a bird, others have no stomachic
dilatation. Pyloric coeca are close to the stomach, variable in number;
there are even some, like the majority of the cartilaginous fishes,
which have none whatever. Two bodies are situated along the spine,
which have the function of testicles, and open towards the vent, and
which are much enlarged in the spawning season. The scales become
harder with age. Not being provided with lungs, they have no voice, but
several can emit grunting sounds. They sleep like other animals. In
the majority the females exceed the males in size; and in the Rays and
Sharks the male is distinguished by an appendage on each side of the
vent.”

Aristotle’s information on the habits of fishes, their migrations, mode
and time of propagation, utility, is, as far as it has been tested,
surprisingly correct. Unfortunately, only too often we lack the means
of recognising the species of which he gives a description. His ideas
of specific distinction were as vague as those of the fishermen whose
nomenclature he adopted; it never occurred to him that such popular
names are subject to change, or may be entirely lost with time, and
the difficulty of deciphering his species is further increased by the
circumstance that popular names are often applied by him to the same
fish, or that different stages of growth are designated by distinct
names. The number of fishes known to Aristotle seems to have been about
115, all of which are inhabitants of the Ægean Sea.

That one man should have discovered so many truths, and formed so
sure a base for Zoology, is less surprising than the fact that for
about eighteen centuries a science which seemed to offer particular
attractions to men gifted with power of observation, was no farther
advanced. Yet this is the case. Aristotle’s disciples, as well as his
successors, remained satisfied to be his copiers or commentators,
and to collect fabulous stories or vague notions. With very few
exceptions (such as _Ausonius_, who wrote a small poem, in which
he describes from his own observations the fishes of the Mosel)
authors entirely abandoned original research. And it was not until
about the middle of the sixteenth century that Ichthyology made a new
step in advance by the appearance of _Belon_, _Rondelet_, and
_Salviani_, who almost simultaneously published their grand works,
by which the idea of species was established definitely and for all
times.

       *       *       *       *       *

[Sidenote: Belon.]

P. BELON travelled in the countries bordering on the eastern
part of the Mediterranean, in the years 1547–50; he collected rich
stores of positive knowledge, which he deposited in several works. The
one most important for the progress of Ichthyology is that entitled “De
aquatilibus libri duo” (Paris 1553; small 4to.) Belon knows about 110
fishes, of which he gives rude, but generally recognisable, figures. In
his descriptions he pays regard to the classical as well as vernacular
nomenclature, and states the outward characteristics, sometimes even
the number of fin-rays, frequently also the most conspicuous anatomical
peculiarities.

Although Belon but rarely gives definitions of the terms used by him,
it is generally not very difficult to ascertain the limits which
he intended to assign to each division of aquatic animals. He very
properly divides them into such as are provided with blood, and into
those without it: two divisions, called in modern language Vertebrate
and Invertebrate aquatic animals. The former are classified by him
according to sizes, the further subdivisions being based on the
structure of the skeleton, mode of propagation, number of limbs, form
of the body, and on the physical character of the localities inhabited
by fishes. This classification is as follows:--

     I. The larger fishes or Cetaceans.

      _A._ Viviparous Cetaceans with bony skeletons (= Cetacea).

      _B._ Viviparous Amphibians.

        1. “With four limbs: Seals, Hippopotamus, Beaver, Otter, and
             other aquatic Mammalia.

        2. With two limbs: Mermaids, etc.

      _C._ Oviparous Amphibians (= Reptiles and Frogs).

      _D._ Viviparous Cartilaginous fishes.

        1. Of an oblong form (= Sharks).

        2. Of a flat form (= Rays and Lophius).

      _E._ Oviparous Cartilaginous fishes (= Sturgeons and Silurus).

      _F._ Oviparous Cetaceans, with spines instead of bones (=
            large marine fishes, like the Thunny, Sword-fish,
            Sciænoids, Bass, Gadoids, Trachypterus).

    II. Spinous Oviparous fishes of a flat form (= Pleuronectidæ).

   III. Fishes of a high form, like Zeus.

    IV. Fishes of a snake like form (= Eels, Belone, Sphyræna).

     V. Small Oviparous, spinous, scaly, marine fishes.

      1. Pelagic kinds.

      2. Littoral kinds.

      3. Kinds inhabiting rocky localities.


    VI. Fluviatile and Lacustrine fishes.

       *       *       *       *       *

[Sidenote: Salviani.]

The work of the Roman ichthyologist, H. SALVIANI (1514–72),
is characteristic of the high social position which the author held
as the physician of three popes. Its title is “Aquatilium animalium
historia” (Rom. 1554–57, fol.) It treats exclusively of the fishes of
Italy. Ninety-two species are figured on seventy-six plates which, as
regards artistic execution, are masterpieces of that period, although
those specific characteristics which nowadays constitute the value
of a zoological drawing, were entirely overlooked by the author or
artist. No attempt is made at a natural classification, but the allied
forms generally are placed in close proximity. The descriptions are
quite equal to those given by Belon, entering much into the details of
the economy and usefulness of the several species, and were evidently
composed with the view of collecting in a readable form all that might
prove of interest to the class of society in which the author moved.
Salviani’s work is of a high standard, most remarkable for the age in
which he lived. It could not fail to convey valuable instruction, and
to render Ichthyology popular in the country to the fauna of which it
was devoted, but it would not have advanced Ichthyology as science
generally; and in this respect Salviani is not to be compared with
Rondelet or Belon.

       *       *       *       *       *

[Sidenote: Rondelet.]

G. RONDELET (1507–1557) had the great advantage over Belon in
having received a medical education at Paris, and more especially in
having gone through a complete course of instruction in anatomy as a
pupil of Guentherus of Andernach. This is conspicuous throughout his
works--“Libri de Piscibus marinis” (Lugd. 1554, fol.); and “Universæ
aquatilium historiæ pars altera” (Lugd. 1555, fol.) Nevertheless
they cannot be regarded as more than considerably enlarged editions
of Belon’s work. For although he worked independently of the latter,
and differs from him in numerous details, the system adopted by
him is characterised by the same absence of the true principles of
classification. Rondelet had a much more extensive knowledge of
details. His work is almost entirely limited to European, and chiefly
Mediterranean, forms, and comprises not less than 197 marine and 47
freshwater fishes. His descriptions are more complete and his figures
much more accurate than those of Belon; and the specific account is
preceded by introductory chapters in which he treats in a general
manner on the distinctions, the external and internal parts, and on
the economy of fishes. Like Belon, he had no conception of the various
categories of classification--for instance, confounding throughout his
work the terms “genus” and “species;” but he had intuitively a notion
of what his successors called a “species,” and his principal object was
to collect and give as much information as possible of such species.

For nearly a century the works of Belon and Rondelet remained the
standard works of Ichthyology; but this science did not remain
stationary during this period. The attention of naturalists was now
directed to the products of foreign countries, especially the Spanish
and Dutch possessions in the New World; and in Europe the establishment
of anatomical schools and academies led to the careful investigation
of the internal anatomy of the most remarkable European forms. Limited
as these efforts were as to their scope, being directed either only to
the fauna of some district, or to the dissection of a single species,
they were sufficiently numerous to enlarge the views of naturalists,
and to destroy that fatal dependency on preceding authorities which had
continued to keep in bonds the minds of even such men as Rondelet and
Belon.

[Sidenote: W. Piso. G. Margrav.]

The most noteworthy of those who were active in tropical countries
are W. PISO and G. MARGRAV. They accompanied as physicians the Dutch
Governor, Prince Moritz of Nassau, to Brazil (1637–44). Margrav
especially studied the fauna of the country, and although he died
before his return to Europe, his observations were published by his
colleague, and embodied in a work “Historia naturalis Braziliæ”
(Lugd. 1648, fol.), in which the fourth book treats of the fishes. He
describes about 100 species, all of which had been previously unknown,
in a manner far superior to that of his predecessors. The accompanying
figures are not good, but nearly always recognisable, and giving a
fair idea of the form of the fish. Margrav himself, with the aid of an
artist, had made a most valuable collection of coloured drawings of the
objects observed and described by him, but many years were allowed to
pass before it was scientifically utilised by Bloch and others.

[Sidenote: Anatomists, 1600–1700.]

Of the men who left records of their anatomical researches, we may
mention BORELLI (1608–79), who wrote a work “De motu animalium” (Rom.
1680, 4to), in which he explained the mechanism of swimming, and the
function of the air-bladder; M. MALPIGHI (1628–94), who examined the
optic nerve of the sword-fish; the celebrated J. SWAMMERDAM (1637–80),
who described the intestines of numerous fishes; and J. DUVERNEY
(1648–1730), who entered into detailed researches of the organs of
respiration.

       *       *       *       *       *

A new era in the history of Ichthyology commences with _Ray_,
_Willughby_, and _Artedi_, who were the first to recognise
the true principles by which the natural affinities of animals should
be determined. Their labours stand in so intimate a connection with
each other that they represent only one stride in the progress of this
science.

       *       *       *       *       *

[Sidenote: Ray and Willughby]

J. RAY (born 1628 in Essex, died 1705), was the friend and
guide of F. WILLUGHBY (1635–72). They had recognised that a
thorough reform of the treatment of the vegetable and animal kingdoms
had become necessary; that the only way of bringing order into the
existing chaos was that of arranging the various forms with regard to
their structure; that they must cease to be burdened with inapplicable
passages and quotations of the ancient writers, and to perpetuate
the erroneous or vague notions of their predecessors. They abandoned
speculation, and adhered to facts only. One of the first results, and
perhaps the most important, of their method was, that having recognised
the “species” as such, they defined this term, and fixed it as the
base, from which all sound zoological knowledge has to start.

Although they had divided their work thus that Ray attended to the
plants principally, and Willughby to the animals, the “Historia
piscium” (Oxford, 1686, fol.), which bears Willughby’s name on the
titlepage, and was edited by Ray, is clearly their joint production. A
great part of the observations contained in it were collected during
their common journeys in Great Britain and on the Continent, and it is
no exaggeration to say that at that time these two Englishmen knew the
fishes of the Continent, especially those of Germany, better than any
other Continental zoologist.

By the definition of fishes as animals with blood, breathing by gills,
provided with a single ventricle of the heart, covered with scales or
naked; the Cetaceans are excluded. Yet, at a later period Ray appears
to have been afraid of so great an innovation as the separation of
whales from fishes, and, therefore, he invented a definition of fish
which comprises both. The fishes proper are then arranged in the
first place according to the cartilaginous or osseous nature of the
skeleton; further subdivisions being formed with regard to the general
form of the body, the presence or absence of ventral fins, the soft or
spinous structure of the dorsal rays, the number of dorsal fins, etc.
Not less than 420 species are thus arranged and described, of which
about 180 were known to the authors from autopsy: a comparatively
small proportion, descriptions and figures still forming at that time
in a great measure a substitute for collections and museums. With the
increasing accumulation of forms the want of a fixed nomenclature is
now more and more felt.

       *       *       *       *       *

[Sidenote: P. Artedi.]

PETER ARTEDI would have been a great ichthyologist if Ray or
Willughby had never preceded him. But he was fully conscious of the
fact that both had prepared the way for him, and therefore he derived
all possible advantages from their works. Born in 1705 in Sweden, he
studied with Linnæus at Upsala; from an early period he devoted himself
entirely to the study of fishes, and was engaged in the arrangement and
description of the ichthyological collection of _Seba_, a wealthy
Dutchman who had formed the then perhaps richest museum, when he was
accidentally drowned in one of the canals of Amsterdam in the year
1734, at an age of twenty-nine years. His manuscripts were fortunately
rescued by an Englishman, Cliffort, and edited by his early friend
Linnæus.

The work is divided into the following parts:--

1. In the “Bibliotheca Ichthyologica” Artedi gives a very complete list
of all preceding authors who have written on fishes, with a critical
analysis of their works.

2. The “Philosophia Ichthyologica” is devoted to a description of
the external and internal parts of fishes; Artedi fixes a precise
terminology of all the various modifications of the organs,
distinguishes between those characters which determine a genus and such
as indicate a species or merely a variety; in fact he establishes the
method and principles which subsequently have guided every systematic
ichthyologist.

3. The “Genera Piscium” contains well-defined diagnoses of forty-five
genera, for which he fixes an unchangeable nomenclature.

4. In the “Species Piscium” descriptions of seventy-two species,
examined by himself, are given; descriptions which even now are models
of exactitude and method.

5. Finally, in the “Synonymia Piscium” references to all previous
authors are arranged for every species, very much in the same manner
which is adopted in the systematic works of the present day.

[Sidenote: Linnæus.]

Artedi has been justly called the Father of Ichthyology. So perfect was
his treatment of the subject, that even LINNÆUS could no more
improve it, only modify and add to it; and as far as Ichthyology is
concerned, Linnæus has scarcely done anything beyond applying binominal
terms to the species properly described and classified by Artedi.

Artedi had divided the fishes proper into four orders, viz.
_Malacopterygii_, _Acanthopterygii_, _Branchiostegi_, and
_Chondropterygii_, of which the third only, according to our present
knowledge, appears to be singularly heterogeneous, as it comprises
_Balistes_, _Ostracion_, _Cyclopterus_, and _Lophius_. Linnæus, besides
separating the Cetaceans entirely from the class of fishes (at least
since the 10th edition of the “Systema Naturæ”) abandoned Artedi’s
order of Branchiostegi, but substituted a scarcely more natural
combination by joining it with Artedi’s Chondropterygians, under the
name of “Amphibia nantes.”

His classification of the genera appears in the 12th edition of the
“Systema,” thus--


       AMPHIBIA NANTES.


   _Spiraculis compositis._

       Petromyzon.
       Raia.
       Squalus.
       Chimæra.


   _Spiraculis solitariis._

       Lophius.
       Acipenser.
       Cyclopterus.
       Balistes.
       Ostracion.
       Tetrodon.
       Diodon.
       Centriscus.
       Syngnathus.
       Pegasus.


   PISCES APODES.

       Muræna.
       Gymnotus.
       Trichiurus.
       Anarhichas.
       Ammodytes.
       Ophidium.
       Stromateus.
       Xiphias.


   PISCES JUGULARES.

       Callionymus.
       Uranoscopus.
       Trachinus.
       Gadus.
       Blennius.


   PISCES THORACICI.

       Cepola.
       Echeneis.
       Coryphæna.
       Gobius.
       Cottus.
       Scorpæna.
       Zeus.
       Pleuronectes.
       Chæetodon.
       Sparus.
       Labrus.
       Sciæna.
       Perca.
       Gasterosteus.
       Scomber.
       Mullus.
       Trigla.


   PISCES ABDOMINALES.

       Cobitis.
       Amia.
       Silurus.
       Teuthis.
       Loricaria.
       Salmo.
       Fistularia.
       Esox.
       Elops.
       Argentina.
       Atherina.
       Mugil.
       Mormyrus.
       Exocœtus.
       Polynemus.
       Clupea.
       Cyprinus.

[Sidenote: Gronow and Klein.]

Two contemporaries of _Linnæus_ attempted a systematic arrangement
of fishes; both had considerable opportunities for their study,
especially in possessing extensive collections; but neither exercised
any influence on the progress of Ichthyology. The one, L. T. GRONOW,
a German who resided in Holland, closely followed the arrangements
proposed by Artedi and Linnæus, and increased the number of genera and
species from the contents of his own museum. He published two works,
“Museum Ichthyologicum” (Lugd. 1754–6, fol.), and “Zoophylacium” (Lugd.
1763–81, fol.); a posthumous work, containing numerous excellent
descriptions of new forms was published by J. E. Gray in 1854 under the
title of “Systema Ichthyologicum.” To Gronow also is due the invention
of preparing flat skins of fishes in a dry state, and preserving them
in the manner of a herbarium. The specimens thus prepared by him belong
to the oldest which have been preserved down to our time.

Much less important are the ichthyological labours of J. T. KLEIN
(1685–1759). They are embodied in five parts (_Missus_) of a work
entitled “Historia naturalis piscium” (Sedæ, 1740–9, 4to.) He regarded
a system merely as the means of recognising the various forms of
animals, not as the expression of their natural affinities; and that
method seemed to him to be the most perfect by which an animal could
be most readily determined. He eschewed all reference to minute or
anatomical characters. Hence his system is a series of the most
unnatural combinations, and we cannot be surprised that Linnæus passed
in silence over Klein’s labours.

       *       *       *       *       *

[Sidenote: Pupils and Successors of Linnæus]

The works of Artedi and Linnæus excited fresh activity, more especially
in Scandinavia, Holland, Germany, and England, such as has not been
equalled in the history of biological science either before or
after. Whilst some of the pupils and followers of Linnæus devoted
themselves to an examination and study of the fauna of their native
countries, others proceeded on voyages of discovery to foreign and
distant countries. Of these latter the following may be specially
mentioned:--_O. Fabricius_ worked out the Fauna of Greenland, _Kalm_
collected in North America, _Hasselquist_ in Egypt and Palestine,
_Brünnich_ in the Mediterranean, _Osbeck_ in Java and China,
_Thurnberg_ in Japan; _Forskål_ examined and described the fishes of
the Red Sea; _Steller_, _Pallas_, _S. T. Gmelin_, and _Güldenstedt_
traversed nearly the whole of the Russian Empire in Europe and
Asia. Others attached themselves as naturalists to the celebrated
circumnavigators of the last century, like the two _Forsters_ (father
and son), and _Solander_, who accompanied Cook; _Commerson_, who
travelled with Bougainville; and _Sonnerat_. Numerous new and startling
forms were discovered by those men, and the foundation was laid of the
knowledge of the geographical distribution of animals.

Of those who studied the fishes of their native country the most
celebrated are _Pennant_ (Great Britain), _O. F. Müller_ (Denmark),
_Duhamel_ (France), _Meidinger_ (Austria), _Cornide_ (Spain), _Parra_
(Cuba).

The materials brought together by those and other zoologists were so
numerous that, not long after the death of Linnæus, the necessity was
felt of collecting them in a compendious form. Several compilators
undertook this task; they embodied the recent discoveries in new
editions of Artedi’s and Linné’s classical works, but not possessing
either a knowledge of the subject or any critical discernment, they
only succeeded in covering those noble monuments under a mass of
confused rubbish. For Ichthyology it was fortunate that two men at
least, Bloch and Lacépède, made it a subject of long and original
research.

       *       *       *       *       *

[Sidenote: M. E. Bloch.]

MARK ELIEZER BLOCH, born in the year 1723 at Anspach in Germany,
practised as a physician in Berlin; he had reached an age of fifty-six
years when he commenced to write on ichthyological subjects. To
commence at his age a work in which he intended not only to give full
descriptions of the species known to him from specimens or drawings,
but also to illustrate every species in a style truly magnificent for
his time, was an undertaking of the execution of which an ordinary man
would have despaired. Yet he accomplished not only this task, but even
more, as we shall see hereafter.

His work consists of two divisions:--

1. “Oeconomische Naturgeschichte der Fische Deutschlands” (Berl.
1782–4, 4to. Plates in fol.)

2. “Naturgeschichte der auslændischen Fische” (Berl. 1785–95, 4to.
Plates in fol.)

Bloch’s work is unique, and probably will for ever remain so. Although
Cuvier fifty years later undertook a similar general work on fishes,
the subject had then become too extensive to allow of an attempt of
giving illustrations of all the species, or illustrations of a similar
size and costliness.

The first division of the work, which is devoted to a description of
the fishes of Germany, is entirely original, and based upon Bloch’s
own observations. His descriptions as well as figures were made from
nature, and are, with but few exceptions, still serviceable; many
continue to be the best existing in literature.

Bloch was less fortunate and is much less reliable in his natural
history of foreign fishes. For many of the species he had to rely
on more or less incorrect drawings and descriptions of travellers;
frequently, also, he was deceived as to the origin of specimens which
he acquired by purchase. Hence his accounts contain numerous confusing
errors which it would have been difficult to correct, if not nearly the
whole of the materials on which his work is based had been preserved in
the collections at Berlin.

After the completion of his Ichthyology Bloch occupied himself with
systematic work. He prepared a general system of fishes, in which he
arranged not only those described in his great work, but also those
with which he had become acquainted afterwards from the descriptions of
others. The work was ably edited and published after Bloch’s death by a
philologist, _J. G. Schneider_, under the title “M. E. Blochii Systema
ichthyologiæ iconibus ex. illustratum” (Berl. 1801, 8vo.) The number of
species enumerated in it amounts to 1519. The system is based upon the
number of the fins, the various orders being termed _Hendecapterygii_,
_Decapterygii_, etc. We need not add that an artificial method like
this led to the most unnatural combinations or severances.

[Sidenote: Lacépède.]

Bloch’s Ichthyology remained for many years the standard work, and,
by the great number of excellent illustrations, proved a most useful
guide to the student. But as regards originality of thought, Bloch was
far surpassed by his contemporary, B. G. E. DE LACÉPÈDE, born at Agen,
in France, in 1756, a man of great and general erudition, who died as
Professor of the Museum of Natural History of Paris in 1826.

Lacépède had to contend with great difficulties in the preparation
of his “Histoire des Poissons” (Paris, 1798–1803, 4to, in 5 vols.),
which was written during the most disturbed period of the French
Revolution. A great part of it was composed whilst the author was
separated from collections and books, and had to rely on his notes and
manuscripts only. Even the works of Bloch and other contemporaneous
authors remained unknown, or at least inaccessible, to him for a long
time. Therefore we cannot be surprised that his work abounds in all
those errors to which a compiler is subject. The same species not only
appears under two and more distinct specific names, but it sometimes
happens that the author understands so little the source from which
he derives his information that the description is referred to one
genus and the accompanying figure to another. The names of genera are
unduly multiplied; and the figures with which the work is illustrated
are far inferior to those of Bloch. Thus the influence of Lacépède
on the progress of Ichthyology was infinitely less than that of his
fellow-labourer; and the labour caused to his successors by correcting
the numerous errors into which he has fallen, probably outweighs the
assistance which they derived from his work.

[Sidenote: Anatomists.]

The work of the principal cultivators of Ichthyology in the period
between Ray and Lacépède was chiefly systematic and descriptive, but
also the internal organisation of fishes received attention from more
than one great anatomist. _Haller_, _Camper_, and _Hunter_, examined
the nervous system and organs of sense; and more especially _Alexander
Monro_ (the son) published a classical work, “The Structure and
Physiology of Fishes explained and compared with those of Man and other
Animals” (Edinb. 1785, fol.) The electric organs of fishes (_Torpedo_
and _Gymnotus_) were examined by _Réaumur_, _Allamand_, _Bancroft_,
_Walsh_, and still more exactly by _J. Hunter_. The mystery of the
propagation of the Eel called forth a large number of essays, and even
the artificial propagation of Salmonidæ was known and practised by
_Gleditsch_ (1764).

[Sidenote: Faunists.]

Bloch and Lacépède’s works were almost immediately succeeded by the
labours of _Cuvier_, but his early publications were of necessity
tentative, preliminary, and fragmentary, so that a short period elapsed
before the spirit infused by this great anatomist into Ichthyology
could exercise its influence on all workers in this field. Several
of such antecuvierian works must be mentioned on account of their
importance to our knowledge of certain Faunas: the “Descriptions and
Figures of Two Hundred Fishes collected at Vizagapatam on the coast
of Coromandel” (Lond. 1803; 2 vols. in fol.), by _Patrick Russel_;
and “An Account of the Fishes found in the River Ganges and its
branches” (Edinb. 1822; 2 vols. in 4to), by _F. Hamilton_ (formerly
_Buchanan_)--works distinguished by a greater accuracy of their
drawings (especially in the latter), than was ever attained before.
A “Natural History of British Fishes” was published by _E. Donovan_
(Lond. 8vo, 1802–8); and the Mediterranean Fauna formed the study of
the lifetime of _A. Risso_ (“Ichthyologie de Nice.” Paris, 1810, 8vo;
and “Histoire naturelle de l’Europe Meridionale.” Paris, 1827, 8vo). A
slight beginning in the description of the fishes of the United States
was made by _S. L. Mitchell_, who published, besides various papers, a
“Memoir on the Ichthyology of New York,” in 1815.[2]

       *       *       *       *       *

[Sidenote: G. Cuvier.]

G. CUVIER did not occupy himself with the study of fishes merely
because this class formed part of the “Règne animal,” but he devoted
himself to it with particular predilection. The investigation of their
anatomy, and especially of their skeleton, was taken up by him at an
early period, and continued until he had succeeded in completing so
perfect a framework of the system of the whole class that his immediate
successors could content themselves with filling up those details for
which their master had no leisure. Indefatigable in examining all the
external and internal characters of the fishes of a rich collection, he
ascertained the natural affinities of the infinite variety of fishes,
and accurately defined the divisions, orders, families, and genera
of the class, as they appear in the various editions of the “Règne
animal.” His industry equalled his genius: he opened connections with
almost every accessible part of the globe; not only French travellers
and naturalists, but also Germans, Englishmen, Americans, rivalled one
another to assist him with collections; and for many years the Muséum
of the Jardin des Plantes was the centre where all ichthyological
treasures were deposited. Thus Cuvier brought together a collection
the like of which had never been seen before, and which, as it contains
all the materials on which his labours were based, must still be
considered to be the most important. Soon after the year 1820, Cuvier,
assisted by one of his pupils, A. VALENCIENNES, commenced his great
work on fishes, “Histoire naturelles des Poissons,” of which the first
volume appeared in 1828. The earlier volumes, in which Cuvier himself
took his share, bear evidence of the freshness and love with which both
authors devoted themselves to their task. After Cuvier’s death in 1832
the work was left entirely in the hands of Valenciennes, whose energy
and interest gradually slackened, to rise to the old standard in some
parts only, as, for instance, in the treatise on the Herring. He left
the work unfinished with the twenty-second volume (1848), which treats
of the Salmonoids. Yet, incomplete as it is, it is indispensable to the
student.

There exist several editions of the work, which, however, have the same
text. One, printed in 8vo, with coloured or plain figures, is the one
in common use among ichthyologists. A more luxurious edition in 4to has
a different pagination, and therefore is most inconvenient to use.

As mentioned above, the various parts of the work are very unequally
worked out. Many of the species are described in so masterly a
manner that a greater excellency of method can hardly be conceived.
The history of the literature of these species is entered into with
minuteness and critical discernment; but in the later volumes, numerous
species are introduced into the system without any description, or
with a few words only, comparing a species with one or more of its
congeners. Cuvier himself, at a late period of his life, seems to have
grown indifferent as to the exact definition of his species: a failing
commonly observed among Zoologists when attention to descriptive
details becomes to them a tedious task. What is more surprising is,
that a man of his anatomical and physiological knowledge should have
overlooked the fact that secondary sexual characters are developed in
fishes as in any other class of animals, and that fishes undergo great
changes during growth; and, consequently, that he described almost
all such sexual forms and different stages of growth under distinct
specific and even generic names.

The system finally adopted by Cuvier is the following:--


                         _A._ POISSONS OSSEUX.

                I.--A BRANCHIES EN PEIGNES OU EN LAMES.

                    1. A MÂCHOIRE SUPÉRIEURE LIBRE.

                        a. _Acanthoptérygiens._

    Percoïdes.
    Polynèmes.
    Mulles.
    Joues cuirassées.
    Scienoïdes.
    Sparoïdes.
    Chétodonoïdes.
    Scomberoïdes.
    Muges.
    Branchies labyrinthiques.
    Lophioïdes.
    Gobioïdes.
    Labroïdes.


                        b. _Malacoptérygiens._

    _Abdominaux._
    Cyprinoïdes.
    Siluroïdes.
    Salmonoïdes.
    Clupeoïdes.
    Lucioïdes.

    _Subbrachiens._
    Sparoïdes.
    Pleuronectes.
    Discoboles.

    _Apodes._
    Murenoïdes.

                    2. A MÂCHOIRE SUPÉRIEURE FIXÉE.

    Sclérodermes.
    Gymnodontes.

                 II. A BRANCHIES EN FORME DE HOUPPES.

    Lophobranches.

               _B._ CARTILAGINEUX OU CHONDROPTÉRYGIENS.

    Sturioniens.
    Plagiostomes.
    Cyclostomes.

We have to compare this system with that of Linnæus if we wish
to measure the gigantic stride Ichthyology has made during the
intervening period of seventy years. The various characters employed
for classification have been examined throughout the whole class,
and their relative importance has been duly weighed and understood.
Though Linnæus had formed a category of “Amphibia nantes” for fishes
with a cartilaginous skeleton, which should coincide with Cuvier’s
“Poissons Cartilagineux,” he had failed to understand the very nature
of cartilage, apparently comprising by this term any skeletal framework
of less firmity than ordinary bone. Hence he considered _Lophius_,
_Cyclopterus_, _Syngnathus_ to be cartilaginous fishes. Adopting the
position and development of the ventral fins as a highly important
character, he was obliged to associate fishes with rudimentary and
inconspicuous ventral fins, like _Trichiurus_, _Xiphias_, etc., with
the true Eels. The important category of a “family” appears now in
Cuvier’s system fully established as that intermediate between genus
and order. Important changes in Cuvier’s system have been made and
proposed by his successors, but in the main it is still that of the
present day.

Cuvier had extended his researches beyond the living forms, into
the field of palæontology; he was the first to observe the close
resemblance of the scales of the fossil _Palæoniscus_ to those of the
living _Polypterus_ and _Lepidosteus_, the prolongation and identity of
structure of the upper caudal lobe in _Palæoniscus_ and the Sturgeons,
the presence of peculiar “fulcra” on the anterior margin of the dorsal
fin in _Palæoniscus_ and _Lepidosteus_: inferring from these facts
that that fossil genus was allied _either_ to the Sturgeons _or_ to
_Lepidosteus_. But it did not occur to him that there was a close
relationship between those recent fishes. _Lepidosteus_ and, with
it, the fossil genus remained in his system a member of the order of
_Malacopterygii abdominales_.

It was left to L. AGASSIZ (born 1807, died 1873) to point out the
importance of the character of the structure of the scales, and to open
a path towards the knowledge of a whole new sub-class of fishes, the
_Ganoidei_.

Impressed with the fact that the peculiar scales of _Polypterus_ and
_Lepidosteus_ are common to all fossil osseous fishes down to the
chalk, he takes the structure of the scales generally as the base for
an ichthyological system, and distinguishes four orders:--

1. _Placoids._--Without scales proper, but with scales of enamel,
sometimes large, sometimes small and reduced to mere points (Rays,
Sharks, and Cyclostomi, with the fossil _Hybodontes_).

2. _Ganoids._--With angular bony scales, covered with a thick
stratum of enamel: to this order belong the fossil Lepidoides,
Sauroides, Pycnodontes, and Coelacanthi; the recent Polypterus,
Lepidosteus, Sclerodermi, Gymnodontes, Lophobranches, and Siluroides;
also the Sturgeons.

3. _Ctenoids._--With rough scales, which have their free margins
denticulated: Chætodontidæ, Pleuronectidæ, Percidæ, Polyacanthi,
Sciænidæ, Sparidæ, Scorpænidæ, Aulostomi.

4. _Cycloids._--With smooth scales, the hind margin of which lacks
denticulation: Labridæ, Mugilidæ, Scombridæ, Gadoidei, Gobiidæ,
Murænidæ, Lucioidei, Salmonidæ, Clupeidæ, Cyprinidæ.

We have no hesitation in affirming that if Agassiz had had an
opportunity of acquiring a more extensive and intimate knowledge of
existing fishes before his energies were absorbed in the study of
their fossil remains, he himself would have recognised the artificial
character of his classification. The distinctions between cycloid and
ctenoid scales, between placoid and ganoid fishes are vague, and can
hardly be maintained. As far as the living and post-cretacean forms
are concerned, the vantage-ground gained by Cuvier was abandoned
by him; and therefore his system could never supersede that of his
predecessors, and finally shared the fate of every classification based
on the modifications of one organ only. But Agassiz has the merit of
having opened an immense new field of research by his study of the
infinite variety of fossil forms. In his principal work, “Recherches
sur les Poissons fossiles,” (Neuchatel, 1833–43, 4to, atlas in fol.),
he placed them before the world arranged in a methodical manner, with
excellent descriptions and illustrations. His power of discernment and
penetration in determining even the most fragmentary remains is truly
astonishing; and if his order of Ganoids is an assemblage of forms very
different from that as it is circumscribed now, he was at any rate the
first who recognised that such an order of fishes exists.

       *       *       *       *       *

[Sidenote: J. Müller.]

The discoverer of the _Ganoidei_ was succeeded by their explorer,
JOHANNES MÜLLER (born 1801, died 1858). In his classical memoir “Ueber
den Bau und die Grenzen der Ganoiden” (Berlin, 1846; 4to), he showed
that the Ganoids differed from all the other osseous fishes, and agreed
with the Plagiostomes, in the structure of their heart. By this primary
character, all heterogeneous elements, as _Siluroids_, _Osteoglossidæ_,
etc., were eliminated from the order as understood by Agassiz. On the
other hand, he did not recognise the affinity of _Lepidosiren_ to the
Ganoids, but established for it a distinct sub-class, _Dipnoi_, which
he placed at the opposite end of the system. By his researches into the
anatomy of the Lampreys and Amphioxus, their typical distinctness from
other cartilaginous fishes was proved; they became the types of two
other sub-classes, _Cyclostomi_ and _Leptocardii_.

Müller proposed several other not unimportant modifications of the
Cuvierian system; and although all cannot be maintained as the most
natural arrangements, yet his researches have given us a much more
complete knowledge of the organisation of the Teleosteous fishes,
and later enquiries have shown that, on the whole, the combinations
proposed by him require only some further modification and another
definition to render them perfectly natural.

Under the name of _Pharyngognathi_ he combined fishes with the lower
pharyngeals coalesced into one bone, viz. the Labroids, Chromides, and
Scombresoces. The association of the third family with the two former
seemed to himself a somewhat arbitrary proceeding; and it had to be
abandoned again, when a number of fishes which cannot be separated
from the Acanthopterygians, were found to possess the same united
pharyngeals.

A more natural combination is the union of the Cod-fishes with the
Flat-fishes into the order _Anacanthini_. Flat-fishes are in fact
nothing but asymmetrical Cod-fishes. Müller separates them from the
remaining Malacopterygians by the absence of a connecting duct between
the air-bladder and oesophagus. However, it must be admitted that the
examination of those fishes, and especially of the young stages, is not
complete enough to raise the question beyond every doubt, whether the
presence or absence of that duct is an absolutely distinctive character
between Anacanths and Malacopterygians.

Many of the families established by Cuvier were reexamined and better
defined by Müller, as may be seen from the following outline of his
system:--


                        Sub-classis I.--Dipnoi.

                         Ordo I.--Sirenoidei.

    Fam. 1. Sirenoidei.


                      Sub-classis II.--Teleostei.

                        Ordo I.--Acanthopteri.

    Fam. 1. Percoidei.
     „   2. Cataphracti.
     „   3. Sparoidei.
     „   4. Sciænoidei.
     „   5. Labyrinthiformes.
     „   6. Mugiloidei.
     „   7. Notacanthini.
     „   8. Scomberoidei.
     „   9. Squamipennes.
     „  10. Taenioidei.
     „  11. Gobioidei.
     „  12. Blennioidei.
     „  13. Pediculati.
     „  14. Theutyes.
     „  15. Fistulares.


                        Ordo II.--Anacanthini.

                 Sub-ordo I.--Anacanthini sub-brachii.

    Fam. 1. Gadoidei.
     „   2. Pleuronectides.


                   Sub-ordo II.--Anacanthini apodes.

    Fam. 1. Ophidini.


                      Ordo III.--Pharyngognathi.

             Sub-ordo I.--Pharyngognathi acanthopterygii.

    Fam. 1. Labroidei cycloidei.
     „   2. Labroidei ctenoidei.
     „   3. Chromides.


             Sub-ordo II.--Pharyngognathi malacopterygii.

    Fam. 1. Scomberesoces.


                         Ordo IV.--Physostomi.

                 Sub-ordo I.--Physostomi abdominales.

    Fam. 1. Siluroidei.
     „  2. Cyprinoidei.
     „   3. Characini.
     „   4. Cyprinodontes.
     „   5. Mormyri.
     „   6. Esoces.
     „   7. Galaxiæ.
     „   8. Salmones.
     „   9. Scopelini.
     „  10. Clupeidæ.
     „  11. Heteropygii.


            Sub-ordo II.--Physostomi apodes s. anguillares.

    Fam. 12. Murænoidei.
     „   13. Gymnotini.
     „   14. Symbranchii.


                        Ordo V.--Plectognathi.

    Fam. 1. Balistini.
     „   2. Ostraciones.
     „   3. Gymnodontes.


                       Ordo VI.--Lophobranchii.

    Fam. 1. Lophobranchi.


                      Sub-classis III.--Ganoidei.

                          Ordo I.--Holostei.

    Fam. 1. Lepidosteini.
     „   2. Polypterini.


                        Ordo II.--Chondrostei.

    Fam. 1. Acipenserini,
     „   2. Spatulariæ.


              Sub-classis IV.--Elasmobranchi s. Selachii.

                         Ordo I.--Plagiostomi.

                        Sub-ordo I.--Squalidæ.

    Fam. 1. Scyllia.
     „   2. Nyctitantes.
     „   3. Lamnoidei.
     „   4. Alopeciæ.
     „   5. Cestraciones.
     „   6. Rhinodontes.
     „   7. Notidani.
     „   8. Spinaces.
     „   9. Scymnoidei.
     „  10. Squatinæ.


                         Sub-ordo II.--Rajidæ.

    Fam. 11. Squatinorajæ.
     „   12. Torpedines.
     „   13. Rajæ.
     „   14. Trygones.
     „   15. Myliobatides.
     „   16. Cephalopteræ.


                        Ordo II.--Holocephali.

    Fam. 1. Chimaeræ.


            Sub-classis V.--Marsipobranchii s. Cyclostomi.

                         Ordo I.--Hyperoartii.

    Fam. 1. Petromyzonini.


                        Ordo II.--Hyperotreti.

    Fam. 1. Myxinoidei.


                     Sub-classis VI.--Leptocardii.

                         Ordo I.--Amphioxini.

    Fam. 1. Amphioxini.

[Sidenote: Discovery of Ceratodus.]

The discovery (in the year 1871) of a living representative of a
genus hitherto believed to be long extinct, _Ceratodus_, threw
a new light on the affinities of Fishes. The author who had the good
fortune of examining this fish, was enabled to show that, on the one
hand, it was a form most closely allied to _Lepidosiren_; on the
other, that it could not be separated from the Ganoid fishes, and
therefore that also _Lepidosiren_ was a Ganoid: a relation pointed
at already by Huxley in a previous paper on “Devonian Fishes.” This
discovery led to further considerations[3] of the relative characters
of Müller’s sub-classes, and to the system which is followed in the
present work.

Having followed the development of the ichthyological system down to
the latest time, we have to retrace our steps to enumerate the most
important contributions to Ichthyology which appeared contemporaneously
with or subsequently to the publication of Cuvier and Valenciennes’s
great work. As in other branches of Zoology, activity increased almost
with every year; and for convenience’s sake we may arrange these works
in three rubrics.


[Sidenote: Recent Works.]

        I.--VOYAGES, CONTAINING GENERAL ACCOUNTS OF ZOOLOGICAL
                             COLLECTIONS.


                             A. _French._

1. “Voyage autour du monde sur les Corvettes de S. M. l’Uranie et la
Physicienne, sous le commandement de M. Freycinet. Zoologie: Poissons
par _Quoy_ et _Gaimard_.” (Paris, 1824, 4to, atlas fol.)

2. “Voyage de la Coquille. Zoologie par _Lesson_.” (Paris,
1826–30, 4to, atlas fol.)

3. “Voyage de l’Astrolabe, sous le commandement de M. J. Dumont
d’Urville. Poissons par _Quoy_ et _Gaimard_.” (Paris, 1834,
8vo, atlas fol.)

4. “Voyage au Pôle Sud par M. J. Dumont d’Urville. Poissons par
_Hombron_ et _Jacquinot_.” (Paris, 1853–4, 8vo, atlas fol.)


                             B. _English._

1. “Voyage of H.M.S. Sulphur. Fishes by _J. Richardson_.” (Lond.
1844–5, 4to.)

2. “Voyage of H.M.S.S. Erebus and Terror. Fishes by _J. Richardson_.”
(Lond. 1846. 4to.)

3. “Voyage of H.M.S. Beagle. Fishes by _L. Jenyns_.” (Lond. 1842,
4to.)

4. “Voyage of H.M.S. Challenger. Fishes by _A. Günther_.” (in
course of publication).


                             C. _German._

1. “Reise der österreichischen Fregatte Novara. Fische von _R.
Kner_.” (Wien. 1865, 4to.)


                             II.--FAUNAE.

                          A. _Great Britain._

1. _R. Parnell_, “The Natural History of the Fishes of the Firth
of Forth.” (Edinb. 1838, 8vo.)

2. _W. Yarrell_, “A History of British Fishes.” (3d edit. Lond.
1859, 8vo.)

3. _J. Couch_, “A History of the Fishes of the British Islands.”
(Lond. 1862–5, 8vo.)


                     B. _Denmark and Scandinavia._

1. _H. Kröyer_, “Danmark’s Fiske.” (Kjöbnh. 1838–53, 8vo.)

2. _S. Nilsson_, “Skandinavisk Fauna.” (Vol. IV. Fiskarna. Lund.
1855, 8vo.)

3. _Fries och Ekström_, “Skandinavians Fiskar.” (Stockh. 1836,
4to, with excellent plates.)


                             C. _Russia._

1. _Nordmann_, “Ichthyologie Pontique,” in “Voyage dans la Russie
méridionale de _Demidoff_.” (Tom. iii. Paris, 1840, 8vo, atlas
fol.)


                             D. _Germany._

1. _Heckel_ and _Kner_, “Die Süsswasser-fische der
Oesterreichischen Monarchie.” (Leipz. 1858, 8vo.)

2. _C. T. E. Siebold_, “Die Süsswasser-fische von Mitteleuropa.”
(Leipz. 1863, 8vo.)


                     E. _Italy and Mediterranean._

1. _Bonaparte_, “Iconografia della Fauna Italica.” Tom. iii.
Pesci. (Roma, 1832–41, fol.) (Incomplete.)

2. _Costa_, “Fauna del Regno di Napoli.” Pesci. (Napoli, 4to,
about 1850.) (Incomplete.)


                             F. _France._

1. _E. Blanchard_, “Les Poissons des eaux douces de la France.”
(Paris, 1866, 8vo.)


                       G. _Pyrenean Peninsula._

The freshwater Fish-fauna of Spain and Portugal was almost unknown,
until _F. Steindachner_ paid some visits to those countries for
the purpose of exploring the principal rivers. His discoveries are
described in several papers in the “Sitzungsberichte der Akademie
zu Wien.” _B. du Bocage_ and _F. Capello_ contributed towards the
knowledge of the marine fishes on the coast of Portugal. (“Jorn.
Scienc. Acad. Lisb.”)


                          H. _North America._

1. _J. Richardson_, “Fauna Boreali Americana.” Part III. Fishes.
(Lond. 1836, 4to.) The species described in this work are nearly all
from the British possessions in the North.

2. _Dekay_, “Zoology of New York.” Part IV. Fishes. (New York,
1842, 4to.)

3. “Reports of the United States Commission of Fish and Fisheries.”
(5 vols. Washingt. 1873–79, 8vo. In progress. Contains most valuable
information.)

Besides these works, numerous descriptions of North American freshwater
fishes have been published in the Reports of the various U. S.
Government expeditions, and in North American scientific journals, by
_Storer_, _Baird_, _Girard_, _W. O. Ayres_, _Cope_, _Jordan_, _Brown
Goode_, etc.; but a good general, and especially critical, account of
the fishes of the United States is still a desideratum.


                             I.--_Japan._

1. “Fauna Japonica.” Poissons par _H. Schlegel_. (Lugd. Bat. 1850,
fol.)


J.--_East Indies; Tropical parts of the Indian and Pacific Oceans._

1. _E. Rüppell_, “Atlas zu der Reise im Nördlichen Afrika.”
(Frankf. 1828, fol.)

2. _E. Rüppell_, “Neue Wirbelthiere. Fische.” (Frankf. 1837, fol.)

These two works form the standard works for the student of the Fishes
of the Red Sea, and are distinguished by a rare conscientiousness and
faithfulness of the descriptions and figures; so that there is no
other part of the tropical seas, with the fishes of which we are so
intimately acquainted, as with those of the Red Sea. But these works
have a still wider range of usefulness, in as much as only a small
proportion of the fishes is limited to that area, the majority being
distributed over the Indian Ocean into Polynesia. Rüppel’s works were
supplemented by the two first of the following works:--

3. _R. L. Playfair_ and _A. Günther_, “The Fishes of Zanzibar.” (Lond.
1866, 4to); and

4. _C. B. Klunzinger_, “Synopsis der Fische des Rothen Meers.”
(Wien. 1870–1, 8vo.)

5. _T. Cantor_, “Catalogue of Malayan Fishes.” (Calcutta, 1850,
8vo.)

6. _F. Day_, “The Fishes of India.” (Lond. 1875, 4to, in
progress); contains an account of the freshwater and marine species,
and is not yet complete.

7. _A. Günther_, “Die Fische der Südsee.” (Hamburg, 4to; from
1873, in progress.)

Unsurpassed in activity, as regards the exploration of the fish fauna
of the East Indian Archipelago, is _P. Bleeker_, a surgeon in the
service of the Dutch East Indian Government (born 1819, died 1878),
who, from the year 1840, for nearly thirty years, amassed immense
collections of the fishes of the various islands, and described them
in extremely numerous papers, published chiefly in the Journals of the
Batavian Society. When his descriptions and the arrangement of his
materials evoked some criticism, it must be remembered that, at the
time when he commenced his labours, and for many years afterwards,
he stood alone, without the aid of a previously named collection on
which to base his first researches, and without other works but that
of Cuvier and Valenciennes. He had to create for himself a method of
distinguishing species and of describing them; and afterwards it would
have been difficult for him to abandon his original method and the
principles by which he had been guided for so many years. His desire
of giving a new name to every individual, to every small assemblage
of species wherever practicable, or of changing an old name, detracts
not a little from the satisfaction with which his works would be
used otherwise. It is also surprising that a man with his anatomical
knowledge and unusual facilities should have been satisfied with the
merely external examination of the specimens. But none of his numerous
articles contain anything relating to the anatomy, physiology, or
habits of the fishes which came under his notice; hence his attempts
at systematic arrangement are very far from indicating an advance in
Ichthyology.

Soon after his return to Europe (1860) Bleeker commenced to collect the
final results of his labours in a grand work, illustrated by coloured
plates, “Atlas Ichthyologique des Indes Orientales Néerlandaises.”
(Amsterd. fol. 1862); the publication of which was interrupted by the
author’s death in 1878.


                             K.--_Africa._

1. _A. Günther_, “The Fishes of the Nile” in Petherick’s “Travels
in Central Africa.” (Lond. 1869, 8vo.)

2. _W. Peters_, “Naturwissenschaftliche Reise nach Mossambique.
IV. Flussfische.” (Berl. 1868, 4to.)


                 L.--_West Indies and South America._

1. _L. Agassiz_, “Selecta genera et species Piscium, quæ in
itinere per Brasiliam, collegit J. B. de Spix.” (Monach. 1829, fol.)

2. _F. de Castlenau_, “Animaux nouveaux ou rares, recueillis
pendant l’expedition dans les parties centrales de l’Amérique du Sud.
Poissons.” (Paris, 1855, 4to.)

3. _A. Günther_, “An account of the Fishes of the States of
Central America.” (In Trans. Zool. Soc. 1868.)

4. _L. Vaillant_ and _F. Bocourt_, “Mission scientifique au
Mexique et dans l’Amérique centrale. Poissons.” (Paris, 1874, 4to.) (In
progress.)

_F. Poey_, the celebrated naturalist of Havannah, devoted many
years of study to the Fishes of Cuba, His papers and memoirs are
published partly in two periodicals, issued by himself, under the
title of “Memorias sobre la Historia natural de la Isle de Cuba” (from
1851), and “Repertorio Fisico-natural de la Isla de Cuba” (from 1865),
partly in North American scientific journals. And, finally, _F.
Steindachner_ has published many contributions, accompanied by
excellent figures, to our knowledge of the Fishes of Central and South
America.


                          M.--_New Zealand._

1. _F. W. Hutton_ and _J. Hector_, “Fishes of New Zealand.”
(Wellingt. 1872, 8vo.)


                         N.--_Arctic Regions._

1. _G. Lütken_, “A revised Catalogue of the Fishes of Greenland,”
in “Manual of the Natural History, Geology, and Physics of Greenland.”
(Lond. 1875, 8vo.) Although only a nominal list, this catalogue is
useful, as it contains references to all the principal works in which
Arctic fishes have been described. The fishes of Spitzbergen were
examined by _A. J. Malmgren_ (1865).


                        III.--ANATOMICAL WORKS.

The number of authors who worked on the anatomy of fishes is almost
as great as that of faunists; and we should go beyond the limits of
the present work if we mentioned more than the most prominent and
successful. _M. H. Rathke_, _J. Müller_, _J. Hyrtl_, and _H. Stannius_
left scarcely any organ unexamined, and their researches had a direct
bearing either on the relation of the class of fishes to the other
vertebrates, or on the systematic arrangement of the fishes themselves.
_E. E. von Baer_, _F. de Filippi_, _C. Vogt_, _W. His_, _W. K. Parker_,
and _F. M. Balfour_ worked at their embryology; _A. Kölliker_ and
_G. Pouchet_ at their histology. The osteology was specially treated
by _G. Bakker_, _F. C. Rosenthal_, _L. Agassiz_, and _C. Gegenbaur_;
the nervous system by _Gottsche_, _Philipeaux_, _Stannius_, _L.
de Sanctis_, _L. Stieda_, _Baudelot_ and _Miclucho-Maclay_; the
organ of hearing by _E. H. Weber_, _C. Hasse_, and _G. Retzius_.
The electric fishes were examined by _E. Geoffroy_, _C. Matteuci_,
_P. Pacini_, _T. Bilharz_, and _Max Schultze_. The development and
metamorphosis of the Lamperns was made the subject of research by _H.
Müller_, _M. Schultze_, and _P. Owsjannikow_; Müller’s examination of
_Branchiostoma_ was continued by _J. Marcusen_, _A. Kovalevsky_, _L.
Stieda_, _W. Müller_, _C. Hasse_, _T. Huxley_, and _F. M. Balfour_. The
most comprehensive accounts of the anatomy of fishes are contained in
the following works:--

1. _H. Stannius_, “Zootomic der Fische,” 2d edit. (Berl. 1854,
8vo.)

2. _R. Owen_, “Anatomy of Vertebrates,” vol. i. (Lond. 1866, 8vo.)

3. _R. Owen_, “Lectures on the Comparative Anatomy and Physiology
of the Vertebrate Animals.” Part I. Fishes. (Lond. 1846, 8vo.)

4. _T. Huxley_, “A Manual of the Anatomy of Vertebrated Animals.”
(Lond. 1871, 16mo.)

       *       *       *       *       *

[Sidenote: Latest Systematic Works.]

It has been mentioned above that the great work of Cuvier and
Valenciennes had been left incomplete. Several authors, therefore,
supplied detailed accounts of the orders omitted in that work. _Müller_
and _Henle_ published an account of the Plagiostomes, and _Kaup_ of
the Murænidæ and Lophobranchii. _A. Duméril_, finally, commenced an
“Histoire naturelle des Poissons ou Ichthyologie générale,” of which,
however, two volumes only appeared, containing a complete account
of the “Plagiostomes” (Paris, 1865, 8vo.), and of the “Ganoids and
Lophobranchs.” (Paris, 1870, 8vo.)

So great an activity had prevailed in Ichthyology since the publication
of the “Histoire naturelle” by Cuvier and Valenciennes, and the results
of the manifold enquiries were scattered over such a multitude of
publications, that it became imperative to collect again all these
materials in one comprehensive work. This was done in the “Catalogue
of Fishes,” published by the Trustees of the British Museum, in eight
volumes (Lond. 1859-70). Beside the species previously described
many new forms were added, the number total of species referred
to in those volumes amounting to 8525. As regards the systematic
arrangement--Müller’s system was adopted in the main, but the
definition of the families is much modified. This, however, need not be
further entered into here, and will become sufficiently apparent in the
subsequent parts of the present work.

  [Illustration: Fig. 1.--Lower aspect of head of _Raia
  lemprieri_.]




                              CHAPTER II.

      TOPOGRAPHICAL DESCRIPTION OF THE EXTERNAL PARTS OF FISHES.


[Sidenote: Form of the body.]

In the body of a fish four parts are distinguished: the _head_,
_trunk_, _tail_, and the _fins_; the boundary between the first and
second being generally indicated by the _gill-opening_, and that
between the second and third by the _vent_. The form of the body and
the relative proportions of those principal parts are subject to much
variation, such as is not found in any other class of Vertebrates.
In fishes which are endowed with the power of steady and more or
less rapid locomotion, a deviation from that form of body, which we
observe in a perch, carp, or mackerel, is never excessive. The body
forms a simple, equally-formed wedge, compressed or slightly rounded,
well fitted for cleaving the water. In fishes which are in the habit
of moving on the bottom, the whole body, or at least the head, is
_vertically depressed_ and flattened; the head may be so enormously
enlarged that the trunk and tail appear merely as an appendage. In
one family of fishes, the _Pleuronectidæ_ or Flat-fishes, the body is
compressed into a thin disk; they swim and move on one side only, which
remains constantly directed towards the bottom, a peculiarity by which
the symmetry of all parts of the body has been affected. A _lateral
compression_ of the body, in conjunction with a lengthening of the
vertical and a shortening of the longitudinal axis, we find in fishes
moving comparatively slowly through the water, and able to remain (as
it were) suspended in it. This deviation from the typical form may
proceed so far that the vertical axis greatly exceeds the longitudinal
in length; generally all the parts of the body participate in this
form, but in one kind of fish (the Sun-fish or _Orthagoriscus_) it is
chiefly the tail which has been shortened, and reduced so much as to
present the appearance of being cut off. An excessive lengthening of
the longitudinal axis, with a shortening of the vertical, occurs in
Eels and eel-like fishes, and in the so-called Band-fishes. They are
bottom-fish, capable of insinuating themselves into narrow crevices and
holes. The form of the body of these long fish is either cylindrical,
snake-like, as in the Eels and many Cod-fishes, or strongly compressed
as in the Band-fishes (_Trichiurus_, _Regalecus_, etc.) It is chiefly
the tail which is lengthened, but frequently the head and trunk
participate more or less in this form. Every possible variation
occurs between these and other principal types of form. The old
ichthyologists, even down to Linnæus, depended in great measure on them
for classification; but although often the same form of body obtains
in the same group of fishes, similarity of form by no means indicates
natural affinity; it only indicates similitude of habits and mode of
life.

[Sidenote: Eye.]

_The external parts of the Head._--The _Eye_ divides the head into the
_ante-orbital_ and _post-orbital_ portion. In most fishes, especially
in those with a compressed head, it is situated on the side and in the
anterior half of the length of the head; in many, chiefly those with a
depressed head, it is directed upwards, and sometimes situated quite
at the upper side; in very few, the eyes look obliquely downwards. In
the Flat-fishes both eyes are on the same side of the head, either the
right or the left, always on that which is directed towards the light,
and coloured.

Fishes in general, compared with other Vertebrata, have large eyes.
Sometimes these organs are enormously enlarged, their great size
indicating that the fish is either nocturnal, or lives at a depth to
which only a part of the sun’s rays penetrate. On the other hand, small
eyes occur in fishes inhabiting muddy places, or great depths to which
scarcely any light descends, or in fishes in which the want of an organ
of sight is compensated by the development of other organs of sense.
In a few fishes, more particularly in those inhabiting caves or the
greatest depths of the ocean, the eyes have become quite rudimentary
and hidden under the skin.

[Sidenote: Snout.]

In the _ante-orbital_ portion of the head, or the _Snout_, are situated
the mouth and the nostrils.

[Sidenote: Mouth.]

The _Mouth_ is formed by the intermaxillary and maxillary bones, or by
the intermaxillary only in the upper jaw, and by the mandibulary bone
in the lower. These bones are either bare or covered by integument, to
which frequently labial folds or lips are added. As regards form, the
mouth offers as many variations as the body itself, in accordance with
the nature of the food, and the mode of feeding. It may be narrow, or
extremely wide and cleft to nearly the hind margin of the head; it may
be semi-elliptical, semicircular, or straight in a transverse line;
it may be quite in front of the snout (_anterior_), or at its upper
surface (_superior_), or at its lower (_inferior_), or extending along
each side _(lateral_); sometimes it is subcircular, organised for
sucking. The jaws of some fishes are modified into a special weapon
of attack (Sword-fish, Saw-fish); in fact, throughout the whole class
of fishes the jaws are the only organ specialised for the purpose of
attacking; weapons on other parts of the body are purely defensive.

Both jaws may be provided with skinny appendages, _barbels_, which, if
developed and movable, are sensitive organs of touch.

[Sidenote: Nostrils.]

In the majority of fishes the _Nostrils_ are a double opening on
each side of the upper surface of the snout; the openings of each side
being more or less close together. They lead into a shallow groove;
and only in one family (the Myxinoids) perforate the palate. In this
family, as well as in the Lampreys, the nasal aperture is single. In
many Eels the openings are lateral, the lower perforating the upper
lip. In the Sharks and Rays (Fig. 1, p. 34) they are at the lower
surface of the snout, and more or less confluent; and, finally, in the
Dipnoi and other Ganoids, one at least is within the labial boundary of
the mouth.

The space across the forehead, between the orbits, is called the
_interorbital_ space; that below the orbit, the _infraorbital_ or
_sub-orbital_ region.

[Sidenote: Gill-cover.]

In the _post-orbital_ part of the head there are distinguished, at
least in most Teleosteous Fishes and many Ganoids, (Fig. 24) the
_præoperculum_, a sub-semicircular bone, generally with a free and
often serrated or variously-armed margin; the _operculum_, forming
the posterior margin of the gill-opening, and the _sub-operculum_
and _interoperculum_ along its inferior margin. All these bones,
collectively called _opercles_, form the _gill-cover_, a thin bony
lamella covering the cavity containing the gills. Sometimes they are
covered with so thin a membrane that the single bones may be readily
distinguished; sometimes they are hidden under a thick integument.
In some cases the interoperculum is rudimentary or entirely absent
(Siluroids).

[Sidenote: Gill-opening.]

The _Gill-opening_ is a foramen, or a slit behind or below the head,
by which the water which has been taken up through the mouth for the
purpose of breathing is again expelled. This slit may extend from
the upper end of the operculum all round the side of the head to the
symphysis of the lower jaw; or it may be shortened and finally reduced
to a small opening on any part of the margin of the gill-cover.
Sometimes (_Symbranchus_) the two openings, thus reduced, coalesce,
and form what externally appears as a single opening only. The margin
of the gill-cover is provided with a cutaneous fringe, in order to
more effectually close the gill-opening; and this fringe is supported
by one or several or many bony rays, the _branchiostegals_. The space
on the chest between the two rami of the lower jaw and between the
gill-openings is called the _isthmus_.

  [Illustration: Fig. 2.--Head of _Mordacia mordax_, showing
  the single nostril, and seven branchial openings.]

The Sharks and Rays differ from the Teleosteous and Ganoid fishes in
having five branchial slits (six or seven in _Hexanchus_ and
_Heptanchus_), which are lateral in the Sharks, and at the lower
surface of the head in the Rays (Fig. 1, p. 34). In Myxine only the
gill-opening is at a great distance from the head; it is either single
in this family (Cyclostomi), or there are six and more on each side
(Fig. 2).

[Sidenote: Tail.]

In the _Trunk_ are distinguished the _back_, the _sides_, and the
_abdomen_. It gradually passes in all fishes into the _Tail_; the
termination of the abdominal cavity and the commencement of the tail
being generally indicated by the position of the vent. The exceptions
are numerous: not only certain abdominal organs, like the sexual, may
extend to between the muscles of the tail, but the intestinal tract
itself may pass far backwards, or, singularly, it may be reflected
forwards, so that the position of the vent may be either close to the
extremity of the tail or to the foremost part of the trunk.

In many fishes the greater part of the tail is surrounded by the fins,
leaving only a small portion (between dorsal, caudal, and anal fins)
finless; this part is called the _free portion_ or the _peduncle_ of
the tail.

[Sidenote: Fins.]

The _Fins_ are divided into _vertical_ or _unpaired_, and into
_horizontal_ or _paired fins_. Any of them may be present or absent;
and their position, number, and form are most important guides in
determining the affinities of fishes.

The _vertical_ fins are situated in the median dorsal line, from the
head to the extremity of the tail, and in the ventral line of the
tail. In fishes in which they are least developed or most embryonic,
the vertical fin appears as a simple fold of the skin surrounding the
extremity of the tail In its further progress of development in the
series of fishes, it gradually extends more forwards, and may reach
even the head and vent. Even in this embryonic condition the fin is
generally supported by fine rays, which are the continuations of, or
articulated to, other stronger rays supported by the processes or
apophyses of the vertebral column. This form of the vertical fin is
very common, for instance in the Eels, many Gadoid, Blennioid and
Ganoid fishes in which, besides, the rays have ceased to be simple
rods, showing more or less numerous joints (simple _articulated_
rays; Fig. 3). _Branched_ rays are dichotomically split, the joints
increasing in number towards the extremity.

The continuity of the vertical fin, however, is interrupted in the
majority of fishes; and three fins then are distinguished: one in the
dorsal line--the _dorsal_ fin; one in the ventral line behind the
anus--the _anal_ fin; and one confined to the extremity of the
tail--the _caudal_ fin.

  [Illustration: Fig. 3.

    1. Simple ray.
    2. Spine.
    3. Simple articulated ray (soft).
    4. Branched ray (soft).]


The _caudal_ fin is rarely symmetrical, so that its upper half would
be equal to its lower; the greatest degree of asymmetry obtains
in fishes with heterocercal termination of the vertebral column
(see subsequently, Figs. 31, 41). In fishes in which it is nearly
symmetrical it is frequently prolonged into an upper and lower _lobe_,
its hind margin being concave or more or less deeply excised; in others
the hind margin is rounded, and when the middle rays greatly exceed in
length the outer ones the fin assumes a pointed form.

  [Illustration: Fig. 4.--Labrax lupus (Bass), an Acanthopterygian
  with anterior spinous, and posterior soft dorsal fin.]

Many and systematically important differences are observed
in the _dorsal_ fin, which is either spiny-rayed (spinous)
(_Acanthopterygian_), or soft-rayed (_Malacopterygian_). In the
former, a smaller or greater number of the rays are simple and without
transverse joints; they may be flexible, or so much osseous matter
is deposited in them that they appear hard and truly spinous (Fig.
3); these spines form always the anterior portion of the fin, which
is detached from, or continuous with, the remaining jointed rays.
The spines can be erected or depressed at the will of the fish; if
in the depressed position the spines cover one another completely,
their points lying in the same line, the fish is called _homacanth_;
but if the spines are asymmetrical, alternately broader on one side
than on the other, the fish is called _heteracanth_. The spinous
division, as well as the one consisting of jointed rays, may again
be subdivided. In the _Malacopterygian_ type all the rays remain
jointed; indeed, sometimes the foremost ray, with its preceding short
supports, is likewise ossified, and a hard spine, but the articulations
can nearly always be distinctly traced. Sometimes the dorsal fin of
Malacopterygian fishes is very long, extending from the head to the end
of the tail, sometimes it is reduced to a few rays only, and in a few
cases it is entirely absent. In addition to the rayed dorsal fin, many
Malacopterygian fishes (as the Salmonoids, many Siluroids, Scopeloids,
etc.) have another of greater or lesser extent, without any rays; and
as always fat is deposited within this fold, it is called a _fatty_ fin
(_pinna adiposa_).

  [Illustration: Fig. 5.--Saurus undosquamis, a Malacopterygian
  with anterior soft dorsal, and additional adipose fin.]

The _anal_ fin is built on the same plan as the dorsal, and
may be single or plural, long or short, or entirely absent; in
Acanthopterygians its foremost rays are frequently simple and spinous.

The _horizontal_ or _paired_ fins consist of two pairs: the pectorals
and ventrals.

The _pectoral_ fins (with their osseous supports) are the homologues of
the anterior limbs of the higher Vertebrata. They are always inserted
immediately behind the gill-opening; either symmetrical with a rounded
posterior margin, or asymmetrical, with the upper rays longest and
strongest; in Malacopterygians with a dorsal spine the upper pectoral
ray is frequently developed into a similar defensive weapon.

The _ventral_ fins are the homologues of the hind-limbs, and inserted
on the abdominal surface, either behind the pectorals (_Pisces_ s.
_Pinnæ abdominales_), or below them _(Pisces_ s. _Pinnæ thoracicæ_), or
in advance of them (_Pisces_ s. _Pinnæ jugulares_). They are generally
narrow, composed of a small number of rays, the outer of which is
frequently osseous. In some small groups of fishes, like the Gobies,
the fins coalesce and form a suctorial disk.

  [Illustration: Fig. 6.--Salmo salar (Salmon), with abdominal
  ventral fins.]

  [Illustration: Fig. 7.--Mullus barbatus (Red Mullet), with
  thoracic ventral fins.]

  [Illustration: Fig. 8.--Burbot (Lota vulgaris), with jugular
  ventral fins.]

For the definition of the smaller systematic groups, and the
determination of species, the numbers of the spines and rays are
generally of the greatest importance. This holds good, especially
for the ventral rays, by the number of which the Acanthopterygian
affinities of a fish can nearly always be determined. The numbers of
the dorsal and anal rays generally correspond to the number of vertebræ
in a certain portion of the spine, and are therefore constant specific,
generic, or even family characters; but when their number is very
great, a proportionally wide margin must be allowed for variation, and
the taxinomic value of this character becomes uncertain. The numbers of
the pectoral and caudal rays are rarely of any account.

[Sidenote: Function of the Fins.]

The fins are organs of motion; but it is chiefly the tail and the
caudal fin by which the fish impels itself forward. To execute
energetic locomotion the tail and caudal fin are strongly bent,
with rapidity, alternately towards the right and left; whilst a
gentle motion forwards is effected by a simple undulating action of
the caudal fin, the lobes of which act like the blades of a screw.
Retrograde motions can be made by fish in an imperfect manner only,
by forward-strokes of the pectoral fins. When the fish wants to
turn towards the left, he gives a stroke of the tail towards the
right, the right pectoral acting simultaneously, whilst the left
remains ad-pressed to the body. Thus the pectoral fins assist in the
progressive motions of the fish, but rather directing its course than
acting as powerful propellers. The chief function of the paired fins is
to maintain the balance of the fish in the water, which is always the
most unsteady where there is no weight to sink it: when the pectoral
of one side, or the pectoral and ventral of the same side are removed,
the fish loses its balance and falls on the side opposite; when both
pectorals are removed, the fish’s head sinks; on removal of the dorsal
and anal fins the motion of the fish assumes a zig-zag course. A fish
deprived of all fins, as well as a dead fish, floats with the belly
upwards, the back being the heavier part of the body.

In numerous groups of fishes which live in mud, or are enabled to pass
a longer or shorter time in soil periodically dried and hardened
during the hot season, forms occur entirely devoid of, or with only
rudimentary, ventral fins (Cyprinodon, Ophiocephalidæ, Galaxiidæ,
Siluridæ). The chief function of these fins being to balance the body
of the fish whilst swimming, it is evident that in fishes moving during
a great part of their life over swampy ground, or through more or less
consistent mud, this function of the ventral fins ceases, and that
nature can readily dispense with these organs altogether.

  [Illustration: Fig. 9.--Ventrals of _Gobius_.]

In certain fishes the shape and function of the fins are considerably
modified: thus, in the Rays, locomotion is almost entirely effected
and regulated by the broad and expanded pectoral fins acting with an
undulatory motion of their margins, similar to the undulations of the
long vertical fins of the Flat-fishes; in many Blennies the ventral
fins are adapted for walking on the sea-bottom; in some Gobioids
(_Periophthalmus_), Trigloids, Scorpænioids, and Pediculati, the
pectoral fins are perfect organs of walking; in the Gobies, Cyclopteri,
and Discoboli the ventral fins are transformed into an adhesive disk,
and finally in the Flying-fish, in which the pectorals act as a
parachute. In the Eels and other snake-like fishes, the swimming as
well as the gliding motions are effected by several curvatures of the
body, alternate towards the right and left, resembling the locomotion
of Snakes. In the _Syngnathi_ (Pipe-fishes) and _Hippocampi_,
whose body admits of but a slight degree of lateral curvature, and
whose caudal fin is generally small, if present at all, locomotion is
very limited, and almost wholly dependent on the action of the dorsal
fin, which consists of a rapid undulating movement.

  [Illustration: Fig. 10.--Cycloid scale of Gadopsis marmoratus
  (magn.)]

  [Illustration: Fig. 11.--Cycloid scale of Scopelus resplendens
  (magn.)]

[Sidenote: Skin and Scales.]

The _skin_ of fishes is either covered with scales, or naked, or
provided with more or less numerous scutes of various forms and sizes.
Some parts, like the head and fins, are more frequently naked than
scaly. All fishes provided with electric organs, the majority of Eels,
and the Lampreys, are naked. _Scales_ of fishes are very different from
those of Reptiles; the latter being merely folds of the cutis, whilst
the scales of fishes are distinct horny elements, developed in grooves
or pockets of the skin, like hairs, nails, or feathers. Very small
or rudimentary scales are extremely thin, homogeneous in structure,
and more or less imbedded in the skin, and do not cover each other.
When more developed, they are imbricated (arranged in the manner of
tiles), with the posterior part extruded and free, the surface of the
anterior portion being usually covered by the skin to a greater or less
extent. On their surface (Figs. 10 and 11) may be observed a very fine
striation concentric and parallel to the margin, and coarser striæ
radiating from a central point towards the hind margin. Scales without
a covering of enamel, with an entire (not denticulated) posterior
margin, and with a concentric striation, are called _Cycloid_ scales.
_Ctenoid_ scales (Figs. 12–15) are generally thicker, and provided
with spinous teeth on the posterior edges of the layers of which the
scale consists. In some species only the layer nearest to the margin
is provided with denticulations (Fig. 14). Scales, the free surface of
which is spiny, and which have no denticulation on the margin, have
been termed _Sparoid_ scales; but their distinction from ctenoid scales
is by no means sharp, and there are even intermediate forms between
the cycloid and ctenoid types. Both kinds of scales may occur not only
in species of the same genus of fishes, but in the same fish.

  [Illustration: Fig. 12.--Ctenoid scale of Scatophagus
  multifasciatus (magn.)]

  [Illustration: Fig. 13.--Ctenoid scale of Platycephalus
  cirrhonasus (magn.)]

  [Illustration: Fig. 14.--Ctenoid scale of Gobius ommaturus
  (magn.)]

  [Illustration: Fig. 15.--Ctenoid scale of Lethrinus (magn.)]

  [Illustration: Fig. 16. Ganoid Scales.]

_Ganoid_ scales are hard and bony, covered with a layer of enamel; they
are generally rhombic or quadrangular, rarely rounded and imbricate;
and arranged in oblique rows, those of one row being linked together
by an articulary process. This type of scales, common in fossil Ganoid
fishes, occurs among recent fishes in _Lepidosteus_ and _Polypterus_
only.

Finally, in Sharks, the Balistidæ, and others, true scales are absent
and replaced by the ossified papillæ of the cutis, which give the
surface the appearance of fine-grained chagreen. These generally small
bodies, as well as the large osseous scutes of the Rays, Sturgeons,
etc., have been comprised under the common name _Placoid_ scales; a
term which deservedly is being abandoned.

  [Illustration: Fig. 17.--Dermal papillæ of Monacanthus trossulus.]

  [Illustration: Fig. 18.--Dermal papillæ of Monacanthus
  hippocrepis (magn.)]

  [Illustration: Fig. 19.--Cycloid scale from the lateral line of
  Odax lineatus (magn.)]

Along the side of the body of osseous fishes runs a series of
perforated scales, which is called the _lateral line_ (Fig. 21).
The perforating duct is simple at its base, and may be also simple at
its outer opening (Fig. 19), or (and this is frequently the case) the
portion on the free surface of the scale is ramified (Fig. 20). The
lateral line runs from the head to the tail, sometimes reaching the
caudal fin, sometimes stopping in front of it, sometimes advancing over
its rays. It is nearer to the dorsal profile in some fishes than in
others. Some species have several lateral lines, the upper one coasting
the dorsal, the lower the abdominal outline, one running along the
middle as usual. The scales of the lateral line are sometimes larger
than the others, sometimes smaller, sometimes modified into scutes,
sometimes there are no other scales beside them, the rest of the body
being naked. The foramina of the lateral line are the outlets of a
muciferous duct which is continued on to the head, running along the
infraorbital bones, and sending off a branch into the præopercular
margin and mandible. In many fishes, as in many Sciænoids, Gadoids,
and in numerous deep-sea fishes, the ducts of this muciferous system
are extraordinarily wide, and generally filled with mucus, which
is congealed or contracted in specimens preserved in spirits, but
swells again when the specimens are immersed in water. This system is
abundantly provided with nerves, and, therefore, has been considered
to be the seat of a sense peculiar to fishes, but there cannot be any
doubt that its function is the excretion of mucus, although probably
mucus is excreted also from the entire surface of the fish.

  [Illustration: Fig. 20.--Cycloid scale from the lateral line of
  Labrichthys laticlavius (magn.)]

The scales, their structure, number and arrangement, are an important
character for the determination of fishes; in most scaly fishes they
are arranged in oblique transverse series; and as the number of scales
in the lateral line generally corresponds to the number of transverse
series, it is usual to count the scales in that line. To ascertain
the number of longitudinal series of scales, the scales are counted
in one of the transverse series, generally in that running from the
commencement of the dorsal fin, or the middle of the back to the
lateral line, and from the lateral line down to the vent or ventral
fin, or middle of the abdomen.[4]

  [Illustration: Fig. 21.--Arrangement of scales in the Roach
  (Leuciscus ratilus): _Ll_ = Lateral line; _tr_ =
  Transverse line. _a_, Transverse line from lateral line to
  ventral fin.]

The scales of many fishes are modified for special purposes, especially
to form weapons of defence or a protective armour, but the details of
such modifications are better mentioned under the several families in
which they occur. All scales are continually growing and wasting away
on the surface, and it seems that some fish, at least,--for instance,
Salmonoids--“shed” them periodically; during the progress of this
shedding the outlines of the scales are singularly irregular.




                             CHAPTER III.

              TERMINOLOGY AND TOPOGRAPHY OF THE SKELETON.


In order to readily comprehend the subsequent account of the
modifications of the skeleton in the various sub-classes and groups of
Fishes, the student has to acquaint himself with the terms used for the
numerous bones of the fish skeleton, as well as with their relative
position. The skeleton of any of the more common kinds of osseous fish
may serve for this purpose; that of the Perch is chosen here.

The series of bones constituting the axis of the body, and destined to
protect the spinal chord and some large longitudinal blood-vessels, is
called the _vertebral_ or _spinal column_; the single bones are the
_vertebræ_. The _skull_ consists of the bones surrounding the brain
and organs of sense, and of a number of arches suspended from it, to
support the commencement of the alimentary canal and the respiratory
organs.

The _vertebra_ (Fig. 22) consists of a body or _centrum_ (_c_), with
a concave anterior and posterior surface, and generally of several
_processes_ or _apophyses_, as--1. Two _neurapophyses_ (_na_), which,
on the dorsal side, rising upwards, form the _neural arch_ over the
canal, in which the spinal chord is lodged. 2. Two _parapophyses_
(_pa_) usually projecting from the lower part of the sides of the body,
or two _hæmapophyses_ (_ha_) which actually coalesce to form on the
ventral side the hæmal canal for a large trunk of the vascular system.
3. A _neural spine_ (_ns_), which crowns the neurapophyses, or is
interposed between their tips. 4. A _hæmal spine_ (_hs_), having the
same relation to the hæmapophyses. 5. Two _pleurapophyses_ or floating
_ribs_, suspended from, or from the base of, the parapophyses. 6. In
most fishes the neural arches are connected together by articular or
oblique processes, _zygapophyses_ (_za_), which are developed from the
base of each neurapophysis.

  [Illustration: Fig. 22.--Side and Front view of Fish-vertebra.]

The vertebræ are either _abdominal_ or _caudal_ vertebræ, the
coalescence of the parapophyses into a complete hæmal ring, and the
suspension of the anal fin generally forming a sufficiently well-marked
boundary between abdominal and caudal regions (Fig. 23). In the Perch
there are twenty-one abdominal and as many caudal vertebræ. The centrum
of the first vertebra or atlas is very short, with the apophyses
scarcely indicated, and lacking ribs like the succeeding vertebra. All
the other abdominal vertebræ, with the exception of the last or two
last, are provided with ribs, many of which are bifid (72). A series of
flat spines (74), called _interneurals_, to which the spines and rays
of the dorsal fins are articulated, are supported by the neural spines,
the strength of the neurals and interneurals corresponding to that of
the _dermal_ spines (75). The caudal vertebræ differ from the abdominal
in having the hæmapophyseal elements converted into spines similar to
the neurals, the anterior being likewise destined to support a series
of _interhæmals_ (79), to which the anal rays are articulated. The
last and smallest caudal vertebra articulates with the _hypural_ (70),
a fan-like bone, which, together with the dilated hindmost neural and
hæmal elements, supports the caudal rays.

Looking at a perch’s _skull_ from the side (Fig. 24), the most
superficial bones will be found to be those of the jaws, a chain of
thin bones round the lower half of the eye, and the opercles.

The anterior margin of the upper jaw is formed by the _intermaxillary_
or _premaxillary_ (17) which bears teeth, terminates in a pedicle
above, to allow of a forward sliding motion of the jaw, and is dilated
into a flat triangular process behind, on which leans the second
bone of the upper jaw, the _maxillary_ (18). This bone is toothless,
articulates with the vomer and palatine bone, and is greatly dilated
towards its distal extremity. Both the maxillary and intermaxillary
lie and move parallel to each other, being connected by a narrow
membrane; in many other fishes their relative position is very
different.

The _mandible_ or lower jaw consists of a right and left ramus;
their union by a ligament in front is called _symphysis_. Each ramus
is formed of several pieces; that which, by a sigmoid concavity
articulates with the quadrate, is the _articulary_ bone (35); it sends
upwards a coronoid process, to which a ligament from the maxillary
and the masticatory muscles are attached; and forwards a long-pointed
process, to be sheathed in the deep notch of the anterior piece. A
small separate piece (36) at the lower posterior angle of the mandible
is termed _angular_. The largest piece (34) is tooth-bearing, and hence
termed _dentary_; at its inner surface it is always deeply excavated,
to receive a cylindrical cartilage, called _Meckel’s cartilage_, the
remains of an embryonic condition of the jaw, the articulary and
angular being but ossified parts of it. In other _Teleostei_ this
number is still more increased by a _splenial_ and other bones.

The _infraorbital_ ring of bones (Fig. 23, ^{19}) consists of several
(four) pieces, of which the anterior is the largest, and distinguished
as _præorbital_.

The so-called _præoperculum_ (30) belongs rather to the bones of the
suspensorium of the mandible, presently to be described, than to the
opercles proper. It is narrow, strong, angularly bent, so as to consist
of a vertical and horizontal limb, with an incompletely closed canal
running along both limbs. As it is quite a superficial bone, and
frequently armed with various spines, its form and configuration form
an important item in the descriptive details of many fishes.

The principal piece of the gill-cover is the _operculum_ (28),
triangular in shape, situated behind, and movably united with, the
vertical limb of the præoperculum. There is an articulary cavity at
its upper anterior angle for its junction with the hyomandibular. The
oblong lamella below the operculum is the _sub-operculum_ (32), and
the one in front of this latter, below the horizontal limb of the
præoperculum, is the _interoperculum_ (33), which is connected by
ligament with the angular piece of the lower jaw, and is also attached
to the outer face of the hyoid, so that the gill-covers cannot open or
shut without the hyoid apparatus executing a corresponding movement.

The chain of flat bones which, after the removal of the temporal
muscles, appear arranged within the inner concavity of the præoperculum
(Fig. 24), are comprised with the latter under the common name of
_mandibulary suspensorium_. They connect the mandible with the
cranium. The uppermost, the _epitympanic_ or _hyomandibular_ (23), is
articulated by a double articulary head with the mastoid and posterior
frontal. Another articulary head is destined for the opercular joint.
The _mesotympanic_ or _symplectic_ (31) appears as a styliform
prolongation of the lower part of the hyomandibular; is entirely
cartilaginous in the young, but nearly entirely ossified in the adult.
The position of this bone is noteworthy, because, directly inwards of
its cartilaginous junction with the hyomandibular, there is situated
the uppermost piece of the hyoid arch, the stylohyal. The next bone of
the series is the _pretympanic_ or _metapterygoid_ (27), a flat bone
forming a bridge towards the pterygoid, and not rarely absent in the
teleosteous sub-class. Finally, the large triangular _hypo-tympanic_ or
_quadrate_ (26) has a large condyle for the mandibulary joint.

The palatine arch (Fig. 26) connects the suspensorium with the
anterior extremity of the skull, and is formed by three bones: the
_entopterygoid_ (25), an oblong and thin bone attached to the inner
border of the palatine and pterygoid, and increasing the surface of
the bony roof of the mouth towards the median line; it constitutes
also the floor of the orbit. The _pterygoid_ (24) (or _os transversum_)
starts from the quadrate, and is joined by suture to the _palatine_,
which is toothed, and reaches to the vomer and anterior frontal.

In the occipital region there are distinguished the _basi-occipital_
(5), readily recognised by the conical excavation corresponding and
similar to that of the atlas, with which it is articulated through
the intervention of a capsule filled with a gelatinous substance (the
remains of the notochord); the _exoccipitals_ (10), articulated, one on
each side, to the basi-occipital, and expanding on the upper surface of
that bone, so as to meet and support the spinal column; a superficial
thin lamella (13), suturally connected with the exoccipitals,
not constant in fishes, and erroneously believed by Cuvier to be
the _petrosal_ (_os petrosum_) of higher animals; further, the
_paroccipitals_ (9), which are wedged in between the exoccipitals and
_supraoccipital_. This last bone (8) forms the key of the arch over the
occipital foramen, and raises a strong high crest from the whole length
of its mesial line; a transverse supraoccipital ridge, coming from each
side of the base of this spine runs outwards laterally to the external
angles of the bone. The supraoccipital separates the parietals, and
forms a suture with the frontals.

In front of the basi-occipital the base of the skull is formed by the
_basisphenoid_ (_parasphenoid_ of Huxley) (6). This very long and
narrow bone extends from the basi-occipital beyond the brain-capsule to
between the orbits, where it forms the support of the fibro-membranous
interorbital septum. Anteriorly it is connate with another long
hammer-shaped bone (16), the _vomer_, the head of which marks the
anterior end of the palate, and is beset with teeth. The _alisphenoids_
(11) are short broad bones, rising from the basisphenoid; their
posterior margins are suturally connected with the anterior of the
basi- and exoccipitals.

  [Illustration: Fig. 23.--Skeleton of the Perch.]

  [Illustration: Fig. 24.--Skeleton of a Perch’s Skull.]

  [Illustration: Fig. 25.--Hyoid arch, branchial apparatus, and
  scapulary arch of the Perch.]

  [Illustration: Fig. 26.--Lower view of Skull of Perch.]

  [Illustration: Fig. 27.--Hyoid bone of the Perch.]

The formation of the posterior part of the side of the skull is
completed by the _mastoid_ and _parietal_ bones. The former (12)
projects outwards and backwards farther than the paroccipital, forming
the outer strong process of the side of the cranium. This process
lodges on its upper surface one of the main ducts of the muciferous
system, and affords the base of articulation to a part of the
hyomandibular. Its extremity gives attachment to the strong tendon of
the dorso-lateral muscles of the trunk. The _parietals_ (7) are flat
bones, of comparatively much smaller extent than in higher Vertebrates,
and separated from each other by the anterior prolongation of the
supraoccipital.

The anterior wall of the brain-capsule (or the posterior of the orbit)
is formed by the _orbitosphenoids_ (14), between which, superiorly,
the olfactory nerves, and inferiorly, the optic, pass out of the
cranium. In addition to this paired bone, the Perch and many other
fishes possess another single bone (15),--the _os sphenoideum anterius_
of Cuvier, _ethmoid_ of Owen, and _basisphenoid_ of Huxley; it is
Y-shaped, each lateral branch being connected with an orbito-sphenoid,
whilst the lower branch rests upon the long basal bone.

A cartilage, the substance of which is thickest above the vomer,
and which extends as a narrow stripe along the interorbital septum,
represents the _ethmoid_ of higher Vertebrata; the olfactory nerves run
along, and finally perforate it.

There remain, finally, the bones distinguishable on the upper surface
of the skull; the largest, extending from the nasal cavities to the
occipital, are the _frontal_ bones (1), which also form the upper
margin of the orbit. The _postfrontals_ (4) are small bones placed
on the supero-posterior angle of the orbit, and serving as the point
from which the infraorbital ring is suspended. The _pre-frontals_ (2),
also small, occupy the anterior margin of the orbit. A pair of small
tubiform bones (20), the _turbinals_, occupy the foremost part of the
snout, in front of the frontals, and are separated from each other by
intervening cartilage.

After removal of the gill-cover and mandibulary suspensorium, the hyoid
arch, which encloses the branchial apparatus, and farther behind,
the humeral arch are laid open to view (Fig. 25). These parts can be
readily separated from the cranium proper.

The _hyoid arch_ is suspended by a slender styliform bone, the
_stylohyal_ (29), from the hyomandibulars; it consists of three
segments, the _epihyal_ (37), _ceratohyal_ (38), which is the longest
and strongest piece, and the _basihyal_, which is formed by two
juxtaposed pieces (39, 40). Between the latter there is a median
styliform ossicle (41), extending forwards into the substance of the
tongue, called _glossohyal_ or _os linguale_; and below the junction of
the two hyoid branches there is a vertical single bone (42), expanded
along its lower edge, which, connected by ligament with the anterior
extremity of the humeral arch, forms the _isthmus_ separating the
two gill-openings. This bone is called the _urohyal_. Articulated or
attached by ligaments to the epihyal and ceratohyal are a number of
sword-shaped bones or rays (43), the _branchiostegals_, between which
the branchiostegal membrane is extended.

The _branchial arches_ (Figs. 25 and 27) are enclosed within the hyoid
arch, with which they are closely connected at the base. They are five
in number, of which four bear gills, whilst the fifth (56) remains
dwarfed, is beset with teeth, and called the _lower pharyngeal_ bone.
The arches adhere by their lower extremities to a chain of ossicles
(53, 54, 55), _basibranchials_, and, curving as they ascend, nearly
meet at the base of the cranium, to which they are attached by a
layer of ligamentous and cellular tissue. Each of the first three
branchial arches consists of four pieces movably connected with one
another. The lowest is the _hypobranchial_ (57), the next much longer
one (58) the _cerato-branchial_, and, above this, a slender and a
short irregularly-shaped _epibranchial_ (61). In the fourth arch
the hypobranchial is absent. The uppermost of these segments (62),
especially of the fourth arch, are dilated, and more or less confluent;
they are beset with fine teeth, and generally distinguished as the
_upper pharyngeal bones_. Only the cerato-branchial is represented in
the fifth arch or lower pharyngeal. On their outer convex side the
branchial segments are grooved for the reception of large blood-vessels
and nerves; on the inner side they support horny processes (63), called
the _gill-rakers_, which do not form part of the skeleton.

The _scapular_ or _humeral arch_ is suspended from the skull by the
(_suprascapula_) _post-temporal_ (46), which, in the Perch, is attached
by a triple prong to the occipital and mastoid bones. Then follows the
(_scapula_) _supraclavicula_ (47), and the arch is completed below
by the union of the large (_coracoid_) _clavicula_ (48) with its
fellow. Two flat bones (51, 52), each with a vacuity, attached to the
clavicle have been determined as the (_radius_ and _ulna_) _coracoid_
and _scapula_ of higher vertebrates, and the two series of small
bones (53) intervening between the forearm and the fin as _carpals_
and _metacarpals_. A two-jointed appendage the (_epicoracoid_)
_postclavicula_, is attached to the clavicle: its upper piece (49) is
broad and lamelliform, its lower (50) styliform and pointed.

The ventral fins are articulated to a pair of flat triangular bones,
the _pubic_ bones (80).

The bones of the skull of the fish have received so many different
interpretations that no two accounts agree in their nomenclature,
so that their study is a matter of considerable difficulty to the
beginner. The following synonymic table will tend to overcome
difficulties arising from this cause; it contains the terms used
by Cuvier, those introduced by Owen, and finally the nomenclature
of Stannius, Huxley, and Parker. Those adopted in the present work
are printed in italics. The numbers refer to the figures in the
accompanying woodcuts (Figs. 23–27).

        _Cuvier._          _Owen._             _Stannius._       _Huxley, Parker,
                                                                       etc._

  1. Frontal principal   _Frontal_           Os frontale
  2. Frontal antérieur   _Prefrontal_        Os frontale         Lateral ethmoid
                                               anterius            (Parker)
  3. _Ethmoid_             Nasal             Os ethmoideum
  4. Frontal              _Postfrontal_      Os frontale         Sphenotic
       postérieur                              posterius           (Parker)
  5. Basilaire            _Basioccipital_    Os basilare
  6. Sphénoide            _Basisphenoid_     Os sphenoideum      Sometimes referred
                                               basilare            to as “_Basal_”
  7. Pariétal             _Parietal_         Os parietale
  8. Interpariétal or     _Supraoccipital_   Os occipitale
       occipital                               superius
       supérieure
  9. Occipital externe    _Paroccipital_     Os occipitale       Epioticum
                                               externum            (Huxley)
 10. Occipital lateral    _Exoccipital_      Os occipitale
                                               laterale
 11. Grande aile du       _Alisphenoid_      Ala temporalis      Prooticum
       sphénoide                                                   (_Huxley_)
 12. Mastoidien           _Mastoid_          Os mastoideum       {
                                             + os extrascapulare {Opisthoticum[5]
                                                                 {  +_Squamosal_
 13. Rocher               Petrosal and       Oberflächliche      {  (Huxley)
                            Otosteal           Knochen-lamelle   {
 14. Aile orbitaire       _Orbitosphenoid_   Ala orbitalis       Alisphenoid
                                                                   (Huxley)
 15. Sphenoide            Ethmoid and        Os sphenoideum      _Basisphenoid_
       antérieur            Ethmoturbinal      anterius            (Huxley)
 16. _Vomer_              Vomer              Vomer
 17. Intermaxillaire      _Inter- or Pre-    Os intermaxillare
                            maxillary_
 18. Maxillaire           _Maxillary_        Os maxillare
       supérieur
 19. Sousorbitaires       _Infraorbital      Ossa
                            ring_              infraorbitalia
 20. Nasal                _Turbinal_         Os terminale
 22. Palatine             _Palatin_          Os palatinum
 23. Temporal             Epitympanic        Os temporale        _Hyomandibular_
                                                                   (Huxley)
 24. Transverse           _Pterygoid_        Os transversum
                                               s. pterygoideum
                                               externum
 25. Ptérygoidien         _Entopterygoid_    Os pterygoideum     Mesopterygoid
        interne                                                    (Parker)
 26. Jugal                Hypotympanic       Os quadratojugale   _Quadrate_
                                                                   (Huxley)
 27. Tympanal             Pretympanic        Os tympanicum       _Metapterygoid_
                                                                   (Huxley)
 28. Operculaire          _Operculum_        Operculum
 29. Styloide             _Stylohyal_        Os styloideum
 30. Préopercule          _Præoperculum_     Præoperculum
 31. Symplectique         Mesotympanic       _Os symplecticum_
 32. Sousopercule         _Suboperculum_     Suboperculum
 33. Interopercule        _Interoperculum_   Interoperculum
 34. Dentaire             _Dentary_          Os dentale
 35. Articulaire          _Articulary_       Os articulare
 36. Angulaire            _Angular_          Os angulare
 37. } Grandes pièces     _Epihyal_         }
 38. }   latérales        _Ceratohyal_      } Segmente der
                                            }   Zungenbein-
 39. } Petites pièces     _Basihyal_        }   Schenkel
 40. }   laterales                          }
 41. Os lingual           _Glossohyal_       Os linguale s.
                                               entoglossum
 42. Queue de l’os hyoide _Urohyal_                              Basibranchiostegal
                                                                      (Parker)
 43. Rayon branchiostège  _Branchiostegal_   Radii branchio-
                                               stegi
 46. Surscapulaire        Suprascapula       Omolita             _Post-temporal_
                                                                    (Parker)
 47. Scapulaire           Scapula            Scapula             _Supraclavicula_
                                                                    (Parker)
 48. Humeral              Coracoid           Clavicula           _Clavicula_
                                                                    (Parker)
 49. } Coracoid           Epicoracoid                            _Postclavicula_
 50. }                                                              (Parker)
 51. Cubital              Radius            } Ossa carpi         _Coracoid_ (Parker)
 52. Radial               Ulna              }                    _Scapula_ (Parker)
 53. Os du carpe          _Carpals_          Ossa metacarpi    { _Basalia_ (Huxley),
                                                               { Brachials (Parker)
 53 bis. }
 54.     } Chaine intermédiaire _Basibranchials_  Copula
 55.     }
 56. Pharyngiens          _Lower_            Ossa pharyngea
      inférieurs            _Pharyngeals_      inferiora
 57. Pièce interne de     _Hypobranchial_        }
      partie inférieure                          }
      de l’arceau                                }
      branchiale                                 }
 58. Pièce externe  „     _Ceratobranchial_      } Segmente der
 59. Stylet de prémière   _Upper epibranchial_   }   Kiemenbogen-
       arceau branchiale    _of first branchial_ }   Schenkel
                            _arch_               }
 61. Partie supérieure    _Epibranchials_        }
        de l’arceau                              }
        branchiale                               }
 62. Os pharyngian        Pharyngo-          Os pharyngeum       _Upper pharyngeals_
       supérieur            branchial          superius
 63.                      _Gill-rakers_
 65. Rayons de la         _Pectoral rays_    Brustflossen-
       pectorale                               Strahlen
 67, 68. Vertèbres        _Abdominal         Bauchwirbel
           abdominales      vertebræ_
 69. Vertèbres caudales   _Caudal vertebræ_  Schwanzwirbel

 70. Plaque triangulaire  [Aggregated        Verticale Platte    _Hypural_(Huxley)
        et verticale           interhæmals]
 71.                       _Caudal rays_     Schwanzflossen
                                               Strahlen
 72. Côte                  _Rib_             Rippen
 73. Appendices or        _Epipleural        Muskel-Gräthen
       stylets              spines_
 74. Interépineux         _Interneural       Ossa interspinalia
                            spines_            s. obere
                                               Flossentræger
 75. Épines et rayons     _Dorsal rays and_  Rückenflossen-Strahlen
           dorsales         _spines_           u. Stacheln
 76.                      _First
                            interneural_
 78.                      _Rudimentary_
                             _caudal rays_
 79. Apophyses épineuses  _Interhæmal        Untere Flossentræger
           inférieures      spines_
 80.                      _Pubic_            Becken
 81.                      _Ventral spine_    Bauchflossen-Stachel




                              CHAPTER IV.

                    MODIFICATIONS OF THE SKELETON.


The lowermost sub-class of fishes, which comprises one form only, the
Lancelet (_Branchiostoma_ [s. _Amphioxus_] _lanceolatum_), possesses
the skeleton of the most primitive type.

  [Illustration: Fig. 28.--Branchiostoma lanceolatum. _a_,
  Mouth; _b_, Vent; _c_, abdominal porus.]

  [Illustration: Fig. 29.--Anterior end of body of Branchiostoma
  (magn.) _d_, Chorda dorsalis; _e_, Spinal chord; _f_,
  Cartilaginous rods; _g_, Eye; _h_, Branchial rods; _i_, Labial
  cartilage; _k_, Oral cirrhi.]

The vertebral column is represented by a simple _chorda_ _dorsalis_
or _notochord_ only, which extends from one extremity of the fish to
the other, and, so far from being expanded into a cranial cavity,
it is pointed at its anterior end as well as at its posterior. It is
enveloped in a simple membrane like the spinal chord and the abdominal
organs, and there is no trace of vertebral segments or ribs; however, a
series of short cartilaginous rods above the spine evidently represent
apophyses. A maxillary or hyoid apparatus, or elements representing
limbs, are entirely absent.

   [J. Müller, Ueber den Bau und die Lebenserscheinungen des
   _Branchiostoma lubricum_, in Abhandl. Ak. Wiss. Berlin,
   1844.]

The skeleton of the _Cyclostomata_ (or Marsipobranchii) (Lampreys and
Sea-hags) shows a considerable advance of development. It consists of
a notochord, the anterior pointed end of which is wedged into the base
of a cranial capsule, partly membranous partly cartilaginous. This
skull, therefore, is not movable upon the spinal column. No vertebral
segmentation can be observed in the notochord, but neural arches are
represented by a series of cartilages on each side of the spinal chord.
In _Petromyzon_ (Fig. 30) the basis cranii emits two prolongations on
each side: an inferior, extending for some distance along the lower
side of the spinal column, and a lateral, which is ramified into a
skeleton supporting the branchial apparatus. A stylohyal process and a
subocular arch with a palato-pterygoid portion may be distinguished.
The roof of the cranial capsule is membranous in _Myxine_ and in the
larvæ of _Petromyzon_, but more or less cartilaginous in the adult
_Petromyzon_ and in _Bdellostoma_. A cartilaginous capsule on each side
of the hinder part of the skull contains the auditory organ, whilst the
olfactory capsule occupies the anterior upper part of the roof. A broad
cartilaginous lamina, starting from the cranium and overlying part
of the snout, has been determined as representing the ethmo-vomerine
elements, whilst the oral organs are supported by large, very peculiar
cartilages (_labials_), greatly differing in general configuration
and arrangement in the various Cyclostomes. There are three in the
Sea-lamprey, of which the middle one is joined to the palate by an
intermediate smaller one; the foremost is ring-like, tooth-bearing,
emitting on each side a styliform process. The lingual cartilage is
large in all Cyclostomes.

There is no trace of ribs or limbs.

   [J. Müller, Vergleichende Anatomie der Myxinoiden. Erster Theil.
   Osteologie und Myologie, in Abhandl. Ak. Wiss. Berlin, 1835.]

  [Illustration: Fig. 30.--Upper (A) and side (B) views, and
  vertical section (C) of the skull of _Petromyzon marinus_.

    _a_, Notochord; _b_, Basis cranii; _c_, Inferior, and _d_,
    Lateral process of basis; _e_, Auditory capsule; _f_,
    Subocular arch; _g_, Stylohyal process; _h_, Olfactory
    capsule; _i_, Ethmo-vomerine plate; _k_, Palato-pterygoid
    portion of subocular arch; _l-n_, Accessory labial or rostral
    cartilages; with _o_, appendage; _p_, lingual cartilage;
    _q_, neural arches; _r_, Branchial skeleton; _s_, Blind
    termination of the nasal duct between the notochord and
    œsophagus.]

  [Illustration: Fig. 31.--Heterocercal Tail of Centrina salviani.
  _a_, Vertebræ; _b_, Neurapophyses; _c_,
  Hæmapophyses.]

The _Chondropterygians_ exhibit a most extraordinary diversity in
the development of their vertebral column; almost every degree of
ossification, from a notochord without a trace of annular structure to
a series of completely ossified vertebræ being found in this order.
Sharks, in which the notochord is persistent, are the _Holocephali_
(if they be reckoned to this order, and the genera _Notidanus_ and
_Echinorhinus_). Among the first, _Chimæra monstrosa_ begins to show
traces of segmentation; but they are limited to the outer sheath of the
notochord, in which slender subossified rings appear. In _Notidanus_
membranous septa, with a central vacuity, cross the substance of the
gelatinous notochord. In the other Sharks the segmentation is complete,
each vertebra having a deep conical excavation in front and behind,
with a central canal through which the notochord is continued; but the
degree in which the primitive cartilage is replaced by concentric or
radiating lamellæ of bone varies greatly in the various genera, and
according to the age of the individuals. In the Rays all the vertebræ
are completely ossified, and the anterior ones confluent into one
continuous mass.

In the majority of Chondropterygians the extremity of the vertebral
column shows a decidedly heterocercal condition (Fig. 31), and only a
few, like _Squatina_ and some Rays, possess a diphycercal tail

The advance in the development of the skeleton of the Chondropterygians
beyond the primitive condition of the previous sub-classes, manifests
itself further by the presence of neural and hæmal elements, which
extend to the foremost part of the axial column, but of which the hæmal
form a closed arch in the caudal region only, whilst on the trunk they
appear merely as a lateral longitudinal ridge.

  [Illustration: Fig. 32. Fig. 33. Fig. 34.

  Fig. 32.--Lateral view. Fig. 33.--Longitudinal section. Fig.
  34.--Transverse section of Caudal vertebra of Basking Shark
  (Selache maxima). (After Hasse.) _a_, Centrum; _b_,
  Neurapophysis; _c_, Intercrural cartilage; _d_,
  Hæmapophysis; _e_, Spinal canal; _f_, Intervertebral
  cavity; _g_, Central canal for persistent portion of
  notochord; _h_, Hæmal canals for blood-vessels.]

The neural and hæmal apophyses are either merely attached to the
axis, as in Chondropterygians with persistent notochord, the Rays
and some Sharks; or their basal portions penetrate like wedges into
the substance of the centrum, so that, in a transverse section, in
consequence of the difference in their texture, they appear in the
form of an X.[6] The interspaces between the neurapophyses of the
vertebræ are not filled by fibrous membrane, as in other fishes, but
by separate cartilages, _laminæ_ or _cartilagines intercrurales_, to
which frequently a series of terminal pieces is superadded, which
must be regarded as the first appearance of the interneural spines
of the Teleostei and many Ganoids. Similar terminal pieces are
sometimes observed on the hæmal arches. _Ribs_ are either absent or but
imperfectly represented (_Carcharias_).

The substance of the _skull_ of the Chondropterygians is cartilage,
interrupted especially on its upper surface by more or less extensive
fibro-membranous fontanelles. Superficially it is covered by a more or
less thick chagreen-like osseous deposit. The articulation with the
vertebral column is effected by a pair of lateral condyles. In the
Sharks, besides, a central conical excavation corresponds to that of
the centrum of the foremost vertebral segment, whilst in the Rays this
central excavation of the skull receives a condyle of the axis of the
spinous column.

The cranium itself is a continuous undivided cartilage, in which the
limits of the orbit are well marked by an anterior and posterior
protuberance. The ethmoidal region sends horizontal plates over
the nasal sacs, the apertures of which retain their embryonic
situation upon the under surface of the skull. In the majority of
Chondropterygians these plates are conically produced, forming the base
of the soft projecting snout; and in some forms, especially in the
long-snouted Rays and the Saw-fishes (_Pristis_) this prolongation
appears in the form of three or more tubiform rods.

As separate cartilages there are appended to the skull a suspensorium,
a palatine, mandible, hyoid, and rudimentary maxillary elements.

The suspensorium is movably attached to the side of the skull. It
generally consists of one piece only, but in some Rays of two. In the
Rays it is articulated with the mandible only, their hyoid possessing
a distinct point of attachment to the skull. In the Sharks the hyoid
is suspended from the lower end of the suspensorium together with the
mandible.

What is generally called the upper jaw of a Shark is, as Cuvier has
already stated, not the maxillary, but palatine. It consists of two
simple lateral halves, each of which articulates with the corresponding
half of the lower jaw, which is formed by the simple representative of
Meckel’s cartilage.

Some cartilages of various sizes are generally developed on each side
of the palatine, and one on each side of the mandible. They are called
_labial_ cartilages, and seem to represent maxillary elements.

The _hyoid_ consists generally of a pair of long and strong lateral
pieces, and a single mesial piece. From the former cartilaginous
filaments (representing branchiostegals) pass directly outwards.
Branchial arches, varying in number, and similar to the hyoid, succeed
it. They are suspended from the side of the foremost part of the
spinous column, and, like the hyoid, bear a number of filaments.

The vertical fins are supported by interneural and interhæmal
cartilages, each of which consists of two and more pieces, and to which
the fin-rays are attached without articulation.

The _scapular arch_ of the Sharks is formed by a single coracoid
cartilage bent from the dorsal region downwards and forwards. In some
genera (_Scyllium_, _Squatina_) a small separate scapular cartilage
is attached to the dorsal extremities of the coracoid; but in none of
the Elasmobranchs is the scapular arch suspended from the skull or
vertebral column; it is merely sunk, and fixed in the substance of
the muscles. Behind, at the point of its greatest curvature, three
carpal cartilages are joined to the coracoid, which Gegenbaur has
distinguished as _propterygium_, _mesopterygium_, and _metapterygium_,
the former occupying the front, the latter the hind margin of the fin.
Several more or less regular transverse series of styliform cartilages
follow. They represent the phalanges, to which the horny filaments
which are imbedded in the skin of the fin are attached.

In the Rays, with the exception of _Torpedo_, the scapular arch is
intimately connected with the confluent anterior portion of the
vertebral column. The anterior and posterior carpal cartilages are
followed by a series of similar pieces, which extend like an arch
forwards to the rostral portion of the skull, and backwards to the
pubic region. Extremely numerous phalangeal elements, longest in the
middle, are supported by the carpals, and form the skeleton of the
lateral expansion of the so-called _disk_ of the Ray’s body, which
thus, in fact, is nothing but the enormously enlarged pectoral fin.

The _pubic_ is represented by a single median transverse cartilage,
with which a tarsal cartilage articulates. The latter supports the
fin-rays. To the end of this cartilage is also attached, in the male
Chondropterygians, a peculiar accessory generative organ or clasper.

The _Holocephali_ differ from the other Chondropterygians in several
important points of the structure of their skeleton, and approach
unmistakably certain Ganoids. That their spinal column is persistently
notochordal has been mentioned already. Their palatal apparatus, with
the suspensorium, coalesces with the skull, the mandible articulating
with a short apophysis of the cranial cartilage. The mandible is
simple, without anterior symphysis. The spine with which the dorsal
fin is armed articulates with a neural apophysis, and is not immovably
attached to it, as in the Sharks. The pubic consists of two lateral
halves, with a short, rounded, tarsal cartilage.

The skeleton of the _Ganoid_ Fishes offers extreme variations with
regard to the degree in which ossifications replace the primordial
cartilage. Whilst some exhibit scarcely any advance beyond the
Plagiostomes with persistent cartilage, others approach, as regards the
development and specialisation of the several parts of their osseous
framework, the Teleosteans so closely that their Ganoid nature can
be demonstrated by, or inferred from, other considerations only. All
Ganoids possess a separate gill-cover.[7]

The diversity in the development of the Ganoid skeleton is well
exemplified by the few representatives of the order in the existing
Fish-fauna. Lowest in the scale (in this respect) are those with a
persistent notochord, and an _autostylic_ skull, that is, a skull
without separate suspensorium--the fishes constituting the suborder
_Dipnoi_, of which the existing representatives are _Lepidosiren_,
_Protopterus_, and _Ceratodus_, and the extinct (as far as demonstrated
at present) _Dipterus_, _Chirodus_ (and _Phaneropleuron_?). In these
fishes the notochord is persistent, passing uninterruptedly into the
cartilaginous base of the skull. Only now and then a distinct vertical
segmentation occurs in the caudal portion of the column, but it does
not extend to the notochord itself, but indicates only the limits
between the superadded apophyseal elements, each neural being confluent
with the opposite hæmal. Some _Dipnoi_ are diphy-, others heterocercal.

Neural and hæmal elements and ribs are well developed. In _Ceratodus_
each neurapophysis consists of a basal cartilaginous portion, forming
an arch over the myelon, and of a superadded second portion. The
latter is separated from the former by a distinct line of demarcation,
and its two branches are more styliform, cartilaginous at the ends
and in the centre, but with an osseous sheath, and coalesced at the
top, forming a gable over an elastic fibrous band which runs along
and parallel to the longitudinal axis of the column (_Ligamentum
longitudinale superius_). To the top of this gable is joined a single
long cylindrical neural spine. From the eleventh apophyseal segment a
distinct interneural spine, of the same structure as the neural, begins
to be developed, and farther on a second interneural is superadded.
Towards the extremity of the column these various pieces are gradually
reduced in size and number, finally only a low cartilaginous band (the
rudiments of the neurapophysis) remaining. The _hæmapophyses_ are in
form, size, and structure, very similar to the neurapophyses; and all
these long bones, including the ribs, have that in common, that they
consist of a solid rod of cartilage enclosed in a bony sheath, which,
after the disappearance or decomposition of the cartilage, appears as
a hollow tube. Such bones are extremely common throughout the order of
Ganoids, and their remains have led to the designation of a family as
_Cœlacanthi_ (κοιλος, hollow; and ἀκανθος, spine).

The primordial _cranium_ of the _Dipnoi_ is cartilaginous, but with
more or less extensive ossifications in its occipital, basal, or
lateral portions, and with large tegumentary bones, the arrangement
of which varies in the different genera. There is no separate
suspensorium for the lower jaw. A strong process descends from the
cranial cartilage, and offers by means of a double condyle (Fig. 35
_s_) attachment to corresponding articulary surfaces of the lower
jaw. Maxillary and intermaxillary elements are not developed, but,
perhaps, represented in _Ceratodus_ by some inconstant rudimentary
labial cartilages situated behind the posterior nasal opening.
Facial cartilages and an infraorbital ring are developed at least
in _Ceratodus_. The presence of a pair of small teeth in front
indicates the vomerine portion (_v_) which remains cartilage, whilst
the posterior pair of teeth are implanted in a pterygo-palatine
ossification (_l_), which sometimes is paired, sometimes continuous.
The base of the skull is constantly covered by a large basal
ossification (_o_).

  [Illustration: Fig. 35.--Palatal view of Skull of Ceratodus.]

The _hyoid_ is well developed, sometimes reduced to a pair of
ceratohyals, sometimes with a basihyal and glossyhyal. The skeleton of
the _branchial apparatus_ approaches the Teleosteous type, less so in
_Lepidosiren_ than in _Ceratodus_, in which five branchial arches are
developed, but with the lateral and mesial pieces reduced in number.

A large operculum, and a smaller sub- or interoperculum are present.

The _scapular_ arch consists of a single median transverse cartilage,
and a pair of lateral cartilages which bear the articular condyle for
the pectoral limb. The latter cartilages form the base of a large
membrane-bone, and the whole arch is suspended from the skull by means
of an osseous supraclavicle.

The fore-limb of the _Dipnoi_ (Fig. 36) differs externally greatly
from the pectoral fin of other Ganoid fishes. It is covered with
small scales along the middle, from the root to its extremity, and
surrounded by a rayed fringe similar to the vertical fin. A muscle
split into numerous fascicles extends all the length of the fin, which
is flexible in every part and in every direction. The cartilaginous
framework supporting it is joined to the scapular arch by an oblong
cartilage, followed by a broad basal cartilage (_a_), generally single,
sometimes showing traces of a triple division. Along the middle of the
fin runs a jointed axis (_b_), the joints gradually becoming smaller
and thinner towards the extremity; each joint bears on each side a
three, two, or one-jointed branch (_c, d_). This _axial_ arrangement of
the pectoral skeleton, which evidently represents one of its first and
lowest conditions, has been termed _Archipterygium_ by Gegenbaur. It is
found in _Ceratodus_ and other genera, but in _Lepidosiren_ the jointed
axis only has been preserved, with the addition of rudimentary rays in
_Protopterus_.

  [Illustration: Fig. 36.--Fore-limb of Ceratodus.]

The _pubic_ consists of a single flattened subquadrangular cartilage,
produced into a long single anterior process. Posteriorly it terminates
on each side in a condyle, to which the basal cartilage of the ventral
paddle is joined. The endoskeleton of the paddle is almost identical
with that of the pectoral.

The Ganoid fishes with persistent notochord, but with a _hyostylic_
skull (that is, a skull with a separate suspensorium) consist of the
suborder _Chondrostei_, of which the existing representatives are the
Sturgeons (_Acipenser_, _Scaphirhynchus_, _Polyodon_), and the extinct
the _Chondrosteidæ_, _Palæoniscidæ_, and (according to Traquair)
_Platysomidæ_.

Their spinal column does not differ essentially from that of the
Dipnoi. Segmentation is represented only as far as the neural and
hæmal elements are concerned. All are eminently heterocercal. Ribs are
present in most, but replaced by ligaments in _Polyodon_.

  [Illustration: Fig. 37.--Skull of Polyodon (after Traquair).

    _n_, Nasal cavity; _sq_, squamosal; _mh_, hyomandibular;
    _sy_, symplectic; _pa_, palato-pterygoid; _m_, Meckelian
    cartilage; _mx_, maxillary; _d_, dentary; _h_, hyoid; _op_,
    opercle; _br_, branchiostegal; _s.cl_, supra-clavicular;
    _p.cl_, post-clavicular; _cl_, clavicle; _i.cl_,
    infra-clavicular.]

The primordial cranium of the Sturgeons consists of persistent
cartilage without ossifications in its substance, but superficial bones
are still more developed and specialised than in the Dipnoi; so it is,
at least, in the true Sturgeons, but less so in _Polyodon_ (Fig. 37).
The upper and lateral parts of the skull are covered by well-developed
_membrane bones_, which, from this suborder, upwards in the series,
will be found to exist throughout the remaining forms of fishes. They
are bones, the origin of which is not in cartilage but in membranous
connective tissue. The lower surface of the skull is covered by an
extremely large basal bone, which extends from the vomerine region
on to the anterior part of the spinal column. The nasal excavation
in the skull is rather lateral than inferior. The ethmoidal region
is generally much produced, forming the base of the long projecting
snout. The suspensorium is movably attached to the side of the skull,
and consists of two pieces, a hyomandibular and a symplectic, which
now appears for the first time as a separate piece, and to which the
hyoid is attached. The palato-maxillary apparatus is more complex
than in the Sharks and Dipnoi; a palato-pterygoid consists of two
mesially-connected rami in _Polyodon_, and of a complex cartilaginous
disk in _Acipenser_, being articulated in both to the Meckelian
cartilage. In addition, the Sturgeons possess one or two pairs of
osseous rods, which, in _Polyodon_ at least, represent the maxillary,
and therefore must be the representatives of the labial cartilages
of the Sharks. The Meckelian cartilage is more or less covered by
tegumentary bones.

In the gill-cover, besides the operculum, a sub- and interoperculum may
be distinguished in _Acipenser._

The hyoid consists of three pieces, of which the posterior bears a
broad branchiostegal in _Polyodon._

In the scapulary arch the primordial cartilaginous elements scarcely
differ from those of the _Dipnoi._ The membrane-bones are much
expanded, and offer a continuous series suspended from the skull. Their
division in the median ventral line is complete.

  [Illustration: Fig. 38.--Fore-limb of Acipenser.]

The pectoral is supported by a cartilaginous framework (Fig. 38)
similar to that of _Ceratodus_, but much more shortened and reduced in
its periphery, the branches being absent altogether on one side of the
axis. This modification of the fin is analogous to the heterocercal
condition of the end of the spinous column. To the inner corner of a
basal cartilage (_a_) a short axis (_b_) is joined, which on its outer
side bears a few branches (_d_) only, the remaining branches (_c_)
being fixed to the basal cartilage. The dermal fin-rays are opposed to
the extremities of the branches, as in the _Dipnoi_.

The _pubic_ consists of a paired cartilage, to which tarsal pieces
supporting the fin-rays are attached.

The other living Ganoid fishes have the spinous column entirely or
nearly entirely ossified, and have been comprised under the common name
_Holostei_. However, they form three very distinct types; several
attempts have been made to coordinate with them the fossil forms, but
this task is beset with extreme difficulties, and its solution hitherto
has not proved to be satisfactory.

The _Polypteroidei_ have their spinous column formed by distinct
osseous _amphicœlous_ vertebræ, that is, vertebræ with concave anterior
and posterior surfaces. It is nearly diphycercal; a slight degree of
heterocercy obtains, inasmuch as the last vertebra is succeeded by a
very thin cartilaginous filament which penetrates between the halves
of one of the middle rays of the terminal fin. The rays above this
cartilaginous filament are articulated to interneurals, those below
lack interhæmals, and are attached either to the hæmals or vertebral
centres. The neural arches, though ossified, do not coalesce with
the centrum, and form one canal only, for the myelon. There are
no intermediate elements between the neural spines. Interneurals
developed, but simple, articulating with the dermoneurals. The
abdominal vertebræ have parapophyses developed with epipleural
spines. Only the caudal vertebræ have hæmal spines, which, like the
interhæmals, agree in every essential respect with the opposite
neurals. _Ribs_ are inserted, not on the parapophyses, but on the
centre, immediately below the parapophyses.

The _skull_ of _Polypterus_ (Fig. 39) shows a great advance towards
the Teleosteous type, the number of separable bones being greatly
increased. They are arranged much in the same fashion as in Teleostei.
But a great portion of the primordial cranium remains cartilaginous.
The membrane-bones which cover the upper and lower surfaces of the
brain-case are so much developed as to cause the underlying cartilage
to disappear, so that a large vacuity or fontanelle exists in the
substance of the upper as well as lower cartilaginous wall. Of
ossifications belonging to the primordial skull must be noticed the
single occipital with a mastoid on each side. They are separated by
persistent cartilage from the sphenoids and postfrontals; the former,
which are the largest ossification of the primordial cranium, enclose
the anterior half of the brain cavity. Finally, the nasal portion
contains a median ethmoid and a pair of præfrontal bones.

  [Illustration: Fig. 39.--Skull of Polypterus. (After Traquair.)

   Fig. I. Upper aspect of the Primordial Cranium, with the
   membrane-bones removed. Fig. II. Lower aspect of the same. Fig.
   III. Side view, with the membrane-bones. Fig. IV. Lower aspect
   of the Skull, part of the bones being removed on one side. The
   parts shaded with oblique lines are cartilage of the primordial
   skull.

   _An_, Angular; _ao_, ante-orbital; _Ar_,
   articulary; _B_, basal; _D_, dentary; _E_,
   ethmoid; _F_, frontal; _Ma_, mastoid; _Mp_,
   metapterygoid; _Mx_, maxillary; _N_, nasal; _O_,
   operculum; _Oc_, occipital; _Pa_, parietal; _Pl_,
   palatine; _Pmx_, præmaxillary; _po_, post-orbital;
   _Prf_, prefrontal; _Pt_, post-temporals; _Ptf_,
   postfrontal; _Ptr_, pterygoid; _Q_, quadrate;
   _S_, suspensorium; _So_, sub-operculum; _Sp_,
   sphenoid; _Spl_, splenial; _St_, supratemporals;
   _T_, tympanic lamina; _Tu_, turbinal; _v_, vomer;
   _x x_, small ossicles; _x’ x’_, spiraculars.]


Only a very small portion of the bones described are visible
externally, nearly the whole of the primordial cranium being covered
by the membrane-bones. Of these are seen on the upper surface a pair
of parietals, frontals, “nasals,” and turbinals; on the lower surface
a large cross-shaped basal, anteriorly bordered on each side by a
pterygoid, parallel to a palatine which forms a suture with the double
vomer. The suspensorium has in front a metapterygoid and quadrate bone,
and an operculum and sub-operculum are attached to it behind.

Præmaxillaries and maxillaries are now fully developed, but immovably
attached to the skull. The lower jaw is ossified, and consists of an
articulary, angular, dentary, and splenial. Of labial cartilages a
rudiment at the angle of the mouth has remained persistent.

The side of the skull, in front of the operculum, is covered by a large
irregularly-shaped bone (_T_) (corresponding to the “tympanic lamina”
of _Ceratodus_, Fig. 35, _q_), held by some to be the præoperculum;
along its upper circumference lies a series of small ossicles, of which
two may be distinguished as spiraculars, as they form a valve for the
protection of the spiracular orifice of these fishes. An infraorbital
ring is represented by a præ- and post-orbital only.

Each _hyoid_ consists of three pieces, none of which bear
branchiostegals, the single median piece being osseous in front and
cartilaginous behind. Four branchial arches are developed, the foremost
consisting of three, the second and third of two, and the last of a
single piece. There is no lower pharyngeal. Between the rami of the
lower jaw the throat is protected by a pair of large osseous laminæ
(_gular plates_), which have been considered to represent the urohyal
of osseous fishes.

The scapulary arch is almost entirely formed by the well-developed
membrane-bones, which in the ventral line are suturally united.
The pectoral fin is supported by three bones, pro-, meso-, and
metapterygium, of which the dilated middle one alone bears rays, and is
excluded from the articulation with the shoulder-girdle.

The pubic consists of paired bone, to which tarsal bones supporting the
fin-rays are attached.

In the _Lepidosteoidei_ the vertebræ are completely ossified, and
_opisthocœlous_, having a convexity in front and a concavity behind,
as in some Amphibians. Though the end of the body externally appears
nearly diphycercal, the termination of the vertebral column is,
in fact, distinctly heterocercal (Fig. 40). Its extremity remains
cartilaginous, is turned upwards, and lies immediately below the scutes
which cover the upper margin of the caudal fin. It is preceded by a
few rudimentary vertebræ which gradually pass into the fully developed
normal vertebræ. The caudal fin is suspended from hæmapophyses only,
and does not extend to the neural side of the vertebral column. The
neural arches coalesce with the centrum; interneurals simple. The
abdominal vertebræ have parapophyses, to which the ribs are attached.
Only the caudal vertebræ have hæmal spines.

  [Illustration: Fig. 40.--Heterocercal Tail of Lepidosteus.

    _n_, Vertebral column; _h_, hæmal spines; _dn_, fulcra; _dh_,
    lower fulcra.]

In the skull of _Lepidosteus_ the cartilage of the endocranium is
still more replaced by ossifications than in _Polypterus_; those
ossifications, moreover, being represented by a greater number of
discrete bones; especially the membrane-bones are greatly multiplied:
the occipital, for instance, consists of three pieces; the vomer is
double as in _Polypterus_; the maxillary consists of a series of
pieces firmly united by suture. The symplectic reaches the lower jaw,
so that the articulary is provided with a double joint, viz. for the
symplectic and quadrate; the component parts of the lower jaw are as
numerous as in reptiles, a dentary, splenial, articulary, angular,
supra-angular, and coronary being distinct. The sides of the head
are covered with numerous bones, and a præoperculum is developed in
front of the gill-cover which, again, consists of an operculum and
sub-operculum.

Each hyoid consists of three pieces, of which the middle is the
longest, the upper bearing the largest of the three branchiostegals
which _Lepidosteus_ possesses; a long and large glossohyal is
intercalated between the lower ends of the hyoids. There are five
branchial arches, the hindmost of which is modified into a lower
pharyngeal; upper pharyngeals are likewise present as in the majority
of Teleosteous fishes. No gular plate.

Of the scapulary arch the two halves are separated by a suture in the
median line; the membrane-bones are well developed, only a remnant of
the primordial cartilage remaining; the supraclavicle is very similar
to that of Teleosteous fishes, less so the post-temporal. The base to
which the limb is attached is a single osseous plate, supporting on its
posterior margin semi-ossified rods in small number, which bear the
pectoral rays.

The pubic consists of paired bone, the anterior ends of which overlap
each other, the extremity of the right pubis being dorsad to that of
the left. The elements representing a tarsus are quite rudimentary and
reduced in number (two or three).

The vertebral column of the _Amioidei_ shows unmistakable characters
of the Palæichthyic type. The arrangement of its component parts is
extremely simple. The centra of the amphicœlous vertebræ are well
ossified, but the neural and hæmal arches do not coalesce with the
centra, from which they are separated by a thin layer of cartilage.
Singularly, not every vertebra has apophyses: in the caudal portion of
_Amia_ the vertebræ are alternately provided with them and lack them.
The heterocercal condition of the spinous column is well marked: as in
the other Holostei the hindmost vertebræ are turned upwards, become
smaller and smaller in size, and lose their neural arches, the hæmals
remaining developed to the end. Finally, the column terminates in a
thin cartilaginous band, which is received between the lateral halves
of the fifth or sixth upper caudal ray. Interneurals and interhæmals
simple. Only the abdominal vertebræ have parapophyses, with which the
ribs are articulated.

The configuration of the skull, and the development and arrangement
of its component parts, approaches so much the Teleosteous type that,
perhaps, there are greater differences in skulls of truly Teleosteous
fishes than between the skulls of _Amia_ and many _Physostomi_.
Externally the cranium is entirely ossified; and the remains of the
cartilaginous primordial cranium (which, however, has no vacuity in its
roof) can only be seen in a section, and are of much less extent than
in many Physostomous fishes. The immovable intermaxillary, the double
vomer, the plurality of ossifications representing the articulary,
the double articulary cavity of the mandible for junction with the
quadrate and symplectic bones, remind us still of similar conditions
in the skull of _Lepidosteus_, but the mobility and formation of the
maxillary, the arrangement of the gill-covers, the development of the
opercles, the suspensorium, the palate, the insertion of a number of
branchiostegals on the long middle hyoid piece, the composition of the
branchial framework (with upper and lower pharyngeals), are as in the
Teleosteous type. A gular plate replaces the urohyal.

The scapular arch is composed entirely of the membrane-bones found in
the _Teleostei_, and the two sides are loosely united by ligament.
The base to which the limb is attached is cartilaginous; short
semi-ossified rods are arranged along its hinder margin and bear the
pectoral rays.

The skeleton of the hind-limb agrees entirely with that of
_Lepidosteus_.

   [T. W. Bridge, The Cranial Osteology of _Amia calva_; in
   Journ. Anat. and Physiol. vol. xi.]

In the _Teleosteous_ fishes the spinous column consists of completely
ossified amphicœlous vertebræ; its termination is _homocercal_--that
is, the caudal fin appears to be more or less symmetrical, the last
vertebra occupying a central position in the base of the fin, and being
coalesced with a flat osseous lamella, the _hypural_ (Fig. 23, 70), on
the hind margin of which the fin-rays are fixed. The hypural is but a
union of modified hæmapophyses which are directed backwards, and the
actual termination of the notochord is bent upwards, and lies along the
upper edge of the hypural, hidden below the last rudimentary neural
elements. In some Teleosteans, as the _Salmonidæ_, the last vertebræ
are conspicuously bent upwards: in fact, strictly speaking, this
homocercal condition is but one of the various degrees of heterocercy,
different from that of many Ganoids in this respect only, that the
caudal fin itself has assumed a higher degree of symmetry.

The neural and hæmal arches generally coalesce with the centrum, but
there are many exceptions, inasmuch as some portion of the arches of a
species, or all of them, show the original division.

The vertebræ are generally united with one another by zygapophyses, and
frequently similar additional articulations exist at the lower parts
of the centra. Parapophyses and ribs are very general, but the latter
are inserted on the centra and the base of the processes, and never on
their extremities. The point of insertion of the rib, more especially
on the anterior vertebræ, may be still higher--viz. at the base of the
neural arch, as in _Cotylis_ and allied genera, and even on the top of
the neurapophysis, as in _Batrachus_.

There is a great amount of variation as regards the degree in which
the primordial cranium persists; it is always more or less replaced by
bone; frequently it disappears entirely, but in some fishes, like the
_Salmonidæ_ or _Esocidæ_, the cartilage persists to the same or even
to a greater extent than in the Ganoidei holostei. Added to the bones
preformed in cartilage are a great number of _membrane-bones_. The
different kinds of these membrane-bones occur with greater or less
constancy throughout this sub-class; they often coalesce with, and are
no more separable from, the neighbouring or underlying cartilage-bones.
All these bones have been topographically enumerated in Chapter IV.

Many attempts have been made to classify the bones of the Teleosteous
skull, according to their supposed relation to each other, or with
the view to demonstrate the unity of plan on which the skull has been
built; but in all either the one or the other of the following two
principles has been followed:--

A. The “vertebral doctrine” starts from the undeniable fact that the
skull is originally composed of several segments, each of which is
merely the modification of a vertebra. The component parts of such a
cranial segment are considered to be homologous to those of a vertebra.
Three, four, or five cranial vertebræ have been distinguished, all
the various bones of the fully-developed and ossified skull being
referred, without distinction as to their origin, to one or the other
of those vertebral segments. The idea of the typical unity of the
osseous framework of Vertebrates has been worked out with the greatest
originality and knowledge of detail, by _Owen_, who demonstrates that
the fish-skull is composed of _four_ vertebræ.

The bones of the fish-skull are, according to him, primarily
divisible into those of the _neuroskeleton_, _splanchnoskeleton_, and
_dermoskeleton_.

The bones of the _neuro_- or proper _endoskeleton_ are arranged in
a series of four horizontally succeeding segments: the occipital,
parietal, frontal, and nasal vertebræ; each segment consisting of an
upper (neural) and a lower (hæmal) arch, with a common centre, and with
diverging appendages.

The _neural_ arches of the four vertebræ, in their succession from the
occiput towards the snout, are:--

1. _Epencephalic arch_, composed of the occipitals.

2. _Mesencephalic arch_, composed of basisphenoid, alisphenoid,
parietal, and mastoid.

3. _Prosencephalic arch_, composed of presphenoid, orbito-sphenoid,
frontal, and postfrontal.

4. _Rhinencephalic arch_, composed of vomer, prefrontal, and nasal.

The _hæmal_ arches in the same order of succession are:--

1. _Scapular_ or _scapulo-coracoid_ arch, composed of suprascapula,
scapula, and coracoid; its appendage consists of the ulna, radius and
carpal.

2. _Hyoid_ or _stylo-hyoid_ arch, composed of stylohyal, epihyal,
ceratohyal, basihyal, glossohyal, and urohyal; its appendage is the
branchiostegals.

3. _Mandibular_ or _tympano-mandibular_ arch, composed of epi-, meso-,
pre-, and hypo-tympanic, and the bones of the lower jaw; its appendage
consists of the præoperculum and the other opercles.

4. _Maxillary_ or _palato-maxillary_ arch, composed of palatine,
maxillary, and premaxillary; its appendage consists of the pterygoid
and entopterygoid.

Parts of the _splanchnoskeleton_ are held to be the ear-capsule
or petrosal and the otolite, the eye-capsule or sclerotic, the
nose-capsule or “ethmoid” and turbinal; the branchial arches.

The bones of the _dermoskeleton_ are the supratemporals, supraorbitals,
suborbitals, and labials.

B. In the second method of classifying the bones of the skull
prominence is given to the facts of their different origin as
ascertained by a study of their development. The parts developed from
the primordial skull, or the cartilaginous case protecting the nervous
centre are distinguished from those which enclose and support the
commencement of the alimentary canal and the respiratory apparatus, and
which, consisting of several arches, are comprised under the common
name of _visceral skeleton of the skull_. Further, a distinction is
made between the bones preformed in cartilage and those originating in
tegumentary or membranous tissue. It is admitted that the primordial
cranium is a coalition of several segments, the number of which is
determined by that of the visceral arches, these representing the hæmal
arches of the vertebral column; but the membrane-bones are excluded
from a consideration of the vertebral division of the primordial skull,
as elements originally independent of it, although these additions have
entered into special relations to the cartilage-bones.

With these views the bones of the Teleosteous skull are classified
thus:--

1. _Cartilage-bones of the primordial skull_.--The _basi-occipital_
(5 in Figs. 23–26) has retained the form of a vertebral centrum; it
is generally concave behind, the concavity containing remains of the
notochord; rarely a rounded articulary head of the first vertebra fits
into it, as in _Symbranchus_, and still more rarely it is provided
with such an articulary head (_Fistularia_); frequently it shows two
excavations on its inner surface for the reception of the _saccus
vestibuli_. The _exoccipitals_ (10) are situated on the side of the
basi-occipital, and contribute the greater portion of the periphery of
the foramen magnum; frequently they articulate with the first vertebra,
or meet in the upper median line, so as to exclude the supraoccipital
from the foramen magnum. The _supraoccipital_ (8) is intercalated
between the exoccipitals, and forms a most prominent part by the median
crest, which sometimes extends far forwards on the upper side of the
skull, and offers attachment to the dorsal portion of the large lateral
muscle of the trunk. When the interior portions of this bone remain
cartilaginous, some part of the semicircular canals may be lodged in it.

The region of the skull which succeeds the bones described encloses at
least the greater portion of the labyrinth, and its component parts
have been named with reference to it by some anatomists.[8] The
_alisphenoids_ (11) (_Prooticum_) form sutures posteriorly with the
basi- and exoccipitals, and meet each other in the median line at the
bottom of the cerebral cavity; they contribute to the formation of a
hollow in which the hypophysis cerebri and the saccus vasculosus are
received; in conjunction with the exoccipital it forms another hollow
for the reception of the vestibulum; generally it is perforated by the
Trigeminal and Facial nerves. The _paroccipitals_ (9) (_Epioticum_)
lodge a portion of the posterior vertical semicircular canal, and form
a projection of the skull on each side of the occipital crest, to which
a terminal branch of the scapular arch is attached. The _Mastoid_ (12
+ 13) (_Opisthoticum_) occupies the postero-external projection of
the head; it encloses a part of the external semicircular canal; is
generally coalesced with a membrane-bone, the superficial _squamosal_,
which emits a process for the suspension of the scapular arch, and is
frequently, as in the Perch, divided into two separate bones.

The anterior portion of the skull varies greatly as regards form, which
is chiefly dependent on the extent of the cerebral cavity; if the
latter is advanced far forwards, the lateral walls of the primordial
cranium are protected by more developed ossifications than if the
cerebral cavity is shortened by the presence of a wide and deep orbit.
In the latter case parts which normally form the side of the skull are
situated in front of the brain-case, between it and the orbit, and
generally reduced in extent, often replaced by membranes; especially
the interorbital septum may be reduced to membrane. The most constant
ossifications of this part of the skull are the _orbitosphenoids_
(14), which join the upper anterior margin of the alisphenoids. They
vary much with regard to their development--they are small in Gadoids;
larger in the Perch, Pike, Salmonoids, Macrodon, and the Clupeoids;
and very large in Cyprinoids and Siluroids, in which they contribute
to the formation of the side of the brain-case. The single Y-shaped
_Sphenoideum anterius_ (15) is as frequently absent as present; it
forms the anterior margin of the fossa for the hypophysis. Finally, the
_postfrontal_ (4) belongs also to this group of cartilage-bones.

The centre of the foremost part of the skull is occupied by the
_ethmoid_ (3), which shows great variations as regards its extent
and the degree of ossification; it may extend backwards into the
interorbital septum, and reach the orbitosphenoids, or may be confined
to the extremity of the skull; it may remain entirely cartilaginous,
or ossify into a lamina which separates the two orbits and encloses
an anterior prolongation of the brain-case, along which the olfactory
nerves pass: modifications occurring again in higher vertebrates. A
paired ossification attached to the fore-part of the ethmoid is the
_pre-frontals_ (2), which form the base of the nasal fossa.

2. _Membrane-bones attached to the primordial skull_.--To this group
belong the _parietals_ (7) and _frontals_ (1). The _squamosal_ (12) has
been mentioned above in connection with the mastoid. The _supraorbital_
is always small, and frequently absent. The lower surface of the skull
is protected by the _basisphenoid_ (parasphenoid) (6) and the _vomer_
(16), both of which, especially the latter, may be armed with teeth.[9]

3. _Cartilage bones of the alimentary portion of the visceral skeleton
of the skull_.--The suspensorium consists of three cartilage-bones,
and affords a base for the opercular apparatus as well as a point of
attachment to the hyoid, whilst in front it is connected with the
palato-pterygo-palatine arch. They are the _hyomandibular_ (23),
_symplectic_ (31), and _quadrate_ (26), connected by means of the
_metapterygoid_ (27) with the _ecto-_ (24) and _ento-pterygoid_ (25),
the foremost bone of the arch being the _palatine_ (22). All these
bones have been sufficiently described above (p. 55), and it remains
only to be mentioned that the bones of the palatine arch are but rarely
absent, as for instance in _Murænophis_; and that the symplectic
does not extend to the articulary of the mandible, as in _Amia_
and _Lepidosteus_, though its suspensory relation to the Meckelian
cartilage is still indicated by a ligament which connects the two
pieces. Of the mandibulary bones the _articulary_ (35) is distinctly
part of Meckel’s cartilage. Frequently another portion of cartilage
below the articulary remains persistent, or is replaced by a separate
membrane-bone, the angular.

4. _Membrane-bones of the alimentary portion of the visceral skeleton
of the skull_.--The suspensorium has one tegumentary bone attached
to it, viz. the _præoperculum_ (30); it is but rarely absent, for
instance in _Murænophis_. The _premaxillary_ (17) and _maxillary_ (18)
of the Teleostei appear to be also membrane-bones, although they are
clearly analogous to the upper labial cartilages of the Sharks. The
premaxillaries sometimes coalesce into a single piece (as in _Diodon_,
_Mormyrus_), or they are firmly united with the maxillaries (as in all
_Gymnodonts_, _Serrasalmo_, etc.) The relative position and connection
of these two bones differs much, and is a valuable character in the
discrimination of the various families. In some, the front margin of
the jaw is formed by the premaxillary only, the two bones having a
parallel position, as it has been described in the Perch (p. 53); in
others, the premaxillary is shortened, allowing the maxillary to enter,
and to complete, the margin of the upper jaw; and finally, in many no
part of the maxillary is situated behind the premaxillary, but the
entire bone is attached to the end of the premaxillary, forming its
continuation. In the last case the maxillary may be quite abortive.
The mobility of the upper jaw is greatest in those fishes in which the
premaxillary alone forms its margin. The form of the premaxillary is
subject to great variation: the beak of _Belone_, _Xiphias_ is formed
by the prolonged and coalesced premaxillaries. The maxillary consists
sometimes of one piece, sometimes of two or three. The principal
membrane-bone of the mandible is the _dentary_ (34), to which is added
the _angular_ (36) and rarely a smaller one, the _splenial_ or os
_operculare_, which is situated at the inside of the articulary.

5. _Cartilage-bones of the respiratory portion of the visceral skeleton
of the skull._--With few exceptions all the ossifications of the hyoid
and branchial arches, as described above (p. 58), belong to this group.

6. _Membrane-bones of the respiratory portion of the visceral skeleton
of the skull._--They are the following: the opercular pieces, viz.
_operculum_ (28), _sub-operculum_ (32), and _interoperculum_ (33). The
last of these is the least constant; it may be entirely absent, and
represented by a ligament extending from the mandible to the hyoid.
The _urohyal_ (42) which separates the musculi sternohyoidei, and
serves for an increased surface of their insertion; and finally the
_branchiostegals_ (43), which vary greatly in number, but are always
fixed to the cerato- and epi-hyals.

7. _Dermal bones of the skull._--To this category are referred some
bones which are ossifications of, and belong to, the cutis. They are
the _turbinals_ (20), the _suborbitals_ (19), and the _supratemporals_.
They vary much with regard to the degree in which they are developed,
and are rarely entirely absent. Nearly always they are wholly or partly
transformed into tubes or hollows, in which the muciferous canals with
their numerous nerves are lodged. Those in the temporal and scapulary
regions are not always developed; on the other hand, the series of
those ossicles may be continued on to the trunk, accompanying the
lateral line. In many fishes those of the infraorbital ring are much
dilated, protecting the entire space between the orbit and the rim of
the præoperculum; in others, especially those which have the angle of
the præoperculum armed with a powerful spine, the infraorbital ring
emits a process towards the spine, which thus serves as a stay or
support of this weapon (_Scorpænidæ_, _Cottidæ_).

The _pectoral_ arch of the Teleosteous fishes exhibits but a remnant of
a primordial cartilage, which is replaced by two ossifications,[10] the
_coracoid_ (51) and _scapula_ (52); they offer posteriorly attachment
to two series of short rods, of which the proximal are nearly always
ossified, whilst the distal frequently remain small cartilaginous
nodules hidden in the base of the pectoral rays. The bones, by
which this portion is connected with the skull, are membrane-bones,
viz. the _clavicle_ (49), with the _postclavicle_ (49 + 50), the
_supraclavicle_ (47), and _post-temporal_ (46). The order of their
arrangement in the Perch has been described above (p. 59). However,
many Teleosteous fish lack pectoral fins, and in them the pectoral arch
is frequently more or less reduced or rudimentary, as in many species
of _Murænidæ_. In others the membrane-bones are exceedingly strong,
contributing to the outer protective armour of the fish, and then the
clavicles are generally suturally connected in the median line. The
postclavicula and the supraclavicula may be absent. Only exceptionally
the shoulder-girdle is not suspended from the skull, but from the
anterior portion of the spinous column (_Symbranchidæ_, _Murænidæ_,
_Notacanthidæ_). The number of basal elements of each of the two series
never exceeds five, but may be less; and the distal series is absent in
Siluroids.

The _pubic_ bones of the Teleosteous fishes undergo many modifications
of form in the various families, but they are essentially of the same
simple type as in the Perch.




                              CHAPTER V.

                               MYOLOGY.


In the lowest vertebrate, _Branchiostoma_, the whole of the
_muscular_ mass is arranged in a longitudinal band running along
each side of the body; it is vertically divided into a number of flakes
or segments (_myocommas_) by aponeurotic septa, which serve as the
surfaces of insertion to the muscular fibres. But this muscular band
has no connection with the notochord except in its foremost portion,
where some relation has been formed to the visceral skeleton. A very
thin muscular layer covers the abdomen.

Also in the _Cyclostomes_ the greatest portion of the muscular
system is without direct relation to the skeleton, and, again, it is
only on the skull and visceral skeleton where distinct muscles have
been differentiated for special functions.

To the development of the skeleton in the more highly organised fishes
corresponds a similar development of the muscles; and the maxillary
and branchial apparatus, the pectoral and ventral fins, the vertical
fins, and especially the caudal, possess a separate system of muscles.
But the most noteworthy is the muscle covering the sides of the trunk
and tail (already noticed in _Branchiostoma_), which Cuvier described
as the “great lateral muscle,” and which, in the higher fishes, is a
compound of many smaller segments, corresponding in number with the
vertebræ. Each lateral muscle is divided by a median longitudinal
groove into a dorsal and ventral half; the depression in its middle
is filled by an embryonal muscular substance which contains a large
quantity of fat and blood-vessels, and therefore differs from ordinary
muscle by its softer consistency, and by its colour which is reddish
or grayish. Superficially the lateral muscle appears crossed by a
number of white parallel tendinous zig-zag stripes, forming generally
three angles, of which the upper and lower point backwards, the middle
one forwards. These are the outer edges of the aponeurotic septa
between the myocommas. Each septum is attached to the middle and the
apophyses of a vertebra, and, in the abdominal region, to its rib;
frequently the septa receive additional support by the existence of
epipleural spines. The fibres of each myocomma run straight and nearly
horizontally from one septum to the next; they are grouped so as to
form semiconical masses, of which the upper and lower have their apices
turned backwards, whilst the middle cone, formed by the contiguous
parts of the preceding, has its apex directed forward; this fits into
the interspace between the antecedent upper and lower cones, the apices
of which reciprocally enter the depressions in the succeeding segment,
whereby all the segments are firmly locked together (_Owen_).

In connection with the muscles reference has to be made to the
_Electric organs_ with which certain fishes are provided, as it
is more than probable, not only from the examination of peculiar
muscular organs occurring in the Rays, _Mormyrus_, and _Gymnarchus_
(the function of which is still conjectural), but especially from the
researches into the development of the electric organ of _Torpedo_,
that the electric organs have been developed out of muscular substance.
The fishes possessing fully developed electric organs, with the power
of accumulating electric force and communicating it in the form of
shocks to other animals, are the electric Rays (_Torpedinidæ_), the
electric Sheath-fish of tropical Africa (_Malapterurus_), and the
electric Eel of tropical America (_Gymnotus_). The structure and
arrangement of the electric organ is very different in these fishes,
and will be subsequently described in the special account of the
several species.

The phenomena attending the exercise of this extraordinary faculty
also closely resemble muscular action. The time and strength of the
discharge are entirely under the control of the fish. The power is
exhausted after some time, and it needs repose and nourishment to
restore it. If the electric nerves are cut and divided from the brain
the cerebral action is interrupted, and no irritant to the body has any
effect to excite electric discharge; but if their ends be irritated
the discharge takes place, just as a muscle is excited to contraction
under similar circumstances. And, singularly enough, the application
of strychnine causes simultaneously a tetanic state of the muscles and
a rapid succession of involuntary electric discharges. The strength of
the discharges depends entirely on the size, health, and energy of the
fish: an observation entirely agreeing with that made on the efficacy
of snake-poison. Like this latter, the property of the electric force
serves two ends in the economy of the animals which are endowed with
it; it is essential and necessary to them for overpowering, stunning,
or killing the creatures on which they feed, whilst incidentally they
use it as the means of defending themselves from their enemies.




                              CHAPTER VI.

                              NEUROLOGY.


The most simple condition of the nervous central organ known in
Vertebrates is found in _Branchiostoma_. In this fish the spinal
chord tapers at both ends, an anterior cerebral swelling, or anything
approaching a brain, being absent. It is band-like along its middle
third, and groups of darker cells mark the origins of the fifty or
sixty pairs of nerves which accompany the intermuscular septa, and
divide into a dorsal and ventral branch, as in other fishes. The two
anterior pairs pass to the membranous parts above the mouth, and supply
with nerve filaments a ciliated depression near the extremity of the
fish, which is considered to be an olfactory organ, and two pigment
spots, the rudiments of eyes. An auditory organ is absent.

The _spinal chord_ of the _Cyclostomes_ is flattened in its
whole extent, band-like, and elastic; also in _Chimæra_ it is
elastic, but flattened in its posterior portion only. In all other
fishes it is cylindrical, non-ductile, and generally extending along
the whole length of the spinal canal. The Plectognaths offer a singular
exception in this respect that the spinal chord is much shortened, the
posterior portion of the canal being occupied by a long cauda equina;
this shortening of the spinal chord has become extreme in the Sun-fish
(_Orthagoriscus_), in which it has shrunk into a short and conical
appendage of the brain. Also in the Devil-fish (_Lophius_) a long
cauda equina partly conceals the chord which terminates on the level of
about the twelfth vertebra.

The _brain_ of fishes is relatively small; in the Burbot
(_Lota_) it has been estimated to be 1/720th part of the weight of
the entire fish, in the Pike the 1/1305th part, and in the large Sharks
it is relatively still smaller. It never fills the entire cavity of
the cranium; between the dura mater which adheres to the inner surface
of the cranial cavity, and the arachnoidea which envelops the brain, a
more or less considerable space remains, which is filled with a soft
gelatinous mass generally containing a large quantity of fat. It has
been observed that this space is much less in young specimens than in
adult, which proves that the brain of fishes does not grow in the same
proportion as the rest of the body; and, indeed, its size is nearly the
same in individuals of which one is double the bulk of the other.

  [Illustration: Fig. 41.--Brain of Perch.

  I. Upper aspect. II. Lower aspect.

    _a_, cerebellum; _b_, optic lobes; _c_, hemispheres; _e_,
    lobi inferiores; _f_, hypophysis; _g_, lobi posteriores; _i_,
    Olfactory lobes; _n_, _N._ opticus; _o_, _N._ olfactorius;
    _p_, _N._ oculo-motorius; _q_, _N._ trochlearis; _r_, _N._
    trigeminus; _s_, _N._ acusticus; _t_, _N._ vagus; _u_, _N._
    abducens; _v_, Fourth ventricle.]

The brain of _Osseous fishes_ (Fig. 41) viewed from above shows three
protuberances, respectively termed _prosencephalon_, _mesencephalon_,
and _metencephalon_, the two anterior of which are paired, the hindmost
being single. The foremost pair are the _hemispheres_, which are
solid in their interior, and provided with two swellings in front,
the _olfactory lobes_. The second pair are the _optic lobes_, which
generally are larger than the hemispheres, and succeeded by the third
single portion, _the cerebellum_. In the fresh state the hemispheres
are of a grayish colour, and often show some shallow depressions on
their surface; a narrow commissure of white colour connects them
with each other. The optic lobes possess a cavity (_ventriculus
lobioptici_), at the bottom of which some protuberances of variable
development represent the corpora quadrigemina of higher animals. On
the lower surface of the base of the optic lobes, behind the _crura
cerebri_, two swellings are observed, the _lobi inferiores_, which
slightly diverge in front for the passage of the _infundibulum_, from
which a generally large _hypophysis_ or _pituitary gland_ is suspended.
The relative size of the cerebellum varies greatly in the different
osseous fishes: in the Tunny and Silurus it is so large as nearly to
cover the optic lobes; sometimes distinct transverse grooves and a
median longitudinal groove are visible. The cerebellum possesses in
its interior a cavity which communicates with the anterior part of
the fourth ventricle. The _medulla oblongata_ is broader than the
spinal chord, and contains the _fourth ventricle_, which forms the
continuation of the central canal of the spinal chord. In most fishes
a perfect roof is formed over the fourth ventricle by two longitudinal
pads, which meet each other in the median line (_lobi posteriores_),
and but rarely it remains open along its upper surface.

The brain of _Ganoid fishes_ shows great similarity to that of the
Teleostei; however, there is considerable diversity of the arrangement
of its various portions in the different types. In the Sturgeons and
_Polypterus_ (Fig. 42) the hemispheres are more or less remote from
the mesencephalon, so that in an upper view the crura cerebri, with
the intermediate entrance into the third ventricle (_fissura cerebri
magna_), may be seen. A vascular membranous sac, containing lymphatic
fluid (_epiphysis_), takes its origin from the third ventricle, its
base being expanded over the anterior interspace of the optic lobes,
and the apex being fixed to the cartilaginous roof of the cranium.
This structure is not peculiar to the Ganoids, but found in various
stages of development in Teleosteans, marking, when present, the
boundary between prosencephalon and mesencephalon. The lobi optici
are essentially as in Teleosteans. The cerebellum penetrates into
the ventriculus lobi optici, and extends thence into the open sinus
rhomboidalis. At its upper surface it is crossed by a commissure formed
by the _corpora restiformia_ of the medulla.

  [Illustration: Fig. 42.--Brain of Polypterus. (After Müller.)

  I., Upper; II., Lateral; III., Lower aspect.

    _a_, Medulla; _b_, corpora restiformia; _c_, cerebellum;
    _d_, lobi optici; _e_, hypophysis; _f_, fissura cerebri
    magna; _g_, nervus opticus; _g_’, chiasma; _h_, hemispheres;
    _i_, lobus olfactorius; _k_, sinus rhomboidalis (fourth
    ventricle).]

As regards external configuration, the brain of _Lepidosteus_
and _Amia_ approach still more the Teleosteous type. The
prosencephalon, mesencephalon, and metencephalon are contiguous, and
the cerebellum lacks the prominent transverse commissure at its upper
surface. The sinus rhomboidalis is open.

The brain of the _Dipnoi_ shows characters reminding us of that of
the Ganoids as well as the Chondropterygians, _Ceratodus_ agreeing
with _Protopterus_ in this respect, as in most other points of
its organisation. The hemispheres form the largest part of the brain;
they are coalescent, as in Sharks, but possess two lateral ventricles,
the separation being externally indicated by a shallow median groove
on the upper surface. The olfactory lobes take their origin from
the upper anterior end of the hemispheres. Epiphysis and hypophysis
well developed. The lobi optici are very small, and remote from the
prosencephalon, their division into the lateral halves being indicated
by a median groove only. The cerebellum is very small, overlying the
front part of the sinus rhomboidalis.

  [Illustration: Fig. 43.--Brain of Carcharias. (After Owen.)

    _ac_, Nerv. acusticus; _b_, corpus restiforme; _c_,
    cerebellum; _d_, lobus opticus; _e_, hypophysis; _g_, nervus
    opticus; _h_, hemisphere; _i_, lobus olfactorius; _i’_,
    olfactory pedicle; _k_, nerv. olfactorius; _l_, epiphysis;
    _m_, nerv. oculo-motorius; _tr_, nerv. trigeminus; _v_, nerv.
    vagus.]

The brain of _Chondropterygians_ (Fig. 43) is more developed than
that of all other fishes, and distinguished by well-marked characters.
These are, first, the prolongation of the olfactory lobes into more or
less long pedicles, which dilate into great ganglionic masses, where
they come into contact with the olfactory sacs; secondly, the space
which generally intervenes between prosencephalon and mesencephalon, as
in some Ganoids; thirdly, the large development of the metencephalon.

The hemispheres are generally large, coalescent, but with a median,
longitudinal, dividing groove. Frequently their surface shows traces
of gyrations, and when they are provided with lateral ventricles,
tubercles representing _corpora striata_ may be observed. The
olfactory pedicles take their origin from the side of the hemispheres,
and are frequently hollow, and if so, their cavity communicates with
the ventricle of the hemisphere. The optic lobes are generally smaller
than the hemispheres, coalescent, and provided with an upper median
groove like the prosencephalon. At their base a pair of lobi inferiores
are constant, with the hypophysis and _sacsus vasculosus_ (a
conglomeration of vascular loops without medullary substance) between
them.

The cerebellum is very large, overlying a portion of the optic lobes
and of the sinus rhomboidalis, and is frequently transversely grooved.
The side-walls of the fourth ventricle, which are formed by the corpora
restiformia, are singularly folded, and appear as two pads, one on
each side of the cerebellum (_lobi posteriores_ s. _lobi nervi
trigemini_).

  [Illustration: Fig. 44.--Brain of Bdellostoma. (Enlarged, after
  Müller.)

    I., Upper; II., Lower aspect.      Letters as in Fig. 45.]

  [Illustration: Fig. 45.--Brain of Petromyzon. (Enlarged, after
  Müller.)

  I., Upper; II., Lower aspect.

    _a_, Medulla oblongata; _ac_, nerv. acusticus; _b_, corpus
    restiforme or rudimentary cerebellum; _d_, lobus ventriculi
    tertii; _d’_, entrance into the third ventricle; _c_,
    hypophysis; _fa_, nerv. facialis; _g_, nerv. opticus;
    _h_, hemisphere; _hy_, nerv. hypoglossus (so named by
    Müller); _i_, lobus olfactorius; _k_, sinus rhomboidalis;
    _l_, epiphysis; _m_, nerv. oculo-motorius; _q_, corpora
    quadrigemina; _tr_, nerv. trigeminus; _tro_, nerv.
    trochlearis; _v_, nerv. vagus.]

The brain of the _Cyclostomes_ (Figs. 44, 45) represents a type
different from that of other fishes, showing at its upper surface
three pairs of protuberances in front of the cerebellum; they are
all solid. Their homologies are not yet satisfactorily determined,
parts of the Myxinoid brain having received by the same observers
determinations very different from those given to the corresponding
parts of the brain of the Lampreys. The foremost pair are the large
olfactory tubercles, which are exceedingly large in _Petromyzon_. They
are followed by the hemispheres, with a single body wedged in between
their posterior half; in _Petromyzon_, at least, the vascular tissue
leading to an epiphysis seems to be connected with this body. Then
follows the lobus ventriculi tertii, distinctly paired in Myxinoids,
less so in _Petromyzon_. The last pair are the _corpora quadrigemina_.
According to this interpretation the cerebellum would be absent in
Myxinoids, and represented in _Petromyzon_ by a narrow commissure
only (Fig. 45, _b_), stretching over the foremost part of the sinus
rhomboidalis. In the Myxinoids the _medulla oblongata_ ends in two
divergent swellings, free and obtuse at their extremity, from which
most of the cerebral nerves take their origin.


The _Nerves_ which supply the organs of the head are either merely
continuations or diverticula of the brain-substance, or proper nerves
taking their origin from the brain, or receiving their constituent
parts from the foremost part of the spinal chord. The number of these
spino-cerebral nerves is always less than in the higher vertebrates,
and their arrangement varies considerably.


     A. _Nerves which are diverticula of the brain_ (Figs. 41–45).

The _olfactory_ nerves (_first pair_) always retain their intimate
relation to the hemispheres, the ventricles of which are not rarely
continued into the tubercle or even pedicle of the nerves. The
different position of the olfactory tubercle has been already described
as characteristic of some of the orders of fishes. In those fishes
in which the tubercle is remote from the brain, the nerve which has
entered the tubercle as a single stem leaves it split up into several
or numerous branches, which are distributed in the nasal organ. In
the other fishes it breaks up into branchlets spread into a fan-like
expansion at the point, where it enters the nasal cavity. The nerve
always passes out of the skull through the ethmoid.

The _optic_ nerves (_second pair_) vary in size, their strength
corresponding to the size of the eye; they take their origin from the
_lobi optici_, the development of which again is proportionate to that
of the nerves. The mutual relation of the two nerves immediately after
their origin is very characteristic of the sub-classes of fishes. In
the _Cyclostomes_ they have no further connection with each other, each
going to the eye of its own side.[11] In the _Teleostei_ they simply
cross each other (_decussate_), so that the one starting from the right
half of the brain goes to the left eye and _vice versa_. Finally, in
_Palæichthyes_ the two nerves are fused together, immediately after
their origin, into a _chiasma_. The nerve is cylindrical for some
portion of its course, but in most fishes gradually changes this
form into that of a plaited band, which is capable of separation and
expansion. It enters the bulbus generally behind and above its axis.
The foramen through which it leaves the skull of Teleostei is generally
in a membranous portion of its anterior wall, or, where ossification
has taken place, in the orbito-sphenoid.


         B. _Nerves proper taking their origin from the brain_
                            (Figs. 41–45).

The _Nervus oculorum motorius_ (_third pair_) takes its origin from
the Pedunculus cerebri, close behind the lobi inferiores; it escapes
through the orbito-sphenoid, or the membrane replacing it, and is
distributed to the musculi rectus superior, rectus internus, obliquus
inferior, and rectus inferior. Its size corresponds to the development
of the muscles of the eye. Consequently it is absent in the blind
_Amblyopsis_, and the Myxinoids. In _Lepidosiren_ the nerves supplying
the muscles of the eye have no independent origin, but are part of the
ophthalmic division of the Trigeminus. In _Petromyzon_ these muscles
are supplied partly from the Trigeminus, partly by a nerve representing
the Oculo-motor and Trochlearis, which are fused into a common trunk.

The _Nervus trochlearis_ (_fourth pair_), if present with an
independent origin, is always thin, taking its origin on the upper
surface of the brain from the groove between lobus opticus and
cerebellum; it goes to the Musculus obliquus superior of the eye.


      C. _Nerves taking their origin from the Medulla oblongata_
                            (Figs. 41–45).

The _Nervus abducens_ (_sixth pair_) issues on the lower surface of
the brain, taking its origin from the anterior pyramids of the Medulla
oblongata, and supplies the Musculus rectus externus of the eye, and
the muscle of the nictitating membrane of Sharks.

The _Nervus trigeminus_ (_fifth pair_) and the _Nervus facialis_
(_seventh pair_) have their origins close together, and enter into
intimate connection with each other. In the Chondropterygians and
most Teleostei the number of their roots is four, in the Sturgeons
five, and in a few Teleostei three. When there are four, the first
issues immediately below the cerebellum from the side of the Medulla
oblongata; it contains motory and sensory elements for the maxillary
and suspensorial muscles, and belongs exclusively to the trigeminal
nerve. The second root, which generally becomes free a little above
the first, supplies especially the elements for the Ramus palatinus,
which sometimes unites with parts of the Trigeminal, sometimes with the
Facial nerve. The third root, if present, is very small, and issues
immediately in front of the acustic nerve, and supplies part of the
motor elements of the facial nerve. The fourth root is much stronger,
sometimes double, and its elements pass again partly into the
Trigeminal, partly into the Facial nerve. On the passage of these stems
through the skull (through a foramen or foramina in the alisphenoid)
they form a ganglionic plexus, in which the palatine ramus and the
first stem of the Trigeminus generally possess discrete ganglia.
The branches which issue from the plexus and belong exclusively to
the Trigeminus, supply the organs and integuments of the frontal,
ophthalmic, and nasal regions, and the upper and lower jaws with their
soft parts. The Facial nerve supplies the muscles of the gill-cover
and suspensorium, and emits a strong branch accompanying the Meckelian
cartilage to the symphysis, and another for the hyoid apparatus.

The _Nervus acusticus_ (_eighth pair_) is strong, and takes its origin
immediately behind, and in contact with, the last root of the seventh
pair.

The _Nervus glossopharyngeus_ (_ninth pair_)[12] takes its origin
between the roots of the eighth and tenth nerves, and issues in
Teleostei from the cranial cavity by a foramen of the exoccipital. In
the Cyclostomes and Lepidosiren it is part of the Nervus vagus. It is
distributed in the pharyngeal and lingual regions, one branch supplying
the first branchial arch. After having left the cranial cavity it
swells into a ganglion, which in Teleostei is always in communication
with the sympathic nerve.

The _Nervus vagus_ or _pneumogastricus_ (_tenth pair_) rises in
all Teleostei and Palæichthyes with two discrete strong roots: the
first constantly from the swellings of the corpora restiformia, be
they thinner or thicker and overlying the sinus rhomboidalis, or
be they developed into lateral plaited pads, as in Acipenser and
Chondropterygians. The second much thicker root rises from the lower
tracts of the medulla oblongata. Both stems leave the cranial cavity by
a common foramen, situated in Teleosteous fishes in the exoccipital;
and form ganglionic swellings, of which those of the lower stem are the
more conspicuous. The lower stem has mixed elements, motory as well as
sensory, and is distributed to the muscles of the branchial arches and
pharynx, the œsophagus and stomach; it sends filaments to the heart and
to the air-bladder where it exists. The first (upper) stem forms the
_Nervus lateralis_. This nerve, which accompanies the lateral mucous
system of the trunk and tail, is either a single longitudinal stem,
gradually becoming thinner behind, running superficially below the
skin (Salmonidæ, Cyclopterus), or deeply between the muscles (Sharks,
Chimæra), or divided into two parallel branches (most Teleostei): thus
in the Perch there are two branches on each side, the superficial
of which supplies the lateral line, whilst the deep-seated branch
communicates with the spinal nerves and supplies the septa between the
myocommas and the skin. In fishes which lack the lateral muciferous
system and possess hard integuments, as the Ostracions, the lateral
nerve is more or less rudimentary. It is entirely absent in Myxinoids,
but the gastric branches of the Vagus are continued, united as a single
nerve, along the intestine to the anus.

No fish possesses a _Nervus accessorius_. Also a separate _Nervus
hypoglossus_ (_twelfth pair_)[13] is absent, but elements from the
first spinal nerve are distributed in the area normally supplied by
this nerve in higher vertebrates.

       *       *       *       *       *

The number of _Spinal_ nerves corresponds to that of the vertebræ,
through or between which they pass out. Each nerve has two roots,
an anterior and posterior, the former of which has no ganglion, and
exclusively contains motor elements. The posterior or dorsal has a
ganglionic enlargement, and contains sensory elements only. After
leaving the vertebral canal each spinal nerve usually divides into
a dorsal and ventral branch. The Gadoids show that peculiarity that
each of the posterior roots of some or many of the spinal nerves
possesses two separate threads, each of which has a ganglion of its
own; the one of these threads joins the dorsal and the other the
ventral branch. In fishes in which the spinal chord is very short, as
in Plectognaths, Lophius, the roots of the nerves are extremely long,
forming a thick _Cauda equina_. The additional function which
the (five) anterior spinal nerves of _Trigla_ have to perform
in supplying the sensitive pectoral appendages and their muscles has
caused the development of a paired series of globular swellings of the
corresponding portion of the spinal chord. A similar structure is found
in _Polynemus_.

  [Illustration: Fig. 46.

   Brain and anterior portion of the spinal chord of Trigla
   (Gurnard), showing the globular swellings at the base of the
   anterior spinal nerves.]

A _Sympathic nervous_ system appears to be absent in _Branchiostoma_,
and has not yet been clearly made out in _Cyclostomes_. It is well
developed in the _Palæichthyes_, but without cephalic portion. This
latter is present in all Osseous fishes, in which communication of the
Sympathic has been found to exist with all cerebral nerves, except the
olfactory, optic, and acustic. The sympathic trunks run along each
side of the aorta and the back of the abdomen into the hæmal canal;
communicate in their course with the ventral branches of each of the
spinal nerves; and, finally, often blend together into a common trunk
beneath the tail. At the points of communication with the cerebral
and spinal nerves frequently ganglia are developed, from which nerves
emerge which are distributed to the various viscera.




                             CHAPTER VII.

                         THE ORGANS OF SENSE.


Characteristic of the _Organ of Smell_ in Fishes is that it has
no relation whatever to the respiratory function, with the exception
of the _Dipnoi_, in which possibly part of the water received for
respiration passes through the nasal sac.

The olfactory organ is single in _Branchiostoma_ and the _Cyclostomes_.
In the former a small depression on the front end of the body, clothed
with a ciliated epithelium, is regarded as a rudimentary organ of
smell. In the adult _Petromyzon_ a membranous tube leads from the
single opening on the top of the head into the cartilaginous olfactory
capsule, the inside of which is clothed by membranes prolonged into a
posterior blind tube (Fig. 30, _s_), which penetrates the cartilaginous
roof of the palate, but not the mucous membrane of the buccal cavity.
In the Myxinoids the outer tube is strengthened by cartilaginous
rings like a trachea; the capsule is lined by a longitudinally folded
pituitary membrane, and the posterior tube opens backwards on the roof
of the mouth; the opening is provided with a valve.

In all other Fishes the organ of smell is double, one being on each
side; it consists of a sac lined with a pituitary membrane, and
without, or with one or two, openings. The position of these openings
is very different in the various orders or suborders of Fishes.

In the _Dipnoi_ the nasal sac opens downwards by two wide openings
which are within the boundaries of the cavity of the mouth. The
pituitary membrane is transversely folded, the transverse folds being
divided by one longitudinal fold. The walls of the sac are strengthened
by sundry small cartilages.

Also in _Chondropterygians_ the openings, of which there is one
to each sac, are on the lower part of the snout, and in the Rays,
Holocephali, and some Sharks, each extends into the cleft of the mouth.
The openings are protected by valvular flaps, supported by small
cartilages, and moved by muscles, whence it may be concluded that these
fishes are able to scent (actively) as well as to smell (passively).

  [Illustration: Fig. 47.--Nostrils of _Raia lemprieri_, with
  nasal flaps reverted.]

In the majority of _Teleostei_ the olfactory capsules are lateral or
superior on the snout, covered externally by the skin, each usually
pierced by two openings, which are either close together, or more
or less remote from each other; the posterior is generally open,
the anterior provided with a valve or tube. In the _Chromides_ and
_Labroidei ctenoidei_ a single opening only exists for each sac. In
the _Murænidæ_ the two openings of each side are either superior, or
lateral, or labial, that is, they are continued downwards and pierce
the margin of the upper lip. In many Tetrodonts nasal openings are
absent, and replaced by a conical papilla, in which the olfactory nerve
terminates.

It is certain that fishes possess the faculty of perceiving odours,
and that various scents attract or repel them. A mangled carcase
or fresh blood attracts Sharks as well as the voracious Serrasal
monoids of the South American rivers. There is no reason to doubt that
the seat of that perception is in the olfactory sac; and it may be
reasonably conjectured that its strength depends mainly on the degree
of development indicated by the number and extent of the interior folds
of the pituitary membrane.

_Organ of Sight_.--The position, direction, and dimensions of the
eyes of fishes vary greatly. In some they have an upward aspect, and
are often very close together; in others they are lateral, and in a
few they are even directed downwards. The Flat-fishes represent the
extraordinary anomaly that both eyes are on the same side of the head,
and rarely on the same level, one being generally placed more forward
than the other. In certain species of marine fishes the eyes are of
an extraordinary size, a peculiarity indicating that the fish either
lives at a great depth, to which only a small proportion of the rays
of light penetrate, or that it is of nocturnal habits. In fishes which
have descended to such great depths that no rays whatever can reach
them, or in freshwater fishes living in caves, or in species which
grovel and live constantly in mud, the eyes are more or less aborted,
sometimes quite rudimentary, and covered by the skin. In very few this
organ appears to be entirely absent. In some Gobioids and Trachinoids
(_Periophthalmus_, _Boleophthalmus_, _Uronoscopus_, etc.) the eyes,
which are on the upper side of the head, can be elevated and depressed
at the will of the fish. In the range of their vision and acuteness of
sight, Fishes are very inferior to the higher classes of Vertebrates,
yet at the same time it is evident that they perceive their prey or
approaching danger from a considerable distance; and it would appear
that the visual powers of a _Periophthalmus_, when hunting insects on
mud-flats of the tropical coasts, are quite equal to that of a frog.
Again, the discrimination with which fishes sometimes prefer one colour
or kind of artificial fly to another affords sufficient evidence
that the vision, at least of certain species is by no means devoid of
clearness and precision.

The eye of _Branchiostoma_ is of the most rudimentary condition. It is
simply a minute speck coated by dark pigment, and receiving the end of
a short nerve. In _Myxinoids_ the minute rudiment of the eye is covered
by the skin and muscles. This is also the case in many of the blind
Teleosteous fishes; however, whilst in the former fishes the organ of
sight has not attained to any degree of development, the rudimentary
eye of blind Teleostei is a retrogressive formation, in which often
a lens and other portions of the eye can be recognised. In fishes
with a well-developed eye it is imbedded in a layer of gelatinous and
adipose substance, which covers the cavity of the orbit. A lacrymal
gland is absent. In the orbit of one fish only, _Chorismodentex_, an
organ has been found which can be compared to a _saccus lacrymalis_.
It is a round, blind, wide sac, of the size of a pea, situated below
the anterior corner of the orbit, between the maxillary bone and the
muscles of the cheek, communicating by a rather wide foramen with
the orbital cavity. The membrane by which it is formed is continuous
with that coating the orbita. In the Chondropterygians the eyeball is
supported by and moves on a cartilaginous peduncle of the orbital wall.
In the majority of Teleosteans, and in Acipenser, a fibrous ligament
attaches the sclerotic to the wall of the orbit. The proper muscles
of the eyeball exist in all fishes, and consist of the four _Musculi
recti_ and the two _M. obliqui_. In many Teleostei the former rise
from a subcranial canal, the origin of the _M. rectus externus_ being
prolonged farthest backwards. The _Recti_ muscles are extraordinarily
long in the Hammerheaded Sharks, in which they extend from the basis
cranii along the lateral prolongations of the head to the eyes, which
are situated at the extremities of the hammer.

In all fishes the general integument of the head passes over the
eye, and becomes transparent where it enters the orbit; sometimes it
simply passes over the orbit, sometimes it forms a circular fold. The
anterior and posterior portions may be especially broad and the seat
of an adipose deposit (_adipose eyelids_), as in _Scomber_, _Caranx_,
_Mugil_, etc. In many of these fishes the extent of these eyelids
varies with the seasons; during the spawning season they are so much
loaded with fat as nearly to hide the whole eye. Many Sharks possess a
_nictitating_ membrane, developed from the lower part of the palpebral
fold, and moved by a proper set of muscles.

  [Illustration: Fig. 48.

   Vertical section through eye of Xiphias. (After Owen.)

    _co_, Cornea; _sc_, sclerotica; _o_, nervus opticus; _c_,
    sclerotic capsule; _a_, membrana argentea; _v_, membrana
    vasculosa; _u_, membrana uvea; _ch_, choroid gland; _r_,
    retina; _f_, processus falciformis; _h_, humor vitreus; _l_,
    lens; _i_, iris.]

The form of the _bulbus_ (Fig. 48) is subhemispherical, the cornea
(_co_) being flat. If it were convex, as in higher Vertebrates, it
would be more liable to injury; but being level with the side of the
head the chances of injury by friction are diminished. The _sclerotica_
(_sc_) is cartilaginous in Chondropterygians and Acipensers, fibrous
and of varying thickness in Teleosteans, in the majority of which it
is supported by a pair of cartilaginous or ossified hemispheroid cups
(_c_). In a few fishes, as in _Ceratodus_, _Xiphias_, the cups are
confluent into one cup, which possesses a foramen behind to allow the
passage of the optic nerve (_o_). The _cornea_ of _Anableps_ shows an
unique peculiarity. It is crossed by a dark horizontal stripe of the
conjunctiva, dividing it into an upper and lower portion; also the iris
is perforated by two pupils. This fish is observed to swim frequently
with half of its head out of the water, and it is a fact that it can
see out of the water as well as in it.

The membranes situated between the sclerotica and retina are
collectively called _choroidea_, and three in number. The one in
immediate contact with the sclerotic, and continued upon the iris,
is by no means constantly present; it is the _membrana argentea_
(_a_), and composed of microscopical crystals reflecting a silvery or
sometimes golden lustre. The middle layer is the _membrana vasculosa_
s. _halleri_ (_v_), the chief seat of the ramifications of the choroid
vessels; the innermost layer is the _membrana ruyscheana_ or _uvea_
(_u_), which is composed of hexagonal pigment-cells, usually of a deep
brown or black colour.

In many _Teleostei_ a _rete mirabile_ surrounds the entry of the optic
nerve; it is situated between the membrana argentea and vasculosa, and
called the _choroid gland_ (_ch_). It receives its arterial blood from
the artery issuing from the pseudobranchia; the presence of a choroid
gland always being combined with that of a pseudobranchia. Teleosteans
without pseudobranchia lack a choroid gland. In the Palæichthyes, on
the other hand, the pseudobranchia is present and a choroid gland
absent.

The _iris_ (_i_) is merely the continuation of the choroid membrane;
its capability of contracting and expanding is much more limited than
in higher Vertebrates. The _pupil_ is generally round, sometimes
horizontally or vertically elliptical, sometimes fringed. In the
Rays and Pleuronectidæ a lobe descends from the upper margin of the
pupil, and the outer integument overlying this lobe is coloured and
non-transparent; a structure evidently preventing light from entering
the eye from above.

In most _Teleostei_ a fold of the _Choroidea_, called the _Processus
falciformis_ (_f_), extends from the vicinity of the entrance of the
optic nerve to the lens. It seems to be constantly absent in Ganoids.

The _retina_ (_r_) is the membrane into which the optic nerve
penetrates, and in which its terminal filaments are distributed. It
consists of several layers (Fig. 49). The outermost is an extremely
delicate membrane (_a_), followed by a layer of nerve-cells (_b_), from
which the terminal filaments issue, passing through several granular
strata (_c_, _d_, _e_), on which the innermost stratum rests. This
stratum is composed of cylindrical rods (_f_) vertically arranged,
between which twin fusiform corpuscles (_g_) are intercalated. This
last layer is thickly covered with a dark pigment. The retina extends
over a portion of the iris, and a well-defined raised rim runs along
its anterior margin.

  [Illustration: Fig. 49.--Vertical section of the Retina of the
  Perch, magn. X 350.]

The _vitreous humour_ (Fig. 48, _h_) which fills the posterior
cavity of the eyeball, is of a firmer consistency than in the higher
Vertebrates. The _lens_ is spherical, or nearly so; firm, denser
towards the centre, and lies in a hollow of the vitreous humour. When
a falciform process is present, it is with one end attached to the
lens, which is thus steadied in its position. It consists of concentric
layers consisting of fibres, which in the nucleus of the body have
marginal teeth, by which they are interlocked together. In _Petromyzon_
this serrature is absent, or but faintly indicated.

  [Illustration: Fig. 50.--Interlocking fibres of lens, highly
  magnified.]

The anterior cavity of the eye is very small in Fishes, in consequence
of the small degree of convexity of the cornea; the quantity of the
aqueous humour, therefore, is very small, just sufficient to float the
free border of the iris; and the lessened refractive power of the
aqueous humour is compensated by the greater convexity of the lens.

       *       *       *       *       *

_Organ of Hearing._--No trace of an organ of hearing has been found
in _Branchiostoma_. In the _Cyclostomes_ the labyrinth is enclosed in
externally visible cartilaginous capsules laterally attached to the
skull; it consists of a single _semicircular canal_ in the Myxinoids,
whilst the Petromyzontes possess two semicircular canals with a
_vestibulum_.

In all other fishes the labyrinth consists of a vestibule and three
semicircular canals, the vestibule dilating into one or more sacs which
contain the otoliths. A tympanum, tympanic cavity, and external parts,
are entirely absent in the class of fishes.

In the _Chondropterygians_ and _Dipnoi_, the labyrinth is enclosed in
the cartilaginous substance of the skull. In the former the excavation
in the cartilage is larger than the membranous labyrinth, but nearly
corresponds to it in form; the part which receives the membranous
vestibulum is called _Vestibulum cartilagineum_, from which a canal
issues and penetrates to the surface of the skull, where it is closed
by the skin in Sharks, but opens by a minute foramen in Rays. The
otolithic contents are soft and chalklike.

In the _Holocephali_ part of the labyrinth is enclosed in the cartilage
of the skull, another part being in the cranial cavity, as in Ganoids
and Teleosteans. The membranous vestibulum is continued by a canal to a
single opening in the roof of the skull, from which two smaller canals
are continued to two small foramina in the skin covering the occipital
region.

In the _Teleosteans_ the sac which contains the otoliths lies on each
side of the base of the cranial cavity and is often divided by a septum
into two compartments of unequal size, each containing a firm and solid
_otolith_; these bodies (Fig. 51), possess indented margins, frequently
other impressions and grooves, in which nerves from the N. acusticus
are lodged; they vary much in size and form, but in both respects show
a remarkable constancy in the same kind of fishes. The vestibule is
outwards in contact with the osseous side wall of the skull, inwards
with the metencephalon and medulla oblongata; it contains another firm
concretion, and opens by five foramina into the three semicircular
canals. The terminations of the acustic nerve are distributed over the
vestibular concretion and the ampulliform ends (Fig. 52 _p_) of the
semicircular canals, without being continued into the latter, which are
filled with fluid. The semicircular canals (Fig. 52 _g_), are sometimes
lodged in the cranial bones, sometimes partly free in the cranial
cavity. Many Teleostei have fontanelles in the roof of the skull,
closed by skin or very thin bone only at the place where the auditory
organ approaches the surface, by which means sonorous undulations must
be conducted with greater ease to the ear.

  [Illustration:

   Fig. 51.--Otolith of Haddock (Gadus æglefinus). I. Outer, II.
   Inner aspect.]

In many Teleostei a most remarkable relation obtains between the organ
of hearing and the air-bladder. In the most simple form this connection
is established in Percoids and the allied families, in which the two
anterior horns of the air-bladder are attached to fontanelles of the
occipital region of the skull, the vestibulum occupying the opposite
side of the membrane by which the fontanelle is closed. The condition
is similar, but more complicated in many Clupeoids. The anterior narrow
end of the air-bladder is produced into a canal at the base of the
skull, and divided into two very narrow branches, which again bifurcate
and terminate in a globular swelling. An appendage of the vestibulum
meets the anterior of these swellings, and comes into close contact
with it. Besides, the two vestibules communicate with each other by a
transverse canal, crossing the cranial cavity below the brain.

  [Illustration: Fig. 52.--Communication between auditory organ and
  air-bladder in the Carp. (After E. H. Weber.)

    _a_, Basisphenoid; _b_, Occipital; _c_, Supraoccipital;
    _d_, Exoccipital; _e_, Paroccipital; _f_, Alisphenoid; _g_,
    Neural arch of first vertebra; _h_, _i_, _k_, second, third,
    and fourth vertebra; _h_’, _i_’, Parapophyses of second and
    third vertebra; _i_", process of the third vertebra for
    the attachment of the air-bladder; _k_, _l_, _m_, Chain
    of ossicles; _n_, Air-bladder; _o_, vestibulum; _p_, _p_,
    Ampullæ; _q_, _q_, Canales semicirculares; _r_, Sinus impar.]

The connection is effected by means of a chain of ossicles in
_Siluridæ_, _Characinidæ_, _Cyprinidæ_ and _Gymnotidæ_. A canal issues
from the communication between vestibule and its sac, and meeting that
from the other side forms with it a common _sinus impar_ (Fig. 52,
_r_), lodged in the substance of the basi-occipital; this communicates
on each side by a small orifice with two subspherical atria, on
the body of the atlas, close to the foramen magnum. Each atrium is
supported externally by a small bone (_m_); a third larger bone (_k_)
completes the communication with the anterior part of the air-bladder.
From the sinus impar a bifid canal penetrates into the alisphenoids,
in which it terminates. In _Cobitis_ and several Loach-like Siluroids
the small air-bladder consists of two globular portions placed side
by side, and wholly included within two bullæ, formed by the modified
parapophyses of the second and third vertebræ. The three ossicles on
each side are present, but concealed by the fore part of the osseous
bulla.

       *       *       *       *       *

_Organ of Taste._--Some fishes, especially vegetable feeders, or those
provided with broad molar-like teeth, masticate their food; and it
may be observed in Carps and other Cyprinoid fish, that this process
of mastication frequently takes some time. But the majority of fish
swallow their food rapidly, and without mastication, and therefore we
may conclude that the sense of taste cannot be acute. The tongue is
often entirely absent, and even when it exists in its most distinct
state, it consists merely of ligamentous or cellular substance, and
is never furnished with muscles capable of producing the movements of
extension or retraction as in most higher Vertebrates. A peculiar organ
on the roof of the palate of Cyprinoids, is perhaps an organ adapted
for perception of this sense; in these fishes the palate between and
below the upper pharyngeal bones is cushioned with a thick, soft
contractile substance, richly supplied with nerves from the Nervi vagus
and glossopharyngeus.

_Organs of Touch._--The faculty of touch is more developed than that of
taste, and there are numerous fishes which possess special organs of
touch. Most fishes are very sensitive to external touch, although their
body may be protected by hard horny scales. They perceive impressions
even on those parts which are covered by osseous scutes, in the same
manner as a tortoise perceives the slightest touch of its carapace. The
seat of the greatest sensitiveness, however, appears to be the snout
and the labial folds surrounding the mouth. Many species possess soft
and delicate appendages, called barbels, which are almost constantly
in action, and clearly used as organs of touch. Among the _Triglidæ_
and allied families, there are many species which have one or more
rays of the pectoral fin detached from the membrane, and supplied with
strong nerves. Such detached rays (also found in the _Polynemidæ_,
_Bathypterois_) are used partly for locomotion, partly for the purpose
of exploring the ground over which the fish moves.

Some fish appear to be much less sensitive than others, or at least
lose their sensitiveness under peculiar circumstances. It is well known
that a Pike, whose mouth has been lacerated and torn by the hook,
continues to yield to the temptation of a bait immediately afterwards.
The Greenland Shark when feeding on the carcass of a whale allows
itself to be repeatedly stabbed in the head without abandoning its
prey. A pair of Congers are so dead to external impression at the time
of copulation, and so automatically, as it were, engaged, that they
have been taken by the hand together out of the water.




                             CHAPTER VIII.

                THE ORGANS OF NUTRITION AND DIGESTION.


Fishes are either exclusively carnivorous or herbivorous, but not a few
feed on vegetable substances as well as animal, or on mud containing
alimentary substance in a living or decomposing state. Generally they
are very voracious, especially the carnivorous kinds, and the rule of
“eat or be eaten” applies to them with unusual force. They are almost
constantly engaged in the pursuit and capture of their prey, the
degree of their power in these respects depending on the dimensions
of the mouth and gullet and the strength of the teeth and jaws. If
the teeth are sharp and hooked, they are capable of securing the most
slender and agile animals; if this kind of teeth is combined with a
wide gullet and distensible stomach, they are able to overpower and
swallow other fish larger than themselves; if the teeth are broad,
strong molars, they are able to crush the hardest aliments; if they
are feeble, they are only serviceable in procuring some small or inert
and unresisting prey. Teeth may be wanting altogether. Whatever the
prey, in the majority of cases it is swallowed whole; but some of the
most voracious fishes, like some Sharks and _Characinidæ_, are
provided with cutting teeth, which enable them to tear their prey to
pieces if too large to be swallowed whole. Auxiliary organs for the
purpose of overpowering their prey, which afterwards is seized or torn
by the teeth, like the claws of some carnivorous mammals and birds, are
not found in this class; but in a few fishes the jaws themselves are
modified for that purpose. In the Sword-fishes the bones of the upper
jaw form a long dagger-shaped weapon, with which they not only attack
large animals, but also frequently kill fishes on which they feed.
The Saw-fishes are armed with a similar but still more complicated
weapon, the saw, which is armed on each side with large teeth implanted
in deep sockets, specially adapted for killing and tearing the prey
before it is seized and masticated by the small teeth within the mouth.
Fishes show but little choice in the selection of their food, and some
devour their own offspring indiscriminately with other fishes. Their
digestive powers are strong and rapid, but subject in some degree to
the temperature, which, when sinking below a certain point, lowers the
vital powers of these cold-blooded animals. On the whole, marine fishes
are more voracious than those inhabiting fresh waters; and whilst the
latter may survive total abstinence from food for weeks or months,
the marine species succumb to hunger within a few days. The growth of
fishes depends greatly on the nature and supply of food, and different
individuals of the same species may exhibit a great disparity in their
respective dimensions. They grow less rapidly and to smaller dimensions
in small ponds or shallow streams than in large lakes and deep rivers.
The young of coast fishes, when driven out to sea, where they find
a much smaller supply of food, remain in an undeveloped condition,
assuming an hydropic appearance. The growth itself seems to continue
in most fishes for a great length of time, and we can scarcely set
bounds to--certainly we know not with precision--the utmost range of
the specific size of fishes. Even among species in no way remarkable
for their dimensions we sometimes meet with old individuals, favourably
situated, which more or less exceed the ordinary weight and measurement
of their kind. However, there are certain evidently short-lived species
of fishes which attain a remarkably uniform size within a very short
time; for instance, the Stickleback, many species of _Gobius_ and
_Clupea_.

       *       *       *       *       *

The organs of nutrition, manducation, and deglutition, are lodged in
two large cavities--an anterior (the mouth or _buccal cavity_), and
a posterior (the _abdominal cavity_). In the former the alimentary
organs are associated with those fulfilling the respiratory functions,
the transmission of food to the stomach and of water to the gills
being performed by similar acts of deglutition. The abdominal cavity
commences immediately behind the head, so, however, that an extremely
short thoracic cavity for the heart is partitioned off in front. Beside
the alimentary organs it contains also those of the urogenital system
and the air-bladder. The abdominal cavity is generally situated in the
trunk only, but in numerous fishes it extends into the tail, being
continued for some distance along each side of the hæmal apophyses.

In numerous fishes the abdominal cavity opens outwards by one or two
openings. A single _porus abdominalis_ in front of the vent is found
in _Lepidosiren_ and some Sturgeons; a paired one, one on each side
of the vent, in _Ceratodus_, some species of Sturgeon, _Lepidosteus_,
_Polypterus_, _Amia_, and all Chondropterygians. As in these fishes
semen and ova are discharged by proper ducts, the abdominal openings
may serve for the expulsion of semen, and those ova only which, having
lost their way to the abdominal aperture of the oviduct, would be
retained in the abdominal cavity. In those _Teleosteans_ which lack an
oviduct a single _porus genitalis_ opens _behind_ the vent.

The _mouth_ of fishes shows extreme variation with regard to form,
extent, and position. Generally opening in front, it may be turned
upwards, or may lie at the lower side of the snout, as in most
Chondropterygians, Sturgeons, and some Teleosteans. Vogt regards this
position as a persistent fœtal condition. In most fishes the jaws are
covered by the skin, which, before passing over the jaws, is often
folded, forming more or less fleshy lips. In the Sharks the skin
retains its external character even within the teeth, but in other
fishes it changes into a mucous membrane. A _tongue_ may exist as a
more or less free and short projection, formed by the glosso*-hyal and
a soft covering, or may be entirely absent. _Salivary_ glands and a
_velum palati_ are absent in fishes.

With regard to the _dentition_, the class of Fishes offers an amount
of variation such as is not found in any of the other classes of
Vertebrates. As the teeth form one of the most important elements in
the classification of fishes, their special arrangement and form will
be referred to in the account of the various families and genera.
Whilst not a few fishes are entirely edentulous, in others most of the
bones of the buccal cavity, or some of them, may be toothed, as the
bones of the jaws, the palatines, pterygoids, vomers, basisphenoid,
glossohyal, branchial arches, upper and lower pharyngeals. In others
teeth may be found fixed in some portion of the buccal membrane without
being supported by underlying bone or cartilage; or the teeth have
been developed in membrane overlying one of the dentigerous bones
mentioned, without having become anchylosed to the bone. When the tooth
is fixed to the bone the attachment has generally been effected by the
ossification of the bone of the tooth, but in some fishes a process of
the bone projects into the cavity of the tooth; in others the teeth are
implanted in alveoli. In these, again, frequently a process of bone
rises from the bottom, on which the tooth rests.

Many fishes, especially predatory fishes with long, lancet-shaped
teeth, have all or some of the teeth capable of being bent inwards
towards the mouth. Such “hinged” teeth resume at once the upright
position when pressure is removed from them. They are, however,
depressible in one direction only, thus offering no obstacle to the
ingress, but opposing the egress of prey. Mr. C. S. Tomes has shown
that the means by which this mechanism is worked are different in
different fishes; for whilst, in the _Pediculati_ and _Gadoids_ (Hake)
the elasticity resides solely in the tissue of the hinge (the tooth
being as resilient as ever after everything else is severed), in the
Pike the hinge is not in the least endowed with elasticity, but the
bundles of fibres proceeding from the interior of the dentine cap are
exceedingly elastic.

As regards texture the teeth of fishes show considerable variation.
The conical teeth of the Cyclostomes and the setiform teeth of many
Teleosteans consist of a horny albuminous substance. The principal
substance of the teeth of other fishes consists of dentine, with
numerous dividing and anastomosing tubercles, sometimes covered by
a stratum of unvascular dentine. An enamel-like substance has been
observed on the crown of the teeth of _Sargus_ and _Balistes_, and an
ossification of the capsule of their matrix covers the enamel with a
thin coating of cement. The teeth either possess a cavity in which the
matrix is received, or, more frequently, they are solid, in which case
vascular canals of the underlying bone are continued into the substance
of the tooth. In the teeth of some fishes numerous sets of canals and
tubes are so arranged that they do not anastomose with one another,
each set being surrounded by a layer of dentine and cement. These
apparently simple teeth are evidently composed of numerous small teeth,
and called _compound_ teeth.

The teeth may be, and generally are, very different as regards size or
form in the different parts of the mouth; they may be also different
according to the age or sex of the fish (_Raja_). The teeth may be few
in number and _isolated_, or placed in a single, double, or triple
_series_, _distant_ from one another or _closely set_; they may form
narrow or broad _bands_, or _patches_ of various forms. As regards
form, they may be cylindrical or conical, pointed, straight, or curved,
with or without an angular bent near their base; some are compressed
laterally or from the front backwards; the latter may be triangular
in shape, or truncated at the top like incisors of mammals; they may
have one apex (cusp) only, or be bi- or tri-lobate (bi- or tri-cuspid);
or have the margins denticulated or serrated. Compressed teeth may be
confluent, and form a cutting edge in both jaws, which assume the shape
of a parrot’s beak (Fig. 53). In some the apex is hooked or provided
with barbs. Again, some teeth are broad, with flat or convex surface,
like molar teeth. With regard to size, the finest teeth are like fine
flexible bristles, _ciliiform_ or _setiform_; or, if very short and
anchylosed to the bone, they appear only as inconspicuous asperities
of the bone. Very fine conical teeth arranged in a band are termed
_villiform_ teeth; when they are coarser, or mixed with coarser teeth,
they are _card-like_ (dents en rape or en cardes) (Fig. 54); molar-like
teeth of very small size are termed _granular_.

  [Illustration: Fig. 53.--Jaws of Calliodon.]

In all fishes the teeth are constantly shed or renewed during the
whole course of their life. In fishes which have compound teeth, as
the Dipnoi, Chimæroids, Scari,[14] Gymnodonts, as well as in those
which have apparently permanent teeth, as in the saw of _Pristis_,
the detrition of the surface is made up by a constant growth of the
tooth from its base. When the teeth are implanted in alveoli, they
are generally succeeded by others in the vertical direction, but in
others they succeed one another, side by side. In the majority of
fishes the new tooth is not developed (as in reptiles and mammals) in
a diverticulum of the sack of its predecessor, but like this from the
free surface of the buccal membrane. Generally there are more than one
tooth growing, which are in various stages of development, and destined
to replace the one in function. This is very conspicuous in Sharks,
in which the whole phalanx of their numerous teeth is ever marching
slowly forwards (or in some backwards), in rotatory progress, over the
alveolar border of the jaw, the teeth being successively cast off after
having reached the outer margin, and fulfilled for a longer and shorter
period their special function.

   [The richest materials for our knowledge of the teeth of fishes
   are contained in _Owen’s_ “Odontography.” Lond. 1840. 8vo.]

  [Illustration: Fig. 54.--Cardlike teeth of Plectropoma dentex,
  with canines.]

The _intestinal tract_ is divided into four portions: œsophagus,
stomach, small and large intestine; two or more of these divisions
may coalesce in fishes and become indistinguishable. But it is
characteristic of the class that the urinary apertures are constantly
situated behind the termination of the intestinal tract.

In _Branchiostoma_ the whole intestinal tract is straight, and
coated with a ciliated mucous membrane. The wide pharynx passes into a
narrow œsophagus, this into a gastric cavity, the remainder being again
narrower and terminating in the anal aperture, which lies somewhat
to the left of the median line. The liver is represented by a green
coloured cœcal diverticulum of the stomachic dilatation. A mesenterium
is absent.

In the _Cyclostomi_ the intestinal tract is likewise straight, and
without clearly defined divisions; however, in _Petromyzon_ the
œsophagus shows numerous longitudinal folds, and the intestine proper
is provided with a single longitudinal fold. A mesentery, which is
present in the Myxinoids, is represented by a short median fold only,
by means of which the hindmost part of the intestine is fixed.

The _Palæichthyes_ show differences in the structure of their
intestinal tract as considerable as are found among the _Teleostei_,
but they have that in common that the absorbent surface of their
intestine is enlarged by the development of a spiral valve, evidence
of the presence of which in extinct Palæichthyes is still preserved in
the fossilised fæces or _coproliths_, so abundant in some of the older
strata.

In _Chondropterygians_ (Fig. 55) the stomach is divided into a cardiac
and pyloric portion, the former frequently terminating in a blind
sac, and the latter varying in length. The pyloric portion is bent
at its origin and end, and separated from the short duodenum (called
_Bursa entiana_ in these fishes) by a valve; the ductus hepaticus and
pancreaticus enter the duodenum. This is succeeded by the straight
intestine provided with the spiral valve, the coils of which may
be either longitudinal and wound vertically about the axis of the
intestine, as in _Carcharias_, _Galeocerdo_, _Thalassorhinus_, and
_Zygœna_, or they may be transverse to that axis, as in the other
genera. The number of gyrations in the latter case varies: there may be
as many as forty. The short rectum passes into a cloaca, which contains
also the orifices of the urogenital ducts. Only the commencement and
end of the intestinal tract are fixed by mesenterial folds.

In the _Holocephali_ and _Dipnoi_, the intestinal tract is short,
straight, and wide, without stomachic dilatation, a pyloric valve,
close to which the ductus choledochus enters, indicating the boundary
of the intestine proper (Fig. 57, _p_). The spiral valve is perfect,
and makes from three (_Chimæra_) to nine (_Ceratodus_) gyrations. A
cloaca is present, as in Chondropterygians. A mesentery fixing the
dorsal side of the intestine is absent.

  [Illustration: Fig. 55.--Siphonal stomach and spiral valve of
  Basking-Shark (Selache). (After Home and Owen.)

    _a_, Œsophagus; _b_, Cardiac portion of stomach; _c_,
    pyloric portion; _d_, pouch intermediate between stomach and
    duodenum, with circular valves at both ends; _e_, Duodenum;
    _f_, Valve of intestine; _g_, Ductus hepaticus; _h_, Spleen.]

The other _Ganoids_ resemble again more the Chondropterygians
in the structure of their intestinal tract. The stomach has always a
distinct pyloric portion, and has a still more complicated structure
in _Acipenser_. The duodenal portion receives the contents of
_Appendices pyloricæ_, which are confluent into a gland-like mass
in _Acipenser_, but separate in _Polyodon_, and numerous and
short in _Lepidosteus_, whilst _Polypterus_ possesses one
such appendage only. A spiral valve is developed in the Sturgeons and
Polypterus, but in _Amia_, in which the intestine performs several
convolutions, the four gyrations of the valve are situated far back
towards the end of the intestine. In _Lepidosteus_ the valve is
rudimentary, and indicated only by three raised lines crossing the
terminal portion of the intestine. In all these Ganoids the rectum has
a separate opening, without cloaca.

The structure of the intestinal tract of _Teleosteous_ fishes is
subject to so numerous modifications that we should go beyond the
limits of the present work if we would attempt to enter into details.
Great differences in this respect may be found even in groups of the
same natural families. Frequently the intestinal tract remains of
nearly the same width throughout its course, and only the entrance
of the various ducts serves as a guide for the distinction of its
divisions. An intestine of such uniform width may be straight and
short, as in _Scombresocidæ_, _Symbranchidæ_, or it may be more or less
convoluted and long, as in many _Cyprinidæ_, _Doradina_, etc. On the
whole, carnivorous fishes have a much shorter and simpler intestinal
tract than herbivorous.

In the majority of Teleosteans, however, œsophagus, stomach, duodenum,
small intestine and rectum, can be more or less distinctly, even
externally distinguished.

There are two predominant forms of the stomach, intermediate forms
being, however, numerous. In the first, the _siphonal_, it
presents the form of a bent tube or canal, one-half of the horse-shoe
being the cardiac, the other the pyloric portion. In the second, the
_cæcal_, the cardiac division is prolonged into a long descending
blind sac, the cardiac and pyloric openings of the stomach lying close
together (_Clupea_, _Scomber_, _Thynnus_, etc.)

  [Illustration: Fig. 56.--Siphonal Stomach and Pyloric Appendages
  of a Female Salmon, 3⅓ feet long. _a a a_, Pyloric appendages;
  _ch_, ductus choledochus; _oe_, œsophagus; _st_, lower end
  of stomach; _p_, pyloric region; _i_, ascending; and _í’_,
  descending portion of intestine.]

The duodenum receives always the hepatic and pancreatic secretions,
and, besides, those of the appendices pyloricæ, which, in varying
numbers (from 1 to 200), are of very common occurrence in Teleosteans
(Fig. 56). They vary also in length and width, and whilst the
narrowest serve only as secretory organs, the widest are frequently
found filled with the same contents as the intestine. When few in
number, each opens by a separate duct into the duodenum; when their
number is greater two or more coalesce into a common duct; in the
latter case the appendages cease to be free, and are connected with one
another by a more or less firm tissue.

Cœcal appendages at the end of the intestinal tract are of exceedingly
rare occurrence in fishes (_Box_). There is no _cloaca_ in Teleosteans.

In the majority of Teleosteous fishes the _vent_ is situated on the
boundary between trunk and tail, behind the ventral fins. In a few it
lies farther backwards, not far from the caudal fin; more frequently
it is advanced forwards, under the middle of the abdomen or to the
scapular arch. In two fishes, _Aphredoderus_ and _Amblyopsis_, it lies
before the pectoral fins.

A peritoneum envelops all the divisions of the intestinal tract within
the abdominal cavity. A broad, well-developed _omentum_ has hitherto
been found in _Gobiesox cephalus_ only.

_Liver_.--The existence of a liver in _Branchiostoma_ as a long
diverticulum of the intestine has been mentioned above. In the
Myxinoids the liver is divided into two glandular bodies, an anterior
rounded smaller one, and a posterior larger one of an elongate shape.
The gall-bladder lies between both, and receives a cystic duct from
each of them. In the other fishes the proportionally large liver is a
single large gland, from which only now and then small portions are
found to be detached. It is either simple, or with a right and left
lobe, or with a third lobe in the middle; each lobe may have incisions
or subdivisions, which, however, are very inconstant. The liver of
fishes is distinguished by the great quantity of fluid fat (oil) which
it contains. The gall-bladder is but rarely absent, and attached to
the right lobe, or towards the centre; however, in some fishes it
is detached from the liver and connected with it by the cystic duct
only. The bile may be conveyed by one or more hepatic ducts into a
common duct which is continued towards the gall-bladder as _ductus
cysticus_, and towards the duodenum as _ductus choledochus_; or some
of the hepatic ducts enter directly the gall-bladder, or directly
the duodenum, without communicating with the common duct. Individual
variations in this respect are of common occurrence.

A _pancreas_ has been found hitherto in all Chondropterygians,
Acipenser, and many Teleosteans. In the first it is a glandular mass
of considerable size behind the stomach, close to the spleen; its duct
leads into the duodenum. In the Sturgeons the pancreas is attached to
the duodenum, and opens close to the ductus choledochus. In _Silurus
glanis_ it is very large, and the ductus choledochus passes through
its substance; it is smaller in _Belone_ and _Pleuronectes_, and
situated in the mesentery; its duct accompanies the terminal portion
of the ductus choledochus. In the Salmon, which possesses a large
lobed pancreas, the duct is so intimately connected with the ductus
choledochus that both appear externally as a single duct only.

The _spleen_, which is substantially a lymphatic gland, may be
mentioned here, as it is constantly situated in the immediate vicinity
of the stomach, generally near its cardiac portion. With the exception
of _Branchiostoma_, it is found in all fishes, and appears as a rounded
or oblong organ of dark-red colour. In the Sharks frequently one or
more smaller pieces are detached from the principal body. In the Dipnoi
a thin layer of a very soft substance of brownish-black colour below
the mucous membrane of the stomach and upper part of the intestine has
been regarded as the homologue of the spleen (Fig. 57, _m_). In most
_Teleostei_ the spleen is undivided, and appended by its vessels and
a fold of the peritoneum to the pyloric bend of the stomach or the
beginning of the intestine.

  [Illustration: Fig. 57.--Upper part of Intestine of Ceratodus.
  The anterior wall of the intestine is opened, the liver (_c_) and
  gall-bladder (_e_) being drawn forward. A slit is made at _n_,
  through which part of the next compartment of the spirally wound
  intestine may be seen.

  _é_, Mouth of ductus choledochus; _f_, stomach; _i_, adipose
  agglomeration; _l_, first compartment of intestinal spire; _m_,
  spleen; _oe_, lower part of œsophagus, opened; _p_, double
  pyloric fold; _q_ _q_, glandular patches.]




                              CHAPTER IX.

                        ORGANS OF RESPIRATION.


Fishes breathe the air dissolved in water by means of gills or
branchiæ. The oxygen consumed by them is not that which forms the
chemical constituent of the water, but that contained in the air which
is dissolved in water. Hence fishes transferred into water from which
the air has been driven out by a high temperature, or in which the
air absorbed by them is not replaced, are speedily suffocated. The
absorption of oxygen by fishes is comparatively small, and it has been
calculated that a man consumes 50,000 times more than is required by
a Tench. However, some fishes evidently require a much larger supply
of oxygen than others: Eels and Carps, and other fishes of similar
low vitality, can survive the removal out of their elements for days,
the small quantity of moisture retained in their gill-cavity being
sufficient to sustain life, whilst other fishes, especially such as
have very wide gill-openings, are immediately suffocated after being
taken out of the water. In some fishes noted for their muscular
activity, like the _Scombridæ_, the respiratory process is so
energetic as to raise the temperature of their blood far beyond that
of the medium in which they live. A few fishes, especially such as
are periodically compelled to live in water thickened into mud by
desiccation and vitiated by decomposing substances, breathe atmospheric
air, and have generally special contrivances for this purpose. These
are so much habituated to breathing air that many of them, even when
brought into pure water of normal condition, are obliged to rise
to the surface at frequent intervals to take in a quantity of air,
and if they be kept beneath the surface by means of a gauze net,
they perish from suffocation. The special contrivances consist of
additional respiratory organs, lodged in cavities either adjoining the
gill-cavity or communicating with the ventral side of the œsophagus,
or of the air-bladder which enters upon respiratory functions (Dipnoi,
Lepidosteus, Amia).

The water used by fishes for respiration is received by the mouth, and
by an action similar to that of swallowing driven to the gills, and
expelled by the gill-openings, of which there may be one or several on
each side behind the head; rarely one only in the median line of the
ventral surface.

  [Illustration: Fig. 58.--Fore-part of the body of an embryon of
  Carcharias, showing the branchial filaments (natural size).]

The _gills_ or _branchiæ_ consist essentially of folds of the mucous
membrane of the gill-cavity (_laminæ branchiales_), in which the
capillary vessels are distributed. In all fishes the gills are lodged
in a cavity, but during the embryonic stage the Chondropterygians have
the gill-laminæ prolonged into long filaments projecting beyond the
gill-cavity (Fig. 58), and in a few young Ganoids external gills are
superadded to the internal.

In _Branchiostoma_ the dilated pharynx is perforated by numerous
clefts, supported by cartilaginous rods (Fig. 29, _h_). The water
passes between these clefts into the peritoneal cavity, and makes its
exit by the porus abdominalis situated considerably in advance of the
vent. The water is propelled by cilia.

In the _Cyclostomes_ the gills of each side are lodged in a series of
six or more antero-posteriorly compressed sacs, separated from each
other by intervening septa. Each sac communicates by an inner duct
with the œsophagus, the water being expelled by an outer duct. In
_Bdellostoma_ each outer duct has a separate opening, but in _Myxine_
all the outer ducts pass outwards by one common gill-opening on each
side. In the Lampreys the ducts are short, the outer ones having
separate openings (Fig. 2, p. 39). The inner ducts lead into a single
diverticulum or bronchus, blind behind, situated below the œsophagus,
and communicating in front with the pharynx, where it is provided with
two valves by which the regurgitation of the water into the buccal
cavity is prevented.

The same type of branchial organs persists in _Chondropterygians_,
which possess five, rarely six or seven, flattened pouches with
transversely plaited walls. The septa between them are supported by
cartilaginous filaments rising from the hyoidean and branchial arches.
Each pouch opens by a cleft outwards, and by an aperture into the
pharynx, without intervening ducts. The anterior wall of the first
pouch is supported by the hyoidean arch. Between the posterior wall
of the first and the anterior of the second sac, and between the
adjacent walls of the succeeding, a branchial arch with its two series
of radiating cartilaginous filaments is interposed. Consequently the
first and last pouch have one set of gill-laminæ only, viz. the first
on its posterior and the last on its anterior wall. The so-called
_spiracles_ on the upper surface of the head of Chondropterygians are
to be referred to in connection with the respiratory organs. They are
the external openings of a canal leading on each side into the pharynx,
and situated generally close to and behind the orbit. They frequently
possess valves or an irregularly indented margin, and are found in all
species during the embryonic stage, but remaining persistent in a part
only. The spiracles are the remains of the first visceral cleft of
the embryo, and in the fœtal state long branchial filaments have been
observed to protrude, as from the other branchial clefts.

The _Holocephali_ and _Ganoidei_ show numerous deviations from the
Chondropterygian type, all leading in the direction towards the
Teleosteans. As a whole they take an intermediate position between the
preceding types and the Teleosteans, but they show a great variation
among themselves, and have in common only the imperfect separation
of the branchial sacs and the presence of a single outer branchial
aperture.

In _Chimæra_ the septum separating the branchial sacs is confluent
with the wall of the gill-cavity in a part of its extent only, and
still more imperfect is the separation of those branchial divisions
in _Ceratodus_ (Fig. 60). The other Ganoids show no such division
whatever. In _Chimæra_ the first gill is incomplete (uniserial), and
belongs to the hyoid; then follow three complete gills; the last,
belonging to the fourth branchial arch, being again incomplete.
_Acipenser_, _Scaphirhynchus_, _Lepidosiren_, _Protopterus_,
and _Lepidosteus_, possess likewise an anterior incomplete gill
(_opercular gill_), followed by four complete gills in the Sturgeons
and _Lepidosteus_, whilst in _Lepidosiren_ and _Protopterus_ a part
of the branchial arches is gill-less. In _Polyodon_, _Ceratodus_, and
_Polypterus_, an opercular gill is absent, the two former having four
complete gills, the latter three and a half only. _Spiracles_ are still
in some Ganoids present, viz. in the Sturgeons and _Polypterus_. In all
the Ganoids an osseous gill-cover is now developed.

In the _Teleostei_ the gills with their supporting branchial arches
lie in one undivided cavity; more or less wide clefts between the
arches lead from the pharynx to the gills, and a more or less wide
opening gives exit to the water after it has washed the gills. The
interbranchial clefts have sometimes nearly the same extent as the
branchial arches; sometimes they are reduced to small openings, the
integuments stretching from one arch to the other. Sometimes there
is no cleft behind the fourth arch, in which case this arch has only
an uniserial gill developed. The gill-opening likewise varies much
in its extent, and when reduced to a foramen may be situated at any
place of the posterior boundary of the head. In the _Symbranchidæ_
the gill-openings coalesce into a single narrow slit in the median
line of the isthmus. In the majority of Teleosteans the integument of
the concave side of the branchial arches develops a series of horny
protuberances of various form, the so-called _gill-rakers_. They are
destined to catch any solid corpuscles or substances which would be
carried into the gill-cavity with the water. In some fishes they are
setiform, and form a complete sieve, whilst in others they are merely
rough tubercles, the action of which must be very incomplete if they
have any function at all.

Most Teleosteans possess four complete gills, but frequently the
fourth arch is provided with an uniserial gill only, as mentioned
above, or even entirely gill-less. The most imperfect gills are found
in _Malthe_, which has two and a half gills only, and in _Amphipnous
cuchia_, in which one small gill is fixed to the second arch.

The gills of the Teleosteans as well as of the Ganoids are supported by
a series of solid cartilaginous or horny pointed rods, arranged along
the convex edges of the branchial arches. Arches bearing a complete
gill have two series of those rods, one along each edge; those with
uniserial gills bear one row of rods only. The rods are not part
of the arch, but fixed in its integument, the several rods of one
row corresponding to those of the other, forming pairs (_feuillet_,
Cuvier) (Fig. 59). Each rod is covered by a loose mucous membrane
passing from one rod to its fellow opposite, which again is finely
transversely plaited, the general surface being greatly increased by
these plaits. In most Teleostei the branchial lamellæ are compressed,
and taper towards their free end, but in the Lophobranchs their base
is attenuated and the end enlarged. The mucous membrane contains the
finest terminations of the vessels, which, being very superficial,
impart the blood-red colour to living gills. The _Arteria branchialis_,
the course of which lies in the open canal in the convexity of the
branchial arch, emits a branch (_a_) for every pair of lamellæ which
ascends (_b_) along the inner edge of the lamella, and supplies every
one of the transverse plaits with a branchlet. The latter break up into
a fine net of capillaries, from which the oxygenised blood is collected
into venous branchlets, returning by the venous branch (_d_), which
occupies the outer edge of the lamella.

  [Illustration:

   Fig. 59.--A pair of branchial lamellæ (magnified) of the Perch.

    _a_, Branch of Arteria branchialis; _b_, Ascending branch of
    the same; _c_, Branch of Vena branchialis; _d_, Descending
    branch of the same; _e_, Transverse section through the
    branchial arch.]

The so-called _Pseudobranchiæ_ (Fig. 60) are the remains of an anterior
gill which had respiratory functions during the embryonic life of the
individuals. By a change in the circulatory system these organs have
lost those functions, and appear in the adult fish as retia mirabilia,
as they receive oxygenised blood, which, after having passed through
their capillary system, is carried to other parts of the head. In
Palæichthyes the pseudobranchia is a rete mirabile caroticum for the
brain and eye; in Teleosteans a rete mirabile ophthalmicum only.
Pseudobranchiæ are as frequently absent as present in Chondropterygians
as well as Teleosteans. As to the Ganoids, they occur in _Ceratodus_,
_Acipenser_, _Polyodon_, and _Lepidosteus_, and are absent in
_Lepidosiren_, _Protopterus_, _Scaphirhynchus_, _Polypterus_, and
_Amia_.

In Chondropterygians and Sturgeons the pseudobranchiæ are situated
within the spiracles; in those, in which spiracles have become
obliterated, the pseudobranchiæ lie on the suspensorium, hidden below
cellular tissue; but pseudobranchiæ are not necessarily co-existent
with spiracles. In the other Ganoids and Teleosteans the pseudobranchiæ
(Fig. 60, _h_) are within the gill-cavity, near the base of the
gill-cover; in _Ceratodus_ even rudiments of the gill-rakers (_x’_,
_x”_) belonging to this embryonic gill are preserved, part of them
(_x”_) being attached to the hyoid arch. Pseudobranchiæ are frequently
hidden below the integuments of the gill-cavity, and have the
appearance of a glandular body rather than of a gill.

   [See Müller, “Vergleichende Anatomie des Gefäss-systems der
   Myxinoiden;” and “Ueber den Bau und die Grenzen der Ganoiden.”]

  [Illustration: Fig. 60.--Gills of Ceratodus.

    _x_, Arcus aortæ; _gl_, Glossohyal; _ch_, Ceratohyal; _u_,
    Attachment of the first gill to the walls of the gill-cavity;
    _h_, Pseudobranchia; _x’_, _x”_, two series of gill-rakers
    belonging to the Pseudobranchia.]

_Accessory respiratory organs_ for retaining water or breathing air,
such as are found in the _Labyrinthici_, _Ophiocephalidæ_, certain
_Siluridæ_, and _Lutodira_, are structures so specialised that they are
better described in the accounts of the Fishes in which they have been
observed.

       *       *       *       *       *

_Air-Bladder._--The air-bladder, one of the most characteristic organs
of fishes, is a hollow sac, formed of several tunics, containing gas,
situated in the abdominal cavity, but without the peritoneal sac,
entirely closed or communicating by a duct with the intestinal tract.
Being compressible, its special functions consist in altering the
specific gravity of the fish or in changing the centre of gravity. In a
few fishes it assumes the function of the organ of higher Vertebrates,
of which it is the homologue--viz. of a _lung_.

The gas contained in the air-bladder is secreted from its inner
surface. In most freshwater fishes it consists of nitrogen, with a very
small quantity of oxygen and a trace of carbonic acid; in sea-fishes,
especially those living at some depth, oxygen predominates, as much
as 87 per cent having been found. Davy found in the air-bladder of a
fresh-run Salmon a trace of carbonic acid and 10 per cent of oxygen,
the remainder of the gas being nitrogen.

An air-bladder is absent in _Leptocardii_, _Cyclostomi_,
_Chondropterygii_, and _Holocephali_; but occurs in all Ganoids, in
which, besides, its respiratory functions more or less clearly manifest
themselves. Its occurrence in Teleosteans is most irregular, closely
allied species sometimes differing from each other in this respect; it
shows in this sub-class the most extraordinary modifications, but has
no respiratory function whatever.

Constantly situated within the abdominal cavity, below the vertebral
column, but without the sac of the peritoneum which covers only its
ventral portion, the air-bladder is frequently prolonged into the
tail, the prolongation being either simple and lodged between the
non-united parapophyses, or double and penetrating between the muscles
and hæmapophyses of each side. In the opposite direction processes of
the air-bladder may penetrate into the skull, as has been mentioned
above (p. 117). In some fishes the air-bladder is almost loose in the
abdominal cavity, whilst in others it adheres most intimately by firm
and short tissue to the vertebral column, the walls of the abdomen, and
the intestines. In the Cobitina and many Siluroids it is more or less
completely enclosed in osseous capsules formed by the vertebræ.

The tunics of the majority of air-bladders are an extremely fine
internal one, frequently shining silvery, containing crystalline
corpuscles, sometimes covered with a pavement-epithelium; and a thicker
outer one of a fibrous texture, which sometimes attains to considerable
thickness and yields isinglass. This wall is strengthened in many
fishes by muscular layers for the compression of the whole organ or of
some portion of it.

A distinction has been made between air-bladders which communicate by
a duct with the intestinal tract and those which are entirely closed.
However, it is to be remembered that at an early stage of development
all air-bladders are provided with such a duct, which in a part of the
fishes more or less completely obliterates, being then represented by
a fine ligament only. In young _Lucioperca_ of six to eight inches in
length the duct may be found still open for a considerable distance;
and, on the other hand, in adult _Physostomi_, that is Teleosteous
fishes with a ductus pneumaticus, not rarely the whole duct is found
very narrow, or, for some part of its length, even entirely closed.

  [Illustration: Fig. 61.--Air-bladder of Otolithus sp.]

  [Illustration:

    Fig. 62.--Vertical section through abdominal cavity of
    Collichthys lucida. _b_, air-bladder; _l_, liver; _s_,
    stomach; _epp_ and _ipp_, external and internal laminæ of
    peritoneum parietale; _epv_ and _ipv_, external and internal
    laminæ of peritoneum viscerale; _dv_, dorsal air-vessels;
    _vv_, ventral air-vessels.]

Air-bladders without duct are found in Acanthopterygians,
Pharyngognaths, Anacanths, and Lophobranchs. They may consist of
a single cavity or divided by constrictions into two or three
partitions situated behind one another; they may consist of two lateral
partitions, assuming a horseshoe-like form, or they may be a single
sac with a pair of simple or bifid processes in front or behind (Fig.
61). The families of _Sciænidæ_ and _Polynemidæ_ possess air-bladders
with a most extraordinary development of appendages rising from each
side of the air-bladder. In the Sciænoid (Fig. 63) fifty-two branches
issue from each side, each branch being bifurcate and bearing smaller
appendages. In _Pogonias chromis_ (Fig. 64) the sides of the anterior
half is provided with irregular broad-fringed appendages, the hindmost
of which communicates by a narrow duct with the posterior extremity
of the air-bladder. In _Collichthys lucida_ (Fig. 62) twenty-five
appendages issue from each side; the anterior ones are directed towards
the front, but the lateral assume a more posterior direction, the
nearer they are to the posterior extremity of the air-bladder, where
they form an assemblage giving the appearance of a cauda equina. All
these appendages soon bifurcate in a dorsal and ventral stem; these
stems bifurcate again and again, and either terminate after the first
or second bifurcation or are so far prolonged as to reach the median
line of the ventral and dorsal sides, anastomosing with the branches
of the other side. The branches being enveloped in laminæ of the
peritonæum, form a dorsal and ventral sac of beautiful appearance,
caused by the regular arrangement of the air-vessels. The dorsal sac is
situated between the air-bladder and the roof of the abdominal cavity
without being attached to the latter. The ventral sac receives within
its cavity the intestine, liver, and ovaries.--A peculiar mechanism
has been observed in the air-bladder of the _Ophidiidæ_, the anterior
portion of which can be prolonged by the contraction of two muscles
attached to its anterior extremity, with or without the addition of a
small bone.

  [Illustration: Fig. 63.--Air-bladder of a Sciænoid.

   I. Visceral surface opened at _b_, to show openings of the
   lateral branches.

   II. Isolated lateral branch; _a_, its opening into the
   cavity of the air-bladder.]

Air-bladders with a pneumatic duct are found in Ganoids and
Physostomes, the duct entering the dorsal side of the intestinal
tract, with the exception of _Polyp__terus_ and the _Dipnoi_, in
which it enters on the ventral side of the œsophagus. In the majority
the orifice is in the œsophagus, but in some, as in _Acipenser_, in
the cardiac portion of the stomach, or in its blind sac, as in many
Clupeoids. The air-bladder may be single, or consist of two divisions
situated one behind the other (Fig. 52); its inner surface may be
perfectly smooth, or form manifold pouches and cells. If two divisions
are present the anterior possesses a middle elastic membrane which
is absent in the posterior; each division has a muscular layer, by
which it can be separately compressed, so that part of the contents of
the posterior may be driven into the elastic anterior division, and
_vice versa_. The posterior division being provided with the ductus
pneumaticus does not require the elasticity of the anterior.

  [Illustration: Fig. 64.--Air-bladder of Pogonias chromis.]

Some Siluroids possess a peculiar apparatus for voluntarily exercising
a pressure upon the air-bladder. From the first vertebra a process
takes its origin on each side, expanding at its end into a large round
plate; this is applied to the side of the air-bladder, and by pressing
upon it expels the air through the duct; the small muscle moving the
plate rises from the skull.

The connection of the air-bladder with the organ of hearing in some
Physostomes has been described above, p. 117.

In the modifications of the air-bladder, hitherto mentioned, the
chief and most general function is a mechanical one; this organ
serves to regulate the specific gravity of the fish, to aid it in
maintaining a particular level in the water, in rising or sinking,
in raising or depressing the front part of its body as occasion may
serve. Yet a secretion of gas from the blood into its cavity must take
place; and if this be so, it is not at all impossible that also an
exchange of gases between the two kinds of blood is effected by means
of the extraordinary development of _retia mirabilia_ in many
air-bladders.

In all fishes the arteries of the air-bladder take their origin from
the aorta or the system of the aorta, and its veins return either to
the portal, or vertebral, or hepatic veins; like the other organs of
the abdominal cavity it receives arterial blood and returns venous
blood. However, in many fishes the arteries as well as veins break
up below the inner membrane into _retia mirabilia_ in various ways.
The terminal ramifications of the arteries may dissolve into fan-like
tufts of capillaries over almost every part of the inner surface,
as in Cyprinoids. Or these tufts of radiating capillaries are more
localised at various places, as in _Esocidæ_; or the tufts are so
aggregated as to form gland-like, _red bodies_, the capillaries
reuniting into larger vessels, which again ramify freely round the
border of the red body; the red bodies are formed not only by minute
arteries but also by minute veins, both freely anastomosing with
its kind, and being inextricably interwoven. The rest of the inner
surface of the air-bladder receives its blood, not from the red bodies,
but from normally ramifying vessels. This kind of rete mirabile or
“vaso-ganglion” is found in the Perch and Gadoids; it is generally
distributed in closed air-bladders, but also sometimes observed in
air-bladders’ with pneumatic duct. In _Anguilla_ and _Conger_ two
similar vaso-ganglia are situated at the sides of the opening of the
pneumatic duct.

  [Illustration: Fig. 65.--Lung of Ceratodus opened in its lower
  half to show its cellular pouches. _a_, Right half; _b_, Left
  half; _c_, Cellular pouches; _e_, Vena pulmonalis; _f_, Arterial
  blood-vessel; _oe_, Œsophagus opened, to show glottis (_gl._)]

Whilst the air-bladders of some _Ganoids_, anatomically as well as
functionally, closely adhere to the Teleosteous type, that of _Amia_
is more cellular and lung-like in its interior than the Teleosteous
air-bladder, and _Polypterus_ approaches the Dipnoi not only in
having a laterally divided air-bladder but also in its pneumatic duct
entering the _ventral_ side of the œsophagus. The air-bladder of the
_Dipnoi_ possesses still more the anatomical characteristics of a lung
and assumes its functions, though, as it co-exists with gills, only
periodically or in an auxiliary manner. The ductus pneumaticus is a
membranous bronchus, entering the ventral side of the œsophagus, and
provided at its entrance with a _glottis_. In _Ceratodus_ (Fig. 65) the
lung is still a single cavity, but with a symmetrical arrangement of
its internal pouches; it has no pulmonal artery, but receives branches
from the _arteria cœliaca_. Finally, in _Lepidosiren_ and _Protopterus_
the lung is completely divided into lateral halves, and by its cellular
structure approaches most nearly that of a reptile; it is supplied with
venous blood by a true pulmonary artery.

  [Illustration: Fig. 66.--Heart of Lepidosteus osseus.

  I. External aspect. II. Conus arteriosus opened.

    _a_, Atrium; _b_, Conus arteriosus; _v_, Ventricle; _h_,
    Branchial artery for 3d and 4th gill; _k_, for the second;
    _l_, for the first; _m_, branch for the opercular gill; _d_,
    Single valve at the base of the conus; _e-g_, Transverse rows
    of Ganoid valves.]




                              CHAPTER X.

                        ORGANS OF CIRCULATION.


The _Blood-corpuscles_ of fishes are, with one exception, of an
elliptic shape; this exception is _Petromyzon_, which possesses
circular, flat, or slightly biconvex blood-corpuscles. They vary much
in size; they are smallest in Teleosteans and Cyclostomes, those of
_Acerina cernua_ measuring 1/2461 of an inch in their longitudinal, and
1/3000 in their transverse diameter. As far as it is known at present
the _Salmonidæ_ have the largest blood-corpuscles among Teleosteans,
those of the salmon measuring 1/1524 by 1/2460 in., approaching those
of the Sturgeon. Those of the Chondropterygians are still larger; and
finally, _Lepidosiren_ has blood-corpuscles not much smaller than those
of Perennibranchiates, viz.--1/570 by 1/941 in. Branchiostoma is the
only fish which does not possess red blood-corpuscles.

   [See G. Gulliver, “Proc. Zool. Soc.,” 1862, p. 91; and 1870, p.
   844; and 1872, p. 833.]

Fishes, in common with the other Vertebrates, are provided with a
complete circulation for the body, with another equally complete for
the organs of respiration, and with a particular abdominal circulation,
terminating at the liver by means of the _vena portæ_; but their
peculiar character consists in this, that the branchial circulation
alone is provided at its base with a muscular apparatus or _heart_,
corresponding to the right half of the heart of Mammalia and Birds.

The _Heart_ is situated between the branchial and abdominal cavities,
between the two halves of the scapulary arch, rarely farther behind,
as in _Symbranchidæ_. It is enclosed in a _pericardium_, generally
entirely separated from the abdominal cavity by a diaphragma, which
is, in fact, the anterior portion of the peritoneum, strengthened
by aponeurotic fibres. However, in some fishes there is a
communication between the pericardial and peritoneal sacs, viz. in
the Chondropterygians and Acipenser, whilst in the Myxinoids the
pericardial sac is merely a continuation of the peritoneum.

  [Illustration: Fig. 67.--Heart of Ceratodus.

    _a_, Atrium; _b_, Conus arteriosus; _d_, Papillary valve
    within the conus; _e-g_, Transverse rows of Ganoid valves;
    _h_, _i_, Anterior arcus aortæ; _k_, _l_, Posterior arcus
    aortæ; _v_, Ventricle.]

The heart is, relatively to the size of the body, very small, and
consists of three divisions: the _atrium_, with a large _sinus
venosus_ into which the veins enter; the _ventricle_; and a conical
hollow swelling at the beginning of the arterial system, the structure
of which forms one of the most important characters used in the
classification of fishes. In all _Palæichthyes_ (Figs. 66 and 67) this
swelling is still a division of the pulsating heart, being provided
with a thick muscular stratum; it is not separated from the ventricle
by two valves opposite to each other, but its interior is fitted with
a plurality of valves, arranged in transverse series more or less
numerous in the various groups of _Palæichthyes_. _Lepidosiren_ and
_Protopterus_ offer an example of a modification of this valvular
arrangement, their valves being longitudinal, each valve in fact being
formed by the confluence of several smaller ones situated behind one
another. This Palæichthyan type is called _conus arteriosus_.

In Cyclostomes and Teleosteans (Fig. 68) the enlargement is a swelling
of the artery, without muscular stratum and without contractility; with
the exception of the Myxinoids its walls are thick, fibrous, with many
trabeculæ and pouches, but it has no valves in its interior, and is
separated from the ventricle by two valves opposite to each other. This
Teleostean type is called _bulbus aortæ_.

  [Illustration: Fig. 68.--Bulbus aortæ of Xiphias gladius, opened.

    _a_, Section through part of the wall of ventricle; _b_,
    Section through the bulbus; _c_, Teleosteous valves of the
    ostium arteriosum; _d_, Accessory valves, of rudimentary
    nature and inconstant; _e_, Trabeculæ carneæ of the bulbus.]

The sinus venosus sends the whole of the venous blood by a single
orifice of its anterior convexity into the atrium; two thin membranous
valvules turned towards the atrium, prevent the blood from re-entering
the sinus. A pair of other valves between atrium and ventricle have the
same function. The walls of the ventricle are robust, and, internally,
it is furnished with powerful fleshy trabeculæ.

The bulbus or conus arteriosus is prolonged into the branchial artery
which soon divides, sending off a branch to each branchial arch. On
returning from the respiratory organ the branchial veins assume the
structure and functions of arteries. Several branches are sent off
to different portions of the head and to the heart, but the main
trunks unite to form the great artery which carries the blood to the
viscera and all the parts of the trunk and tail, and which, therefore,
represents the _aorta_ of higher animals.

In the majority of Teleosteans the _aorta_ has proper walls formed
by its own membranes, but in the Sturgeons it is independent at its
commencement only, and replaced by a canal formed by hæmal elements of
the vertebral column, and clothed inside with a perichondrium. In many
Chondropterygians and some Teleosteans (_Esox_, _Clupea_, _Silurus_),
the aorta possesses its own firm membranes along its ventral side,
dorsally being protected by a very thin membrane only, attached to the
concavity of the centra of the vertebræ.

The circulatory system of _Branchiostoma_ and of the _Dipnoi_ shows
essential differences from that of other fishes.

_Branchiostoma_ is the only fish which does not possess a muscular
heart, several cardinal portions of its vascular system being
contractile. A great vein extends forwards along the caudal region
below the notochord, and exhibits contractility in a forward direction;
it is bent anteriorly, passing into another tube-like pulsatile trunk,
the branchial heart, which runs along the middle of the base of the
pharynx, sending off branches on each side to the branchiæ; each of
these branches has a small contractile dilatation (_bulbillus_) at
its base. The two anterior branches pass directly into the aorta, the
others are branchial arteries, the blood of which returns by branchial
veins emptying into the aorta. The blood of the intestinal veins is
collected in a contractile tube, the portal vein, situated below the
intestine, and distributed over the rudimentary liver. Of all other
fishes, only in _Myxinoids_ the portal vein is contractile. All the
blood-corpuscles of _Branchiostoma_ are colourless and without nucleus.

In _Dipnoi_ a rudimentary division of the heart into a right and
left partition has been observed; this is limited to the ventricle
in _Ceratodus_, but in _Lepidosiren_ and _Protopterus_ an incomplete
septum has been observed in the atrium also. All Dipnoi have a pulmonal
vein, which enters the atrium by a separate opening, provided with a
valve. The pulmonal artery rises in _Lepidosiren_ and _Protopterus_
from an arch of the aorta, but in _Ceratodus_ it is merely a
subordinate branch, rising from the _Arteria cœliaca_.




                              CHAPTER XI.

                            URINARY ORGANS.


In _Branchiostoma_ no urinary organs have been found.

In Myxinoids these organs are of a very primitive structure: they
consist of a pair of ducts, extending from the urogenital porus through
the abdominal cavity. Each duct sends off at regular intervals from
its outer side a short wide branch (the uriniferous tube), which
communicates by a narrow opening with a blind sac. At the bottom of
this sac there is a small vaso-ganglion (_Malpighian corpuscle_),
by which the urine is secreted.

In the Lampreys the kidneys form a continuous gland-like body, with
irregular detached small portions. The ureters coalesce before they
terminate in the urogenital papilla.

In Chondropterygians the kidneys occupy the posterior half or
two-thirds of the back of the abdominal cavity, without the sac of the
peritoneum (as in all fishes) which forms a firm tendinous horizontal
septum. The kidneys of the two sides are never confluent, and generally
show a convoluted or lobulated surface. The ureters are short; each is
dilated into a pouch, and communicating with its fellow terminates by a
single urethra (which also receives the vasa deferentia) behind the end
of the rectum in the large common cloaca.

In Ganoids the kidneys occupy a similar position as in
Chondropterygians, but these fishes differ considerably with regard
to the termination and the arrangement of the ends of the urogenital
ducts. The Dipnoi possess a cloaca. In _Ceratodus_ the ureters
open into it by a common opening, separate from the genital opening;
and no closed urinary bladder has been developed. _Lepidosiren_
has a small urinary bladder; the ureters do not communicate directly
with it, but terminate separately on small papillæ in the dorsal
compartment of the cloaca. The other Ganoids lack a cloaca, and the
urogenital opening is behind the vent as in Teleosteans. In all the
genital and urinary ducts coalesce towards their end. The Sturgeons
have no urinary bladder, whilst it is present in _Amia_, the
ureters opening separately into it.

The _kidneys_ of Teleosteans are situated likewise without the
peritoneal cavity, immediately below some part of the vertebral column,
and vary exceedingly with regard to form and extent. Sometimes they
reach from the skull to between the muscles of the tail, sometimes
they are limited to the foremost part of the abdominal cavity (in
advance of the diaphragm), but generally their extent corresponds to
that of the abdominal portion of the vertebral column. Frequently
they are irregular on their dorsal surface, filling every available
recess, flat, attenuated on the sides, more or less coalescent towards
the middle; in other fishes they are more compact bodies. The ureters
terminate, either separate or united, in a urinary bladder, varying
in shape, which opens by a short urethra behind the vent. The urinary
opening may be separate or confluent with that of the genital ducts,
and is frequently placed on a more or less prominent papilla (_papilla
urogenitalis_). If separate, the urinary opening is behind the genital;
and if a papilla is developed, its extremity is perforated by the
urethra, the genital opening being situated nearer the base. A few
Teleosteans show an arrangement similar to that of Chondropterygians
and Dipnoi, the urogenital openings being in the posterior wall of the
rectum (_Symbranchidæ_, _Pediculati_, and some _Plectognathi_).




                             CHAPTER XII.

                        ORGANS OF REPRODUCTION.


All fishes are _dioecious_, or of distinct sex. Instances of so-called
_hermaphroditism_ are, with the exception of _Serranus_, abnormal
individual peculiarities, and have been observed in the Cod-fish, some
Pleuronectidæ, and in the Herring. Either the generative organ of one
side was found to be male, that of the other female; or the organ of
one or both sides was observed to have been developed partly into an
ovary partly into a testicle. In the European species of Serranus a
testicle-like body is attached to the lower part of the ovary; but
many specimens of this genus are undoubtedly males, having normally
developed testicles only.

The majority of fishes are oviparous, comparatively few viviparous;
the embryos being developed either in the ovarium or in some dilated
portion of the oviduct. In viviparous fishes actual copulation takes
place, and the males of most of them are provided with copulatory
or intromittent organs. In oviparous fishes the generative products
are, during sexual excitement, discharged into the water, a very
small quantity of semen being sufficient for effectual impregnation
of a number of ova dispersed in a considerable quantity of water;
circumstances which render _artificial impregnation_ more practicable
than in any other class of animals.

In _Branchiostoma_ the generative organs occupy the ventral side of the
abdominal cavity, into which they discharge their contents. No ducts
are developed in either sex.

In the _Cyclostomes_ the generative organ is single, and fixed to or
suspended from the median line of the back of the visceral cavity
by a duplicature of the peritoneum (_mesoarium_); the testicle and
ovary being distinguishable by their contents only. These escape by
dehiscence of the cells or capsules and rupture of the peritoneal
covering into the abdominal cavity, and are expelled by reciprocal
pressure of the intertwined sexes through the _porus genitalis_, which
is sunk between two labia of the skin in _Myxine_, and produced into a
long papilla in Petromyzon.

  [Illustration: Fig. 69.--Ovum of Myxine glutinosa, enlarged.]

The ova of the Lampreys are small, globular, like those of Teleosteans.
Those of Myxine have a very peculiar shape when mature; they are of an
oval form, about 15 millimetres long and 8 millimetres broad, enveloped
in a horny case, which at each end is provided with a bundle of short
threads, each thread ending in a triple hook. Whilst in the mesoarial
fold the eggs are attached to one another by means of these hooks, and
after being expelled they probably fix themselves by the same means to
other objects. As in all fishes producing ova of large size, the number
of ova matured in one season is but small.

In _Teleosteans_ the generative organs are comparatively large. In
some families the ovaries are without closed covering and without
oviducts, as in _Salmonidæ_, _Galaxiidæ_, _Notopteridæ_, _Murænidæ_,
and others. The surface of such an open ovary--as, for instance, that
of the Salmon--is transversely plaited, the ova being developed in
capsules in the stroma of the laminæ; after rupture of the capsules
the mature ova drop into the abdominal cavity, and are expelled by
the porus genitalis. The ovaries of the other Teleosteans are closed
sacs, continued into oviducts. Frequently such ovaries coalesce into a
single body, or one in which the division is effected internally only
by a more or less complete septum. Fixed by a mesoarium, the ovaries
occupy generally a position outwards of the intestine or air-bladder;
their form varies as well as the thickness and firmness of their
covering, which frequently is an extremely thin transparent membrane.
The inner surface of the ovarian sac is transversely or longitudinally
plaited or covered with fringes, on which the ova are developed, as
in the open ovaries. In the viviparous Teleosteans the embryons are
likewise developed within the ovary, notably in the _Embiotocidæ_, many
_Blenniidæ_, and _Cyprinodontidæ_, _Sebastes viviparus_, etc. Among the
Cyprinodonts the end of the oviduct is attached to the anterior anal
rays, which are modified into supports of its termination. In _Rhodeus_
the oviduct is periodically prolonged into a long oviferous tube, by
means of which the female deposits her ova into the shells of living
Bivalves.

  [Illustration: Fig. 70.--Ditrema argenteum, with fully developed
  young, ready for expulsion by the genital orifice, _o_;
  _a_, folds of the ovarian sac; _v_, vent.]

The _ova_ of Teleosteous Fishes are extremely variable in size, quite
independently of the size of the parent species. The ova of large and
small individuals of the same species, of course, do not differ in
size; but, on the whole larger individuals produce a greater number
of ova than smaller ones of the same species. The larger the size of
the ova is in a species, the smaller is the number produced during
one season. The ova of the Eel are almost microscopic. The small
sized roe in the Herring, Lump-fish, Halibut, and Cod-fish, have been
estimated at respectively 25,000, 155,000, 3,500,000, and 9,344,000.
Larger in size and fewer in number are those of _Antennarius_, _Salmo_,
_Aspredo_, _Lophobranchs_, etc. Comparatively largest are those of
_Gastrosteus_; and the Siluroid genus _Arius_, the males of which
take care of their progeny, produces ova from 5 to 10 millimeters
in diameter. The ova of all Teleosteans are perfectly globular and
soft-shelled. Teleosteans without oviduct, deposit them separated from
one another; whilst in many Teleosteans with an oviduct the ova are
enveloped in a glutinous substance, secreted by its glands, swelling in
the water and forming lumps or cords, in which the ova are aggregated.

  [Illustration: Fig. 71. Ovum of Arius boakii (Ceylon), showing
  embryo. Nat. size.]

  [Illustration: Fig. 72.--Abdomen of _Aspredo batrachus_,
  with the ova attached; at _a_, the ova are removed, to show
  the spongy structure of the skin, and the processes filling the
  interspaces between the ova. (Natural size.)]

Instances of the female taking care of her progeny are extremely scarce
in fishes. At present only two examples are known, that of the Siluroid
genus _Aspredo_, and of _Solenostoma_. In the former, during the time
of propagation, the integuments of the lower side of the flat trunk of
the female assume a soft and spongy texture. After having deposited
the eggs, the female attaches them to, and presses them into, the
spongy integument, by merely lying over them. She carries them on her
belly, as the Surinam Toad (_Pipa_) carries her ova on the back. When
the eggs are hatched the excrescence on the skin disappears, and the
abdomen becomes as smooth as before. In _Solenostoma_ the inner side
of the long and broad ventral fins coalesces with the integuments of
the body, a large pouch being formed for the reception of the eggs.
There is a peculiar provision for the retention of the eggs in the
sac, and probably for the attachment of the embryo. The inner walls of
the sac are lined with long filaments, arranged in series along the
ventral rays, and more numerous and longer at the base of the rays than
in the middle of their length, behind which they disappear entirely.
They are also more developed in examples in which eggs are deposited
in the sac than in those which have the sac empty. The filaments most
developed have a length of half an inch, and are beset with mamilliform
appendages. A slightly undulated canal runs along the interior of the
filament.

  [Illustration: Fig. 73.--Solenostoma cyanopterum ♂ (Indian
  Ocean).]

  [Illustration: Fig. 74.--Pouch with ova, formed by the ventral
  fins of _Solenostoma_. Lower aspect; the edges of the fins
  have been pushed aside to allow of a view of the inside of the
  pouch. (Natural size.)]

The _Testicles_ of the _Teleosteans_ are always paired, and occupy the
same position as the ovaries. Their size varies extraordinarily at the
different seasons of the year. Vasa deferentia are constant. In the
males of viviparous Teleosteans the urogenital papilla is frequently
enlarged, and clearly serves as an intromittent organ. In _Clinus
despicillatus_ the vas deferens widens within the abdomen into a cavity
occupied by a complex network of loose fasciculi, rising from the
mucous membrane. The cavity can be compressed by a special powerful
muscle, the accumulated semen being thus expelled with considerable
force through the narrow aperture of the penis. In many Cyprinodonts
the vas deferens runs along the anterior anal rays, which may be
thickened, and prolonged into a long slender organ.

Many Teleostei take care of their progeny, but with the exception of
_Aspredo_ and _Solenostoma_, mentioned above (p. 160), it is the male
on which this duty devolves. In some, as in _Cottus_, _Gastrosteus_,
_Cyclopterus_, _Antennarius_, _Ophiocephalus_, _Callichthys_, the male
constructs with more or less skill a nest, and jealously guards the
ova deposited in it by the female. The male of some species of _Arius_
carries the ova (Fig. 71) about with him in his capacious pharynx.
The species of _Chromis_, inhabiting the sea of Galilee, are said
to take care of their ova in the same manner. And, finally, in the
Lophobranchs, nature has aided this instinct by the development of a
pouch on the abdomen or lower side of the tail. In the Syngnathidæ this
pouch is formed by a fold of the skin developed from each side of the
trunk and tail, the free margins of the fold being firmly united in the
median line, whilst the eggs are being hatched in the inside of the
pouch. In _Hippocampus_ the pouch is completely closed, with a narrow
anterior opening.

  [Illustration: Fig. 75.--Syngnathus acus ♂, with
  sub-caudal pouch.]

  [Illustration: Fig. 76.--Sub-caudal pouch of Syngnathus acus,
  with the young, ready to leave the pouch. One side of the
  membrane of the pouch is pushed aside to admit of a view of its
  interior. (Natural size.)]

The genital organs of _Ganoids_ show similar diversity of structure as
those of Teleosteans, but on the whole they approach the Batrachian
type. The ovaries are not closed, except in _Lepidosiren_; all
Ganoids possess oviducts. In the Sturgeons the oviduct as well as the
vas deferens is represented by a funnel-shaped prolongation of the
peritoneum, which communicates with the wide ureter. The inner aperture
of the funnel is on a level of the middle of the testicle or ovary,
the outer within the ureter; and it is a noteworthy fact that only at
certain periods of the life of the fish this outer aperture is found
to be open,--at other times the peritoneal funnel appears as a closed
blind sac within the ureter. The mode of passage of the semen into the
funnel is not known.

In _Polypterus_ and _Amia_, proper oviducts, with abdominal apertures
in about the middle of the abdominal cavity, are developed; they
coalesce with the ureters close to the common urogenital aperture.

In _Ceratodus_ (Fig. 77), a long convoluted oviduct extends to the
foremost limit of the abdominal cavity, where it opens by a slit at
a considerable distance from the front end of the long ovary; this
aperture is closed in sexually immature specimens. The oviducts unite
close to their common opening in the cloaca. During their passage
through the oviduct the ova receive a gelatinous covering secreted by
its mucous membrane. This is probably also the case in _Lepidosiren_,
which possesses a convoluted oviduct with secretory glands in the
middle of its length. The oviduct begins with a funnel-shaped
dilatation, and terminates in a wide pouch, which posteriorly
communicates with that of the other side, both opening by a common
aperture behind the urinary bladder.

The ova of Ganoids, as far as they are known at present, are small,
but enveloped in a gelatinous substance. In the Sturgeon have been
counted as many as 7,635,200. Those of _Lepidosteus_ seem to be the
largest, measuring 5 millimetres in diameter with their envelope, and 3
millimetres without it. They are deposited singly, like those of Newts.

  [Illustration: Fig. 77.--Ovaries of Ceratodus.

    _a_, Right ovary shown from the inner surface, which is
    covered by the peritoneum; _a’_, Left ovary, showing its
    outer surface; _l_, Portion of liver; _o_, Oviduct; _p_, the
    lower part of the oviduct is opened to show the folds of its
    inner membrane; _q_, Opening of the left oviduct into the
    right; _r_, Abdominal orifice of the oviduct.]

In _Chondropterygians_ (and _Holocephali_) the organs of reproduction
assume a more compact form, and are more free from a lengthened
attachment to the back of the abdominal cavity. The ovaries of the
majority are paired, single in the _Carchariidæ_ and _Scylliidæ_, one
remaining undeveloped. But the oviducts are always paired, beginning
immediately behind the diaphragma with a common aperture. They consist
of two divisions, separated by a circular valve; the upper is narrow,
and provided within its coats with a gland which secretes the leathery
envelope in which most of the Chondropterygian ova are enclosed; the
lower forms the uterine dilatation, in which the embryoes of the
viviparous species are developed. Generally the vitelline sac of the
embryoes is free, and without connection with the uterus, which in
these cases has merely the function of a protecting pouch; but in
Carcharias and Mustelus lævis a _placenta uterina_ is formed, the
vascular walls of the vitelline sac forming plaits fitting into those
of the membrane of the uterus. The ends of the uteri open by a common
aperture behind the ureter into the cloaca.

  [Illustration: Fig. 78.--Ventral fins and claspers of
  Chiloscyllium trispeculare.]

The testicles are always paired, rounded, and situated in the anterior
part of the abdominal cavity, covered by the liver. _Vasa efferentia_
pass the semen into a much-convoluted _epididymis_, which is continued
into the _vas deferens_; this, at the commencement of its course, is
spirally wound, but becomes straight behind, and has its end dilated
into a seminal reservoir. It opens with the urethra in a papilla within
the cloaca.

The so-called _claspers_ of Chondropterygians (Fig. 78) are
characteristic of all male individuals. They are semi-ossified
appendages of the pubic, with which they are movably joined, and
special muscles serve to regulate their movements. Sometimes they
are armed with hook-like osseous excrescences (_Selache_). They are
irregularly longitudinally convoluted, and, when closely ad-pressed to
each other, form a canal open at their extremity. A gland, abundantly
discharging a secretion during the season of propagation, is situated
at, and opens into, the base of the canal. It is still doubtful whether
the generally-adopted opinion that their function consists in holding
the female during copulation is correct, or whether they are not
rather an intromittent organ, the canal of which not only conducts the
secretion of their proper gland but also the impregnating fluid.

  [Illustration: Fig. 79.--Egg of a Scyllium from Magelhan’s
  Straits (? Sc. chilense). Natural size.]

  [Illustration: Fig. 80.--Egg-shell of Cestracion philippi, half
  natural size, linear.

  I. External view. II. Vertical section.

  _a_, One spiral ridge; _b_, The other spiral ridge;
  _c_, Cavity for the ovum.]

The ova of the oviparous Chondropterygians are large and few in number;
they are successively impregnated, and the impregnation must take
place before they are invested with a tough leathery envelope which
would be impenetrable to the semen, that is, before they enter the
uterus; therefore, copulation must take place in all these fishes. The
form of the egg-shell differs in the various genera; generally (Fig.
79) they are flattened, quadrangular, with each of the four corners
produced, and frequently prolonged into long filaments which serve for
the attachment of the ova to other fixed objects. In _Notidanus_ the
surfaces are crossed by numerous ridges. In _Cestracion_ (Fig. 80) the
egg is pyriform, with two broad ridges or plates, wound edgewise round
it, the two ridges forming five spires. The eggs of _Callorhynchus_
(Fig. 81) have received a protective resemblance to a broad-leaved
fucus, forming a long depressed ellipse, with a plicated and fringed
margin.

  [Illustration: Fig. 81.--Egg of Callorhynchus antarcticus.
  _a_, Cavity for the embryo.]




                             CHAPTER XIII.

                    GROWTH AND VARIATION OF FISHES.


Changes of form normally accompanying growth (after absorption of the
vitelline sac) are observed in all fishes; but in the majority they
affect only the proportional size of the various parts of the body. In
young fishes the eyes are constantly larger than in adult relatively
to the size of the head; and again, the head is larger relatively to
that of the body. Changes amounting to metamorphosis have been hitherto
observed in _Petromyzon_ only. In the larval condition (_Ammocætes_)
the head is very small, and the toothless buccal cavity is surrounded
by a semicircular upper lip. The eyes are extremely small, hidden in a
shallow groove; and the vertical fins form a continuous fringe. In the
course of three or four years the teeth are developed, and the mouth
changes into a perfect suctorial organ; the eyes grow; and the dorsal
fin is divided into two divisions. In Malacopterygians and Anacanths
the embryonal fringe from which the vertical fins are developed, is
much longer persistent than in Acanthopterygians. A metamorphosis
relating to the respiratory organs, as in Batrachians, is indicated in
the class of Fishes by the external gills with which fœtal Plagiostomes
(Fig. 58, p. 136) and the young of some Ganoids, viz. the _Protopterus_
and _Polypterus_, are provided.

  [Illustration: Fig. 82.--Mouth of Larva of Petromyzon
  branchialis.]

  [Illustration: Fig. 83.--Mouth of Petromyzon fluviatilis.

   _mx_, Maxillary tooth; _md_, Mandibulary tooth;
   _l_, Lingual tooth; _s_, Suctorial teeth.]

  [Illustration: Fig. 84.--Armature of præoperculum of young Caranx
  ferdau. (Magnified.)

  I. Of an individual, 1¼ inch long. II. Of an individual, 2 inches
  long.]

  [Illustration: Fig. 85.--Tholichthys osseus. Six times the
  natural size.]

  [Illustration: Fig. 86.--Tholichthys-stage of Heniochus (?).]

  [Illustration: Fig. 87.--Tholichthys-stage of Pomacanthus (magn.)
  Atlantic.]

  [Illustration: Fig. 88.--Young Chætodon citrinellus (30 mill.
  long).]

One of the most extraordinary changes by which, during growth, the
form and position of several important organs are affected, occurs
in Flat-fishes (_Pleuronectidæ_); their young are symmetrically
formed, with a symmetrical mouth, and with one eye on each side, and,
therefore, keep their body in a vertical position when swimming.
As they grow they live more on the bottom, and their body, during
rest, assumes a horizontal position; in consequence, the eye of the
lower side moves towards the upper, which alone is coloured; and in
many genera the mouth is twisted in the opposite direction, so that
the bones, muscles, and teeth are much more developed on the blind
side than on the coloured. In a great number of other _Teleostei_
certain bones of the head show a very different form in the young
state. Ossification proceeds in those bones in the direction of lines
or radii which project in the form of spines or processes; as the
interspaces between these processes are filled with bone, the processes
disappear entirely, or at least project much less in the older than
in the younger individuals (Fig. 84). The young of some fishes may be
armed with a long powerful præopercular or scapular spine, or show
a serrature of which nothing remains in the adult fish except some
ridges or radiating lines. These processes seem to serve as weapons
of defence during a period in the life of the fish in which it needs
them most. In not a few instances a portion of this armature is so
much developed that the disappearance of its most projecting parts
with the growth of the fish is not only due to its being surrounded
by other bone, but, partially at least, caused by absorption. The
_Carangidæ_, _Cyttidæ_, _Squamipinnes_, _Xiphiidæ_, offer instances
of such remarkable changes. A fish, described as _Tholichthys osseus_
(Fig. 85), is probably the young of a Cyttoid, the suprascapula,
humerus, and præoperculum forming enormously enlarged plates. In the
fish Fig. 86 those bones appear still enlarged, and the frontals
develop a remarkably long and curved horn above the orbit. In the
_Tholichthys_-stage of _Pomacanthus_ (specimens 10 millimetres long,
Fig. 87), the frontal bone is prolonged into a straight lancet-shaped
process, nearly half as long as the body; the suprascapular and
præopercular processes cover and hide the dorsal and ventral fins.
The plates attached to the shoulder-girdle remain persistent until
the young fish has assumed the form of the adult; thus they are still
visible in young _Chætodon citrinellus_, 30 millimetres long, in which
the specific characters are already fully developed.--The Sword-fishes
with ventral fins (_Histiophorus_) belong to the Teleosteans of the
largest size; in young individuals, 9 millimetres long (Fig. 89), both
jaws are produced, and armed with pointed teeth; the supraorbital
margin is ciliated; the parietal and præoperculum are prolonged
into long spines; the dorsal and anal fins are a low fringe, and
the ventrals make their appearance as a pair of short buds. When 14
millimetres long (Fig. 90) the young fish has still the same armature
of the head, but the dorsal fin has become much higher, and the
ventral filaments have grown to a great length. At a third stage, when
the fish has attained to a length of 60 millimetres, the upper jaw is
considerably prolonged beyond the lower, losing its teeth; the spines
of the head are shortened, and the fins assume nearly the shape which
they retain in mature individuals. Young Sword-fishes without ventral
fins (_Xiphias_) undergo similar changes; and, besides, their skin is
covered with small rough excrescences longitudinally arranged, which
continue to be visible after the young fish has assumed the form of the
mature in other respects (Fig. 92).

  [Illustration: Fig. 89.--Young Sword-fish (Histiophorus), 9 mill.
  long. Atlantic. (Magn.)]

  [Illustration: Fig. 90.--Young Sword-fish (Histiophorus), 14
  mill. long. South Atlantic. (Magn.)]

  [Illustration: Fig. 91.--Young Sword-fish (Histiophorus), 60
  mill. long. Mid-Atlantic.]

  [Illustration: Fig. 92.--Xiphias gladius, young, about 8 inches
  long.]

The Plectognaths show no less extraordinary changes: an extraordinary
form taken in the South Atlantic, and named _Ostracion boops_, is
considered by Lütken to be the young of a Sun-fish (_Orthagoriscus_).
In very young more advanced Sun-fishes (18 to 32 millimetres) the
vertical diameter of the body exceeds, or is not much less than, the
longitudinal; and small conical spines are scattered over its various
parts. The caudal fin is developed long after the other vertical fins.

  [Illustration: Fig. 93.--“Ostracion boops” (much magnified).]

  [Illustration: Fig. 94.--Young of Orthagoriscus, 18 and 32 mill.
  long. (Natural size.)]

Similar changes take place in a number of other fishes, and in
many cases the young are so different that they were described as
distinct genera: thus _Priacantichthys_ has proved to be the young of
_Serranus_, _Rhynchichthys_ that of _Holocentrum_, _Cephalacanthus_ of
_Dactylopterus_, _Dicrotus_ of _Thyrsites_, _Nauclerus_ of _Naucrates_,
_Porthmeus_ of _Chorinemus_, _Lampugus_ of _Coryphæna_, _Acronurus_
of _Acanthurus_, _Keris_ of _Naseus_, _Porobronchus_ of _Fierasfer_,
_Couchia_ of _Motella_, _Stomiasunculus_ of _Stomias_, etc.

The fins are most frequently subject to changes; but, whilst in some
fishes parts of them are prolonged into filaments with age, in others
the filaments exist during the early life-periods only; whilst in some
a part of the dorsal or the ventral fins is normally developed in the
young only, in others those very parts are peculiar to the mature age.
The integuments are similarly altered: in some species the young only
has asperities on the skin, in others the young are smooth and the old
have a tubercular skin; in some the young only have a hard bony head;
in others (some Siluroids) the osseous carapace of the head and neck,
as it appears in the adult, is more or less covered with soft skin
whilst the fish is young.

In not a few fishes the external changes are in relation to the sexual
development (_Callionymus_, many _Labyrinthici_, Cyprinodonts). These
_secondary sexual differences_ show themselves in the male individual,
only when it commences to enter upon his sexual functions, and it may
require two or more seasons before its external characteristics are
fully developed. Immature males do not differ externally from the old
female. The male secondary sexual characters consist principally in
the prolongation of some of the fin-rays, or of entire fins; and in
_Salmonidæ_ in the greater development of the jaw-bones. The coloration
of the male is in many fishes much brighter and more variegated than
that of the female, but in comparatively few permanent (as in some
_Callionymus_, _Labrus mixtus_); generally it is acquired immediately
before and during the season of propagation only, and lost afterwards.
Another periodical change in the integuments, also due to sexual
influence and peculiar to the male, is the excrescence of wart-like
tubercles on the skin of many _Cyprinoids_; they are developed chiefly
on the head, but sometimes extend over the whole body and all the fins.

With regard to size, it appears that in all Teleosteous fishes the
female is larger than the male; in many Cyprinodonts the male may be
only one-sixth or even less of the bulk of the female. The observations
on the relative size of the sexes are few in Palæichthyes, but such as
have been made tend to show that, if a difference exists at all, the
male is generally the larger (_Lepidosteus_). In the Rays (_Raja_) the
sexes, after they have attained maturity, differ in the development of
dermal spines and the form of the teeth, the female being frequently
much rougher than the male. There is much variation in this respect in
the different species; but the males are constantly distinguished by
an oblong patch of erectile claw-like spines on each pectoral fin, and
by having the teeth (all, or only a portion) pointed, and not obtuse,
like those of the females. In Sharks no secondary sexual differences
have been observed; the male _Chimæridæ_ (see Fig. 96, p. 184), possess
a singular comb-like cartilaginous appendage on the top of the head,
which can be erected or depressed into a groove, both the appendage and
the anterior part of the groove being armed with hooklets. The use of
this singular organ is not known.

The majority of Teleostei are _mixogamous_--that is, the males and
females congregate on the spawning-beds, and the number of the former
being in excess, several males attend to the same female, frequently
changing from one female to another. The same habit has been observed
in _Lepidosteus_. _Gastrosteus_ is truly polygamous, several females
depositing their ova into the same nest, guarded by one male only. Some
Teleostei (_Ophiocephalus_), and probably all Chondropterygians, are
monogamous; and it is asserted that the connection between the pair is
not merely temporary, but lasts until they are separated by accident.
Monogamous are probably also all those Teleosteans which bring forth
living young, and those, the males of which, for the attraction of
the female, are provided with appendages, or ornamented with a bright
coloration.

_Hybridism_ is another source of changes and variations within the
limits of a species, and is by no means so scarce as has been believed
hitherto; it is only apparently of exceptional occurrence, because
the life of fishes is more withdrawn from our direct observation than
that of terrestrial animals. It has been observed among species of
_Serranus_, _Pleuronectidæ_, _Cyprinidæ_, _Clupeidæ_, and especially
_Salmonidæ_. As in other animals, the more certain kinds of fishes
are brought under domestication, the more readily do they interbreed
with other allied species. It is characteristic of hybrids that their
characters are very variable, the degrees of affinity to one or the
other of the parents being inconstant; and as these hybrids are known
readily to breed with either of the parent race, the variations of
form, structure, and colour are infinite. Of internal organs the
dentition, gill-rakers, pyloric appendages, are those particularly
affected by such mixture of species.

       *       *       *       *       *

Some fishes are known to grow rapidly (in the course of from one to
three years) and regularly to a certain size, growth being definitely
arrested after the standard has been attained. Such fishes may be
called “full-grown,” in the sense in which the term is applied to
warm-blooded Vertebrates--the Sticklebacks, most Cyprinodonts, and many
Clupeoids (Herring, Sprat, Pilchard) are examples of this regular
kind of growth.[15] But in the majority of fishes the rate of growth
is extremely irregular, and it is hardly possible to know when growth
is actually and definitely arrested. All seems to depend on the amount
of food and the more or less favourable circumstances under which the
individual grows up. Fishes which rapidly grow to a definite size are
short-lived, whilst those which steadily and slowly increase in size
attain to a great age, Teleosteans as well as Chondropterygians. Carp
and Pike have been ascertained to live beyond a hundred years.

It is evident that such diversity and irregularity of growth in
the same species is accompanied by considerable differences in the
appearance and general development of the fish. No instance is more
remarkable than that of the so-called _Leptocephali_, which for a
long time have been regarded either as a distinct group of Fishes, or
as the larval stages of various genera of fishes.

  [Illustration: Fig. 95.--Leptocephalus.]

The _Leptocephali_ proper are small, narrow, elongate, more or less
band-shaped fishes, pellucid in a fresh state, but assuming a white
colour when preserved in spirits, resembling a tapeworm, being quite
as soft and flexible. The skeleton is entirely cartilaginous, or
slight ossifications are only now and then visible, especially towards
the end of the vertebral column. The latter is replaced by a chorda
dorsalis which, in many specimens, is found to be divided into numerous
segments. Neural arches are sometimes present in their rudimentary
condition. The anterior end of the chorda passes into the cartilaginous
base of the skull, the connection not being by means of joint and
ligaments. Hæmal arches are found on the caudal portion. Ribs none. The
skull, like the vertebral column, is nearly entirely cartilaginous.
The basisphenoid, frontal, and jaw-bones are the first which may be
distinguished, and the mandible has generally ossifications.

The muscles are generally not attached to the chorda, which is
surrounded by a thick gelatinous mass, separating the lateral sets of
muscles from each other. These muscles are attached to the external
integument, each forming a thin flat angular band, the angle being
directed forwards. However, specimens are frequently found in which the
muscles are more developed, evidently at the expense of the gelatinous
matter, which is diminished in quantity. They are attached to the
chorda, and the entire fish has a more cylindrical form of the body
(_Helmichthys_).

The nervous, circulatory, and respiratory organs are well developed.
In those with a sub-cylindrical body the blood is red, in those with
a flat body the blood-corpuscles show but rarely a faint coloration.
There are four branchial arches, and in some (_Tilurus_) pseudobrauchiæ
have been found. The gill-openings are more or less narrow. The
nostrils are double on each side, and the posterior is close to the eye.

The stomach has a large blind sac, and in _Leptocephalus_ two lateral
cæca. The intestine is straight, running close to the abdominal
profile, with a small appendix directed forward and a larger one
directed backwards. The vent is nearly always very small, and, in
preserved examples at least, cannot always be discovered. Its position
is variable, even in examples entirely similar in other points.
Air-bladder none. No trace of generative organs.

The vertical fins, when present, are confluent, with more or less
conspicuous traces of rays; sometimes they are merely a fold of the
skin, without any rays. Pectoral fins sometimes present, sometimes
rudimentary, sometimes entirely absent. Ventrals none.

Most examples have series of round black dots along each side of the
abdominal profile, along the lateral line, and sometimes along the
dorsal fin. They remind us of the luminous organs of many _Scopelidæ_,
_Stomiatidæ_, and other pelagic fishes, but are composed entirely of
pigmentary cells.

These fishes are found floating in the sea, frequently at a great
distance from land. Their movements are slow and languid. The largest
specimen of Leptocephalus observed was 10 inches, but specimens of that
size are very rare.

   [See Kölliker, Zeitschr. wiss. Zool. iv. 1852, p. 360; and
   Carus, Ueber die Leptocephaliden. Leipz. 1861. 4to.]

Taking into account all the various facts mentioned, we must come to
the conclusion that the Leptocephalids are the offspring of various
kinds of marine fishes, representing, not a normal stage of development
(larvæ), but an arrest of development at a very early period of their
life; they continue to grow to a certain size without corresponding
development of their internal organs, and perish without having
attained the characters of the perfect animal. The cause by which this
abnormal condition is brought about is not known; but it is quite
within the limits of probability that fishes usually spawning in the
vicinity of land sometimes spawn in the open ocean, or that floating
spawn is carried by currents to a great distance from land; and that
such embryoes, which for their normal growth require the conditions
afforded by the vicinity of the shore, if hatched in mid-ocean, grow
into undeveloped hydropic creatures, such as the Leptocephales seem to
be.

       *       *       *       *       *

Abundance or scarcity of food, and other circumstances connected with
the localities inhabited by fishes, affect considerably the colour of
their muscles and integuments; the periodical changes of colour in
connection with their sexual functions have been referred to above (p.
176). The flesh of many Teleostei is colourless, or but slightly tinged
by the blood; that of Scombridæ, most Ganoids and Chondropterygians,
is more or less red; but in badly-fed fishes, as well as in very
young ones, the flesh is invariably white (anæmic). Many fishes, like
the _Salmonidæ_, feed at times exclusively on Crustaceans, and the
colouring substance of these Invertebrates, which by boiling and by
the stomachic secretion turns red, seems to pass into the flesh of the
fishes, imparting to it the well-known “salmon” colour. Further, the
coloration of the integuments of many marine fish is dependent on the
nature of their surroundings. In those which habitually hide themselves
on the bottom, in sand, between stones or seaweeds, the colours of
the body readily assimilate to those of the vicinity, and are thus
an important element in the economy of their life. The changes from
one set or tinge of colours to another may be rapid and temporary, or
more or less permanent; in some fishes--as in the Pediculati, of which
the Sea-Devil, or _Lophius_, and _Antennarius_ are members--scarcely
two individuals are found exactly alike in coloration, and only
too frequently such differences in coloration are mistaken for
specific characters. The changes of colours are produced in two ways:
either by an increase or decrease of the black, red, yellow, etc.,
pigment-cells, or _chromatophors_, in the skin of the fish; or by the
rapid contraction or expansion of the chromatophors which happen to
be developed. The former change is gradual, like every kind of growth
or development; the latter rapid, owing to the great sensitiveness
of the cells, but certainly involuntary. In many bright-shining
fishes--as Mackerels, Mullets--the colours appear to be brightest in
the time intervening between the capture of the fish and its death: a
phenomenon clearly due to the pressure of the convulsively-contracted
muscles on the chromatophors. External irritation readily excites the
chromatophors to expand--a fact unconsciously utilised by fishermen,
who, by scaling the Red Mullet immediately before its death, produce
the desired intensity of the red colour of the skin, without which the
fish would not be saleable. However, it does not require such strong
measures to prove the sensitiveness of the chromatophors to external
irritation, the mere change of darkness into light is sufficient to
induce them to contract, the fish appearing paler, and _vice versa_. In
Trout which are kept or live in dark places, the black chromatophors
are expanded, and, consequently, such specimens are very dark-coloured;
when removed to the light they become paler almost instantaneously.

Total absence of chromatophors in the skin, or _Albinism_, is very rare
among fishes; much more common is _incipient Albinism_, in which the
dark chromatophors are changed into cells with a more or less intense
yellow pigment. Fishes in a state of domestication, like the Crucian
Carp of China, the Carp, Tench, and the Ide, are particularly subject
to this abnormal coloration, and are known as the common Gold-fish, the
Gold-Tench, and the Gold-Orfe. But it occurs also not rarely in fishes
living in a wild state, and has been observed in the Haddock, Flounder,
Plaice, Carp, Roach, and Eel.

It will be evident, from the foregoing remarks, that the amount of
variation within the limits of the same species--either due to the
natural growth and development, or to external physical conditions,
or to abnormal accidental circumstances--is greater in fishes than
in any of the higher classes of Vertebrates. The amount of variation
is greater in certain genera or families than in others, and it is
much greater in Teleosteans and Ganoids than in Chondropterygians.
Naturally, it is greatest in the few species which have been
domesticated, and which we shall mention in the succeeding chapter.

   [Illustration: Fig. 96.--Chimæra colliei ♂, west coast of
  North America. A. Front view of head. B. Palate. _a_, Peritoneal
  aperture; _b_, Nostrils; _c_, Vomerine teeth; _d_, Mandibular
  teeth; _e_, Palatine teeth; _f_, Claspers.]




                             CHAPTER XIV.

     DOMESTICATED AND ACCLIMATISED FISHES; ARTIFICIAL IMPREGNATION
           OF OVA--TENACITY OF LIFE AND REPRODUCTION OF LOST
           PARTS--HYBERNATION--USEFUL AND POISONOUS FISHES.


A few fishes only are thoroughly domesticated--that is, bred in
captivity, and capable of transportation within certain climatic
limits--viz. the Carp, Crucian Carp (European and Chinese varieties),
Tench, Orfe or Ide, and the Goramy. The two former have accompanied
civilised man almost to every place of the globe where he has effected
a permanent settlement.

Attempts to acclimatise particularly useful species in countries in
which they were not indigenous have been made from time to time, but
were permanently successful in a few instances only; the failures
being due partly to the choice of a species which did not yield the
profitable return expected, partly to the utter disregard of the
difference of the climatic and other physical conditions between the
original and new homes of the fish. The first successful attempts of
acclimatisation were made with domestic species, viz. the Carp and
Gold-fish, which were transferred from Eastern Asia to Europe. Then,
in the first third of the present century, the Javanese Goramy was
acclimatised in Mauritius and Guiana, but no care seems to have been
taken to insure permanent advantages from the successful execution
of the experiment. In these cases fully developed individuals were
transported to the country in which they were to be acclimatised. The
most successful attempt of recent years is the acclimatisation of the
Trout and Sea-Trout, and probably also of the Salmon, in Tasmania and
New Zealand, and of the Californian Salmon (_Salmo quinnat_?),
in Victoria, by means of artificially-impregnated ova. The ova were
transported on ice, in order to retard their development generally,
and thus to preserve them from destruction during the passage of the
tropical zone.

_Artificial impregnation_ of fish-ova was first practised by
J. L. JACOBI, a native of Westphalia, in the years 1757–63,
who employed exactly the same method which is followed now; and there
is no doubt that this able observer of nature conceived and carried
out his idea with the distinct object of advantageously restocking
water-courses which had become unproductive, and increasing production
by fecundating and preserving all ova, of which a great proportion,
in the ordinary course of propagation, would be left unfecundated
or accidentally perish. Physiology soon turned to account Jacobi’s
discovery, and artificial impregnation has proved to be one of the
greatest helps to the student of embryology.

Fishes differ in an extraordinary degree with regard to tenacity of
life. Some will bear suspension of respiration--caused by removal from
water, or by exposure to cold or heat--for a long time, whilst others
succumb at once. Nearly all marine fishes are very sensitive to changes
in the temperature of the water, and will not bear transportation from
one climate to another. This seems to be much less the case with some
freshwater fishes of the temperate zones: the Carp may survive after
being frozen in a solid block of ice, and will thrive in the southern
parts of the temperate zone. On the other hand, some freshwater
fishes are so sensitive to a change in the water that they perish
when transplanted from their native river into another apparently
offering the same physical conditions (Grayling, _Salmo hucho_).
Some marine fishes may be abruptly transferred from salt into fresh
water, like Sticklebacks, some Blennies, and _Cottus_, etc.;
others survive the change when gradually effected, as many migratory
fishes; whilst again, others cannot bear the least alteration in the
composition of the salt water (all pelagic fishes). On the whole,
instances of marine fishes voluntarily entering brackish or fresh water
are very numerous, whilst freshwater fishes proper but rarely descend
into salt water.

Abstinence from food affects different fishes in a similarly different
degree. Marine fishes can endure hunger less than freshwater fishes,
at least in the temperate zones, no observations having been made in
this respect on tropical fishes. Goldfishes, Carps, Eels, are known to
be able to subsist without food for months, without showing a visible
decrease of bulk; whilst the Trigloids, Sparoids, and other marine
fishes, survive abstinence from food for a few days only. In freshwater
fishes the temperature of the water is of great influence on their
vital functions generally, and consequently on their appetite,--many
cease to feed altogether in the course of the winter; a few, like the
Pike, are less inclined to feed during the heat of the summer than when
the temperature is lowered.

Captivity is easily borne by most fishes, and the appliances introduced
in our modern aquaria have rendered it possible to keep in confinement,
and even to induce to propagate, fishes which formerly were considered
to be intolerant of captivity.

Wounds affect fishes generally much less than higher Vertebrates. A
Greenland Shark continues to feed whilst his head is pierced by a
harpoon or by the knife, as long as the nervous centre is not touched;
a Sea-perch or a Pike (Fig. 97) will survive the loss of a portion of
its tail; a Carp that of half of its snout. However, some fishes are
much more sensitive, and perish even from the superficial abrasion
caused by the meshes of the net during capture (_Mullsn_.)

The power of _reproduction_ of _lost parts_ in Teleosteous fishes is
limited to the delicate terminations of their fin-rays and the various
tegumentary filaments with which some are provided. These filaments are
sometimes developed in an extraordinary degree, mimicking the waving
fronds of the seaweed in which the fish hides. Both the ends of the
fin-rays and the filaments are frequently lost, not only by accident,
but merely by wear and tear; and as these organs are essential for the
preservation of the fish, their reproduction is necessary.

  [Illustration: Fig. 97.--Pike caught in the Thames, which, when
  young, had lost part of the tail with the caudal fin.]

In Dipnoi, _Ceratodus_, and _Protopterus_, the terminal portion of the
tail has been found to have been reproduced, but without the notochord.

       *       *       *       *       *

_Hybernation_ has been observed in many Cyprinoids and Murænoids
of the temperate zones. They do not fall into a condition of complete
torpidity, as Reptiles and Mammals, but their vital functions are
simply lowered, and they hide in sheltered holes, and cease to go
abroad in search of their food. Between the tropics a great number
of fishes (especially Siluroids, Labyrinthici, Ophiocephaloids, the
Dipnoi), are known to survive long-continued droughts by passing the
dry season in a perfectly torpid state, imbedded in the hardened mud.
Protopterus, and probably many of the other fishes mentioned, prepare
for themselves a cavity large enough to hold them, and coated on the
inside with a layer of hardened mucus, which preserves them from
complete desiccation. It has been stated that in India fishes may
survive in this condition for more than one season, and that ponds
known to have been dry for several years, and to the depth of many
feet, have swarmed with fishes as soon as the accumulation of water
released them from their hardened bed.

       *       *       *       *       *

The principal _use_ derived by man from the class of Fishes consists in
the abundance of wholesome and nourishing food which they yield. In the
Polar regions especially, whole tribes are entirely dependent on this
class for subsistence; and in almost all nations fishes form a more or
less essential part of food, many being, in a preserved condition, most
important articles of trade. The use derived by man from them in other
respects is of but secondary importance. Cod-liver oil is prepared from
the liver of some of the Gadoids of the Northern Hemisphere, and of
Sharks; isinglass from the swim-bladder of Sturgeons, Sciænoids, and
Polynemoids; shagreen from the skin of Sharks and Rays.

       *       *       *       *       *

The flesh of some fishes is at times, or constantly, _poisonous_.
When eaten, it causes symptoms of more or less intense irritation of
the stomach and intestines, inflammation of the mucous membranes, and
not rarely death. The fishes, the flesh of which appears always to
have poisonous properties, are _Clupea thrissa_, _Clupea venenosa_,
and some species of _Scarus_, _Tetrodon_, and _Diodon_. There are
many others which have occasionally or frequently caused symptoms of
poisoning. Poey enumerates not less than seventy-two different kinds
from Cuba; and various species of _Sphyræna_, _Balistes_, _Ostracion_,
_Caranx_, _Lachnolæmus_, _Tetragonurus_, _Thynnus_, have been found
to be poisonous in all seas between the tropics. All or nearly all
these fishes acquire their poisonous properties from their food which
consists of poisonous Medusæ, Corals, or decomposing substances.
Frequently the fishes are found to be eatable if the head and
intestines be removed immediately after capture. In the West Indies it
has been ascertained that all the fishes living and feeding on certain
coral banks are poisonous. In other fishes the poisonous properties are
developed at certain seasons of the year only, especially the season of
propagation: as the Barbel, Pike, and Burbot, whose roe causes violent
diarrhœas when eaten during the season of spawning.

       *       *       *       *       *

  [Illustration: Fig. 98.--Portion of tail, with spines, of
  _Aëtobatis narinari_, a Sting-ray from the Indian Ocean.
  _a_, nat. size.]

_Poison-organs_ are more common in the class of Fishes than was
formerly believed, but they seem to have exclusively the function
of defence, and are not auxiliary in procuring food, as in venomous
Snakes. Such organs are found in the Sting-rays, the tail of which is
armed with one or more powerful barbed spines. Although they lack a
special organ secreting poison, or a canal in or on the spine by which
the venomous fluid is conducted, the symptoms caused by a wound from
the spine of a Sting-ray are such as cannot be accounted for merely by
the mechanical laceration, the pain being intense, and the subsequent
inflammation and swelling of the wounded part terminating not rarely
in gangrene. The mucus secreted from the surface of the fish and
inoculated by the jagged spine evidently possesses venomous properties.
This is also the case in many Scorpænoids, and in the Weaver
(_Trachinis_), in which the dorsal and opercular spines have the
same function as the caudal spines of the Sting-rays; however, in the
Weavers the spines are deeply grooved, the groove being charged with a
fluid mucus. In _Synanceia_ the poison-organ (Fig. 99,) is still
more developed: each dorsal spine is in its terminal half provided
with a deep groove on each side, at the lower end of which lies a
pear-shaped bag containing the milky poison; it is prolonged into a
membranous duct, lying in the groove of the spine, and open at its
point. The native fishermen, well acquainted with the dangerous nature
of these fishes, carefully avoid handling them; but it often happens
that persons wading with naked feet in the sea, step upon the fish,
which generally lies hidden in the sand. One or more of the erected
spines penetrate the skin, and the poison is injected into the wound by
the pressure of the foot on the poison-bags. Death has not rarely been
the result.

  [Illustration: Fig. 99.--A dorsal spine, with poison-bags, of
  _Synanceia verrucosa_. Indian Ocean.]

  [Illustration: Fig. 100.--Opercular part of the Poison-apparatus
  of _Thalassophryne_ (Panama).

  1. Hinder half of the head, with the venom-sac* _in situ._
  _a_, Lateral line and its branches; _b_, Gill-opening;
  _c_, Ventral fin; _d_, Base of Pectoral fin; _e_,
  Base of dorsal.

  2. Operculum with the perforated spine.]

The most perfect poison-organs hitherto discovered in fishes are those
of _Thalassophryne_, a Batrachoid genus of fishes from the coasts of
Central America. In these fishes the operculum again and the two dorsal
spines are the weapons. The former (Fig. 100, ^2) is very narrow,
vertically styliform and very mobile; it is armed behind with a spine,
eight lines long, and of the same form as the hollow venom-fang of
a snake, being perforated at its base and at its extremity. A sac
covering the base of the spine discharges its contents through the
apertures and the canal in the interior of the spine. The structure of
the dorsal spines is similar. There are no secretory glands imbedded
in the membranes of the sacs; and the fluid must be secreted by their
mucous membrane. The sacs are without an external muscular layer, and
situated immediately below the thick loose skin which envelops the
spines to their extremity; the ejection of the poison into a living
animal, therefore, can only be effected, as in _Synanceia_, by the
pressure to which the sac is subjected the moment the spine enters
another body.

Finally, a singular apparatus found in many Siluroids may be mentioned
in connection with the poison-organs, although its function is still
problematical. Some of these fishes are armed with powerful pectoral
spines and justly feared on account of the dangerous wounds they
inflict; not a few of them possess, in addition to the pectoral spines,
a sac with a more or less wide opening in the axil of the pectoral fin;
and it does not seem improbable that it contains a fluid which may be
introduced into a wound by means of the pectoral spine, which would
be covered with it, like the barbed arrow-head of an Indian. However,
whether this secretion is equally poisonous in all the species provided
with that axillary sac, or whether it has poisonous qualities at all,
is a question which can be decided by experiments only made with the
living fishes.




                              CHAPTER XV.

                    DISTRIBUTION OF FISHES IN TIME.


Of what kind the fishes were which were the first to make their
appearance on the globe; whether or not they were identical with,
or similar to, any of the principal types existing at present; are
questions which probably will for ever remain hidden in mystery and
uncertainty. The supposition that the Leptocardii and Cyclostomes,
the lowest of the vertebrate series, must have preceded the other
sub-classes, is an idea which has been held by many Zoologists: and
as the horny teeth of the Cyclostomes are the only parts of their
body which under favourable circumstances might have been preserved,
Palæontologists have ever been searching for this evidence.

  [Illustration: Fig. 101. Right dental plate of Myxine affinis.]

Indeed, in deposits belonging to the Lower Silurian and Devonian, in
Russia, England, and North America, minute, slender, pointed horny
bodies, bent like a hook, with sharp opposite margins, have been found
and described under the name of _Conodonts_. More frequently they
possess an elongated basal portion, in which there is generally a
larger tooth with rows of similar but smaller denticles on one or both
sides of the larger tooth, according as this is central or at one end
of the base. In other examples there is no prominent central tooth,
but a series of more or less similar teeth is implanted on a straight
or curved base. Modifications of these arrangements are very numerous,
and many Palæontologists entertain still doubts whether the origin
of these remains is not rather from Annelids and Mollusks than from
Fishes.

   [See G. J. Hinde, in “Quarterly Journal of the Geological
   Society,” 1879.]

The first undeniable evidence of a fish, or, indeed, of a vertebrate
animal, occurs in the _Upper Silurian_ Rocks, in a bone-bed of the
Downton sandstone, near Ludlow. It consists of compressed, slightly
curved, ribbed spines, of less than two inches in length (_Onchus_); of
small shagreen-scales (_Thelodus_); the fragment of a jaw-like bar with
pluricuspid teeth (_Plectrodus_); the cephalic bucklers of what seems
to be a species of _Pteraspis_; and, finally, the coprolitic bodies
of phosphate and carbonate of lime, including recognisable remains of
the Mollusks and Crinoids inhabiting the same waters. But no vertebra
or other part of the skeleton has been found. The spines and scales
seem to have belonged to the same kind of fish, which probably was a
Plagiostome. It is quite uncertain whether or not the jaw (if it be the
jaw of a fish[16]) belonged to the buckler-bearing _Pteraspis_, the
position of which among Ganoids, with which it is generally associated,
is open to doubt.

No detached undoubted tooth of a Plagiostome or Ganoid scale has been
discovered in the Ludlow deposits: but so much is certain that those
earliest remains in Palæozoic rocks belonged to fishes closely allied
to forms occurring in greater abundance in the succeeding formation,
the Devonian, where they are associated with undoubted Palæichthyes,
Plagiostomes as well as Ganoids.

       *       *       *       *       *

These fish-remains of the _Devonian_ or _Old Red Sandstone_, can be
determined with greater certainty. They consist of spines or the
so-called _Ichthyodorulites_, which show sufficiently distinctive
characters to be referred to several genera, one of them, _Onchus_,
still surviving from the Silurian epoch. All these spines are believed
to be those of Chondropterygians, to which order some pluricuspid
teeth (_Cladodus_) from the Old Red Sandstone in the vicinity of St.
Petersburg have been referred likewise.

The remains of the Ganoid fishes are in a much more perfect state of
preservation, so that it is even possible to obtain a tolerably certain
idea of the general appearance and habits of some of them, especially
of such as were provided with hard carapaces, solid scales, and
ordinary or bony fin-rays. A certain proportion of them, as might have
been expected, remind us, with regard to external form, of Teleosteous
fishes rather than of any of the few still existing Ganoid types; but
it is contrary to all analogy and to all palæontological evidence
to suppose that those fishes were, with regard to their internal
structure, more nearly allied to Teleosteans than to Ganoids. If they
were not true Ganoids, they may be justly supposed to have had the
essential characters of Palæichthyes. Other forms exhibit even at that
remote geological epoch so unmistakably the characteristics of existing
Ganoids, that no one can entertain any doubt with regard to their place
in the system. In none of these fishes is there any trace of vertebral
segmentation.

The Palæichthyes of the Old Red Sandstone, the systematic position
of which is still obscure, are the _Cephalaspidæ_ from the Lower Old
Red Sandstone of Great Britain and Eastern Canada; _Pterichthys_,
_Coccosteus_, and _Dinichthys_: genera which have been combined in
one group--_Placodermi_; and _Acanthodes_ and allied genera, which
combined numerous branchiostegals with chondropterygian spines and a
shagreen-like dermal covering.

Among the other Devonian fishes (and they formed the majority) two
types may be recognised, both of which are unmistakably Ganoids. The
first approaches the still living _Polypterus_, with which some of the
genera like _Diplopterus_ singularly agree in the form and armature of
the head, the lepidosis of the body, the lobate pectoral fins, and the
termination of the vertebral column. Other genera, as _Holoptychius_,
have cycloid scales; many have two dorsal fins (_Holoptychius_), and,
instead of branchiostegals, jugular scutes; others one long dorsal
confluent with the caudal (_Phaneropleuron_).

In the second type the principal characters of the _Dipnoi_ are
manifest, and some of them, for example _Dipterus_, _Palædaphus_,
_Holodus_, approach so closely the Dipnoi which still survive, that the
differences existing between them warrant a separation into families
only.

Devonian fishes are frequently found under peculiar circumstances,
enclosed in the so-called _nodules_. These bodies are elliptical
flattened pebbles, which have resisted the action of water in
consequence of their greater hardness, whilst the surrounding rock has
been reduced to detritus by that agency. Their greater density is due
to the dispersion in their substance of the fat of the animal which
decomposed in them. Frequently, on cleaving one of these nodules with
the stroke of the hammer, a fish is found embedded in the centre. At
certain localities of the Devonian, fossil fishes are so abundant
that the whole of the stratum is affected by the decomposing remains
emitting a peculiar smell when newly opened, and acquiring a density
and durability not possessed by strata without fishes. The flagstones
of Caithness are a remarkable instance of this.

       *       *       *       *       *

The fish-remains of the _Carboniferous_ formation show a great
similarity to those of the preceding. They occur throughout the series,
but are very irregularly distributed, being extremely scarce in some
countries, whilst in others entire beds (the so-called bone-beds) are
composed of ichthyolites. In the ironstones they frequently form the
nuclei of nodules, as in the Devonian.

Of Chondropterygians the spines of _Onchus_ and others still occur,
with the addition of teeth indicative of the existence of fishes
allied to the Cestracion-type (_Cochliodus_, _Psammodus_): a type
which henceforth plays an important part in the composition of the
extinct marine fish faunæ. Another extinct Selachian family, that of
Hybodontes, makes its appearance, but is known from the teeth only.

Of the Ganoid fishes, the family _Palæoniscidæ_ (Traquair) is
numerously represented; others are Cœlacanths (_Cœlocanthus_,
_Rhizodus_), and _Saurodipteridæ_ (_Megalichthys_). None of these
fishes have an ossified vertebral column, but in some (_Megalichthys_)
the outer surface of the vertebræ is ossified into a ring; the
termination of their tail is heterocercal. The carboniferous _Uronemus_
and the Devonian _Phaneropleuron_ are probably generically the same;
and the Devonian _Dipnoi_ are continued as, and well represented by,
_Ctenodus_.

       *       *       *       *       *

The fishes of the _Permian_ group are very similar to those of the
Carboniferous. A type which in the latter was but very scantily
represented, namely the _Platysomidæ_, is much developed. They were
deep-bodied fish, covered with hard rhomboid scales possessing a strong
anterior rib, and provided with a heterocercal caudal, long dorsal and
anal, short non-lobate paired fins (when present), and branchiostegals.
The _Palæoniscidæ_ are represented by many species of _Palæoniscus_,
_Pygopterus_ and _Acrolepis_, and Cestracionts by _Janassa_ and
_Strophodus_.

       *       *       *       *       *

The passage from the Palæozoic into the _Mesozoic_ era is not
indicated by any marked change as far as fishes are concerned. The
more remarkable forms of the Trias are Shark-like fishes represented
by ichthyodorulithes like _Nemacanthus_, _Liacanthus_, and _Hybodus_;
and Cestracionts represented by species of _Acrodus_ and _Strophodus_.
Of the Ganoid genera _Cœlacanthus_, _Amblypterus_ (_Palæoniscidæ_),
_Saurichthys_ persist from the Carboniferous epoch. _Ceratodus_ appears
for the first time (Muschel-Kalk of Germany).

Thanks to the researches of Agassiz, and especially Sir P. Egerton,
the ichthyological fauna of the Lias is, perhaps, the best known of
the Mesozoic era, 152 species having been described. Of the various
localities, Lyme Regis has yielded more than any other, nearly
all the Liassic genera being represented there by not less than
seventy-nine species. The Hybodonts and Cestracionts continue in
their fullest development. Holocephales (_Ischyodus_), true Sharks
(_Palæoscyllium_), Rays (_Squaloraja_, _Arthropterus_), and Sturgeons
(_Chondrosteus_) make their first appearance; but they are sufficiently
distinct from living types to be classed in separate genera, or even
families. The Ganoids, especially Lepidosteoids, predominate over
all the other fishes: _Lepidotus_, _Semionotus_, _Pholidophorus_,
_Pachycormus_, _Eugnathus_, _Tetragonolepis_, are represented by
numerous species; other remarkable genera are _Aspidorhynchus_,
_Belonostomus_, _Saurostomus_, _Sauropsis_, _Thrissonotus_, _Conodus_,
_Ptycholepis_, _Endactis_, _Centrolepis_, _Legnonotus_, _Oxygnathus_,
_Heterolepidotus_, _Isocolum_, _Osteorhachis_, _Mesodon_. These genera
offer evidence of a great change since the preceding period, the
majority not being represented in older strata, whilst, on the other
hand, many are continued into the succeeding oolithic formations. The
homocercal termination of the vertebral column commences to supersede
the heterocercal, and many of the genera have well ossified and
distinctly segmented spinal columns. Also the cycloid form of scales
becomes more common: one genus (_Leptolepis_) being, with regard to
the preserved hard portions of its organisation, so similar to the
Teleosteous type that some Palæontologists refer it (with much reason)
to that sub-class.

   [See _E. Sauvage_, Essai sur la Faune Ichthyologique de la
   période Liasique. In “Bibl. de l’école des hautes études,” xiii.
   art. 5. Paris 1875. 8^o.]

As already mentioned, the _Oolithic_ formations show a great similarity
of their fish-fauna to that of the Lias; but still more apparent is
its approach to the existing fauna. Teeth have been found which cannot
even generically be distinguished from _Notidanus_. The Rays are
represented by genera like _Spathobatis_, _Belemnobatis_, _Thaumas_;
the _Holocephali_ are more numerous than in the Lias (_Ischyodus_,
_Ganodus_). The most common Ganoid genera are _Caturus_, _Pycnodus_,
_Pholidophorus_, _Lepidotus_, _Leptolepis_, all of which had been more
or less fully represented in the Lias. Also _Ceratodus_ is continued
into it.

       *       *       *       *       *

The _Cretaceous_ group offers clear evidence of the further advance
towards the existing fauna. Teeth of Sharks of existing genera
_Carcharias_ (_Corax_), _Scyllium_, _Notidanus_, and _Galeocerdo_, are
common in some of the marine strata, whilst Hybodonts and Cestracionts
are represented by a small number of species only; of the latter one
new genus, _Ptychodus_, appears and disappears. A very characteristic
Ganoid genus, _Macropoma_, comprises homocercal fishes with rounded
ganoid scales sculptured externally and pierced by prominent mucous
tubes. _Caturus_ becomes extinct. Teeth and scales of _Lepidotus_
(with _Sphærodus_ as subgenus), clearly a freshwater fish, are widely
distributed in the Wealden, and finally disappear in the chalk; its
body was covered with large rhomboidal ganoid scales. _Gyrodus_
and _Aspidorhynchus_ occur in the beds of Voirons, _Coelodus_ and
_Amiopsis_ (allied to Amra), in those of Comen, in Istria. But the
Palæichthyes are now in the minority; undoubted Teleosteans have
appeared, for the first time, on the stage of life in numerous genera,
many of which are identical with still existing fishes. The majority
are Acanthopterygians, but Physostomes and Plectognaths are likewise
well represented, most of them being marine. Of Acanthopterygian
families the first to appear are the _Berycidæ_, represented by
several very distinct genera: _Beryx_; _Pseudoberyx_ with abdominal
ventral fins; _Berycopsis_ with cycloid scales; _Homonotus_,
_Stenostoma_, _Sphenocephalus_, _Acanus_, _Hoplopteryx_, _Platycornus_
with granular scales; _Podocys_ with a dorsal extending to the neck;
_Acrogaster_, _Macrolepis_, _Rhacolepis_ from the chalk of Brazil.
The position of _Pycnosterynx_ is uncertain, it approaches certain
Pharyngognaths. True _Percidæ_ are absent, whilst the _Carangidæ_,
_Sphyrænidæ_, _Cataphracti_, _Gobiidæ_, _Cottidæ_, and _Sparidæ_
are represented by one or more genera. Somewhat less diversified
are the Physostomes, which belong principally to the _Clupeidæ_ and
_Dercetidæ_, most of the genera being extinct; Clupea is abundant in
some localities. _Scopelidæ_ (_Hemisaurida_ and _Saurocephalus_) occur
in the chalk of Comen in Istria, and of Mæstricht. Of all cretaceous
deposits none surpass those of the Lebanon with regard to the number of
genera, species, and individuals; the forms are exclusively marine, and
the remains in the most perfect condition.

       *       *       *       *       *

In the _Tertiary_ epoch the Teleosteans have almost entirely replaced
the Ganoids; a few species only of the latter make their appearance,
and they belong to existing genera, or, at least, very closely
allied forms (_Lepidosteus_, _Amia_, _Hypamia_, _Acipenser_). The
Chondropterygians merge more and more into recent forms; Holocephali
continue, and still are better represented than in the present fauna.
The Teleosteans show even in the Eocene a large proportion of existing
genera, and the fauna of some localities of the Miocene (Oeningen)
is almost wholly composed of them. On the whole, hitherto more than
one-half have been found to belong to existing genera, and there is
no doubt that the number of seemingly distinct extinct genera will be
lessened as the fossils will be examined with a better knowledge of
the living forms. The distribution of the fishes differed widely from
that of our period, many of our tropical genera occurring in localities
which are now included within our temperate zone, and being mixed with
others, which nowadays are restricted to a colder climate: a mixture
which continues throughout the Pliocene.

       *       *       *       *       *

A few families of fishes, like the freshwater Salmonidæ, seem to have
put in their appearance in _Post-pliocene_ times; however, not much
attention has been paid to fish-remains of these deposits; and such as
have been incidentally examined offer evidence of the fact that the
distribution of fishes has not undergone any further essential change
down to the present period.

   [See _E. Sauvage_, Mémoire sur la Faune Ichthyologique de
   la période Tertiaire. Paris 1873. 8°.]

  [Illustration: Fig. 102.--_Pycnodus rhombus_, a Ganoid from
  the Upper Oolite.]




                             CHAPTER XVI.

         THE DISTRIBUTION OF EXISTING FISHES OVER THE EARTH’S
                       SURFACE--GENERAL REMARKS.


In an account of the geographical distribution of fishes the
_Freshwater_ forms are to be kept separate from the _Marine_. However,
when we attempt to draw a line between these two kinds of fishes, we
meet with a great number of species and of facts which would seem to
render that distinction very vague. There are not only species which
can gradually accommodate themselves to a sojourn in either salt or
fresh water, but there are also such as seem to be quite indifferent to
a rapid change from one into the other: so that individuals of one and
the same species (Gastrosteus, Gobius, Blennius, Osmerus, Retropinna,
Clupea, Syngnathus, etc.), may be found at some distance out at sea,
whilst others live in rivers far beyond the influence of the tide, or
even in inland fresh waters without outlet to the sea. The majority of
these fishes belong to forms of the fauna of the _brackish_ water, and
as they are not an insignificant portion of the fauna of almost every
coast, we shall have to treat of them in a separate chapter.

Almost every large river offers instances of truly marine fishes (such
as _Serranus_, _Sciænidæ_, _Pleuronectes_, _Clupeidæ_, _Tetrodon_,
_Carcharias_, _Trygonidæ_), ascending for hundreds of miles of their
course; and not periodically, or from any apparent physiological
necessity, but sporadically throughout the year, just like the
various kinds of marine Porpoises which are found all along the
lower course of the Ganges, Yang-tseKiang, the Amazons, the Congo,
etc. This is evidently the commencement of a change in a fish’s
habits, and, indeed, not a few of such fishes have actually taken up
their permanent residence in fresh waters (as species of Ambassis,
Apogon Dules, Therapon, Sciæna, Blennius, Gobius, Atherina, Mugil,
Myxus, Hemirhamphus, Clupea, Anguilla, Tetrodon, Trygon): all forms
_originally marine_.

On the other hand, we find fishes belonging to freshwater genera
descending rivers and sojourning in the sea for a more or less limited
period; but these instances are much less in number than those in which
the reverse obtains. We may mention species of _Salmo_ (the Common
Trout, the Northern Charr), and Siluroids (as _Arius_, _Plotosus_).
_Coregonus_, a genus so characteristic of the inland lakes of Europe,
Northern Asia, and North America, nevertheless offers some instances
of species wandering by the effluents into the sea, and taking up
their residence in salt water, apparently by preference, as _Coregonus
oxyrhynchus_. But of all the Freshwater families none exhibit so great
a capability of surviving the change from fresh into salt water, as
the _Gastrosteidæ_ (Sticklebacks), of the northern Hemisphere, and the
equally diminutive _Cyprinodontidæ_ of the tropics; not only do they
enter into, and live freely in, the sea, but many species of the latter
family inhabit inland waters, which, not having an outlet, have become
briny, or impregnated with a larger proportion of salts than pure sea
water. During the voyage of the “Challenger” a species of _Fundulus_,
_F. nigrofasciatus_, which inhabits the fresh and brackish waters of
the Atlantic States of North America, was obtained, with Scopelids and
other pelagic forms, in the tow-net, midway between St. Thomas and
Teneriffe.

Some fishes annually or periodically ascend rivers for the purpose of
spawning, passing the rest of the year in the sea, as Sturgeons, many
Salmonoids, some Clupeoids, Lampreys, etc. The two former evidently
belonged originally to the freshwater series, and it was only in the
course of their existence that they acquired the habit of descending
to the sea, perhaps because their freshwater home did not offer a
sufficient supply of food. These migrations of freshwater fishes have
been compared with the migrations of birds; but they are much more
limited in extent, and do not impart an additional element to the fauna
of the place to which they migrate, as is the case with the distant
countries to which birds migrate.

The distinction between freshwater and marine fishes is further
obscured by geological changes, in consequence of which the salt
water is gradually being changed into fresh, or _vice versa_. These
changes are so gradual and spread over so long a time, that many of
the fishes inhabiting such localities accommodate themselves to the
new conditions. One of the most remarkable and best studied instances
of such an alteration is the Baltic, which, during the second half
of the Glacial period, was in open and wide communication with the
Arctic Ocean, and evidently had the same marine fauna as the White
Sea. Since then, by the rising of the land of Northern Scandinavia
and Finland, this great gulf of the Arctic Ocean has become an inland
sea, with a narrow outlet into the North Sea, and its water, in
consequence of the excess of the fresh water pouring into it over the
loss by evaporation, has been so much diluted as to be nearly fresh
at its northern extremities: and yet nine species, the origin of
which from the Arctic Ocean can be proved, have survived the changes,
propagating their species, agreeing with their brethren in the Arctic
Ocean in every point, but remaining comparatively smaller. On the other
hand, fishes which we must regard as true freshwater fishes, like
the Rudd, Roach, Pike, Perch, enter freely the brackish water of the
Baltic.[17] Instances of marine fishes being permanently retained in
fresh water in consequence of geological changes are well known: thus
_Cottus quadricornis_ in the large lakes of Scandinavia; species of
_Gobius_, _Blennius_, and _Atherina_ in the lakes of Northern Italy;
_Comephorus_, of the depths of the Lake of Baikal, which seems to be
a dwarfed Gadoid. _Carcharias gangeticus_ in inland lakes of the Fiji
Islands, is another instance of a marine fish which has permanently
established itself in fresh water.

In the miocene formation of Licata in Sicily, in which fish remains
abound, numerous Cyprinoids are mixed with littoral and pelagic
forms. Sauvage found in 450 specimens from that locality, not less
than 266, which were Leucisci, Alburni, or Rhodei. Now, although it
is quite possible that in consequence of a sudden catastrophe the
bodies of those Cyprinoids were carried by a freshwater current into,
and deposited on the bottom of, the sea, the surmise that they lived
together with the littoral fishes in the brackish water of a large
estuary, which was not rarely entered by pelagic forms, is equally
admissible. And, if confirmed by other similar observations, this
instance of a mixture of forms which are now strictly freshwater or
marine, may have an important bearing on the question to what extent
fishes have in time changed their original habitat.

Thus there is a constant exchange of species in progress between the
freshwater and marine faunæ, and in not a few cases it would seem
almost arbitrary to refer a genus or even larger group of fishes
to one or the other; yet there are certain groups of fishes which
entirely, or with but few exceptions are, and, apparently, during
the whole period of their existence have been, inhabitants either of
the sea or of fresh water; and as the agencies operating upon the
distribution of marine fishes differ greatly from those influencing
the dispersal of freshwater fishes, the two series must be treated
separately. The most obvious fact that dry land, which intervenes
between river systems, offers to the rapid spreading of a freshwater
fish an obstacle which can be surmounted only exceptionally or by a
most circuitous route, whilst marine fishes may readily and voluntarily
extend their original limits, could be illustrated by a great number
of instances. Without entering into details, it may suffice to state
as the general result, that no species or genus of freshwater fishes
has anything like the immense range of the corresponding categories
of marine fishes; and that, with the exception of the Siluroids,
no other freshwater family is so widely spread as the families of
marine fishes. Surface temperature or climate which is, if not the
most, one of the most important physical factors in the limitation
of freshwater fishes, similarly affects the distribution of marine
fishes, but in a less degree, and only those which live near to the
shore or the surface of the ocean; whilst it ceases to exercise its
influence in proportion to the depth, the true deep-sea forms being
entirely exempt from its operation. Light, which is pretty equally
distributed over the localities inhabited by freshwater fishes, cannot
be considered as an important factor in their distribution, but it
contributes towards constituting the impassable barrier between the
surface and abyssal forms of marine fishes. Altitude has stamped the
fishes of the various Alpine provinces of the globe with a certain
character, and limited their distribution; but the number of these
Alpine forms is comparatively small, ichthyic life being extinguished
at great elevations even before the mean temperature equals that of the
high latitudes of the Arctic region, in which some freshwater fishes
flourish. On the other hand, the depths of the ocean, far exceeding the
altitude of the highest mountains, still swarm with forms specially
adapted for abyssal life. That other physical conditions of minor and
local importance, under which fresh water fishes live, and by which
their dispersal is regulated, are more complicated than similar ones
of the ocean, is probable, though perhaps less so than is generally
supposed: for the fact is that the former are more accessible to
observation than the latter, and are, therefore, more generally and
more readily comprehended and acknowledged. Thus, not only because many
of the most characteristic forms of the marine and freshwater series
are found, on taking a broader view of the subject, to be sufficiently
distinct, but also because their distribution depends on causes
different in their nature as well as the degree of their action, it
will be necessary to treat of the two series separately. Whether the
oceanic areas correspond in any way to the terrestrial will be seen in
the sequel.

  [Illustration: Fig. 103.--Ganoid scales of _Tetragonolepis_.]




                             CHAPTER XVII.

                THE DISTRIBUTION OF FRESHWATER FISHES.


Having shown above that numerous marine fishes enter fresh waters, and
that some of them have permanently established themselves therein,
we have to eliminate from the category of freshwater fishes all such
adventitious elements. They are derived from forms, the distribution
of which is regulated by other agencies, and which, therefore, would
obscure the relations of the faunæ of terrestrial regions if they were
included in them. They will be mentioned with greater propriety along
with the fishes constituting the fauna of the brackish water.

True freshwater fishes are the following families and groups only:--

    Dipnoi                with 4 species.
    Acipenseridæ and
      Polyodontidæ         „  26   „
    Amiidæ                 „   1   „
    Polypteridæ.           „   2   „
    Lepidosteidæ.          „   3   „
    Percina                „  46   „
    Grystina               „  11   „
    Aphredoderidæ          „   1   „
    Centrarchina           „  26   „
    Dules                  „  10   „
    Nandidæ                „   7   „
    Polycentridæ           „   3   „
    Labyrinthici           „  30   „
    Luciocephalidæ         „   1   „
    Gastrosteus            „  10   „
    Ophiocephalidæ         „  31   „
    Mastacembelidaæ        „  13   „
    Chromides              „ 105   „
    Comephoridæ            „   1   „
    Gadopsidæ              „   1   „
    Siluridæ               „ 572   „
    Characinidæ            „ 261   „
    Haplochitonidæ         „   3   „
    Salmonidæ (3 genera
      excepted)            „ 135   „
    Percopsidæ             „   1   „
    Galaxiidæ              „  15   „
    Mormyridæ (and
      Gymnarchidæ)         „  52   „
    Esocidæ                „   8   „
    Umbridæ                „   2   „
    Cyprinodontidæ         „ 112   „
    Heteropygii            „   2   „
    Cyprinidæ              „ 724   „
    Kneriidæ               „   2   „
    Hyodontidæ             „   1   „
    Osteoglossidæ          „   5   „
    Notopteridæ            „   5   „
    Gymnotidæ              „  20   „
    Symbranchidæ           „   5   „
    Petromyzontidæ         „  12   „
                           --------------
                     Total  2269 species.
                           ==============

As in every other class of animals, these freshwater genera and
families vary greatly with regard to the extent of their geographical
range; some extend over the greater half of the continental areas,
whilst others are limited to one continent only, or even to a very
small portion of it. As a general rule, a genus or family of freshwater
fishes is regularly dispersed and most developed within a certain
district, the species and individuals becoming scarcer towards the
periphery as the type recedes more from its central home, some outposts
being frequently pushed far beyond the outskirts of the area occupied
by it. But there are not wanting those remarkable instances of closely
allied forms occurring, almost isolated, at most distant points,
without being connected by allied species in the intervening space;
or of members of the same family, genus, or species inhabiting the
opposite shores of an ocean, and separated by many degrees of abyssal
depths. We mention of a multitude of such instances the following
only:--


_A_. Species identical in distant continents--

1. A number of species inhabiting Europe and the temperate parts of
eastern North America, as _Perca fluviatilis_, _Gastrosteus pungitius_,
_Lota vulgaris_, _Salmo solar_, _Esox lucius_, _Acipenser sturio_,
_Acipenser maculosus_, and several Petromyzonts.

2. _Lates calcarifer_ is common in India as well as in Queensland.

3. _Galaxias attenuatus_ inhabits Tasmania, New Zealand, the Falkland
Islands, and the southernmost part of the South American continent.

4. Several Petromyzonts enter the fresh waters of Tasmania, South
Australia, New Zealand, and Chili.


_B._ Genera identical in distant continents--

1. The genus _Umbra_, so peculiar a form as to be the type of a
distinct family consisting of two most closely allied species only, one
of which is found in the Atlantic States of North America, the other in
the system of the Danube.

2. A very distinct genus of Sturgeons, _Scaphirhynchus_, consisting
of two species only, one inhabiting fresh waters of Central Asia, the
other the system of the Mississippi.

3. A second most peculiar genus of Sturgeons, _Polyodon_, consists
likewise of two species only, one inhabiting the Mississippi, the other
the Yang-tse-kiang.

4. _Amiurus_, a Siluroid, and _Catostomus_, a Cyprinoid genus, both
well represented in North America, occur in a single species in
temperate China.

5. _Lepidosiren_ is represented by one species in tropical America, and
by the second in tropical Africa (_Protopterus_).

6. _Notopterus_ consists of three Indian and two West African species.

7. _Mastacembelus_ and _Ophiocephalus_, genera characteristic of the
Indian region, emerge severally by a single species in West and Central
Africa.

8. _Symbranchus_ has two Indian and one South American species.

9. _Prototroctes_, the singular antarctic analogue of _Coregonus_,
consists of two species, one in the south of Australia the other in New
Zealand.

10. _Galaxias_ is equally represented in Southern Australia, New
Zealand, and the southern parts of South America.


_C._ Families identical in distant continents--

1. The _Labyrinthici_, represented in Africa by 5, and in India by
25 species.

2. The _Chromides_, represented in Africa by 25, and in South
America by 80 species.

3. The _Characinidæ_, represented in Africa by 35, and in South
America by 226 species.

4. The _Haplochitonidæ_, represented in Southern Australia by one,
in New Zealand by one, and in Patagonia by a third species.

This list could be much increased from the families of _Siluridæ_
and _Cyprinidæ_, but as these have a greater range than the other
Freshwater fishes, they do not illustrate with equal force the object
for which the list has been composed.

       *       *       *       *       *

The ways in which the dispersal of Freshwater fishes has been effected
were various; they are probably all still in operation, but most work
so slowly and imperceptibly as to escape direct observation; perhaps,
they will be more conspicuous, after science and scientific inquiry
shall have reached to a somewhat greater age. From the great number
of freshwater forms which we see at this present day acclimatised in,
gradually acclimatising themselves in, or periodically or sporadically
migrating into, the sea, we must conclude that, under certain
circumstances, salt water may cease to be an impassable barrier at some
period of the existence of freshwater species, and that many of them
have passed from one river through salt water into another. Secondly,
the headwaters of some of the grandest rivers, the mouths of which are
at opposite ends of the continents which they drain, are sometimes
distant from each other a few miles only; the intervening space may
have been easily bridged over for the passage of fishes by a slight
geological change affecting the level of the watershed, or even by
temporary floods; and a communication of this kind, if existing for a
limited period only, would afford the ready means of an exchange of
a number of species previously peculiar to one or the other of those
river or lake systems. Some fishes, provided with gill-openings so
narrow that the water moistening the gills cannot readily evaporate;
and endowed, besides, with an extraordinary degree of vitality, like
many Siluroids (_Clarias_, _Callichthys_), Eels, etc., are enabled to
wander for some distance over land, and may thus reach a water-course
leading them thousands of miles from their original home. Finally,
fishes or their ova may be accidentally carried by waterspouts, by
aquatic birds or insects, to considerable distances.

Freshwater fishes of the present fauna were already in existence when
the great changes of the distribution of land and water took place
in the tertiary epoch; and having stated that salt water is not an
absolute barrier to the spreading of Freshwater fishes, we can now
more easily account for those instances of singular disconnection of
certain families or genera. It is not necessary to assume that there
was a continuity of land stretching from the present coast of Africa
to South America, or from South America to New Zealand and Australia,
to explain the presence of identical forms at so distant localities;
it suffices to assume that the distances were lessened by intervening
archipelagoes, or that an oscillation has taken place in the level of
the land area.

Dispersal of a type over several distant continental areas may be
evidence of its great antiquity, but it does not prove that it is of
greater antiquity than another limited to one region only. Geological
evidence is the only proof of the antiquity of a type. Thus, although
the _Dipnoi_ occur on the continents of Africa, South America, and
Australia, and their present distribution is evidently the consequence
of their wide range in palæozoic and secondary epochs; the proof
of their high antiquity can be found in their fossil remains only.
For, though the Siluroids have a still greater range, their wide
distribution is of comparatively recent date, as the few fossil remains
that have been found belong to the tertiary epoch. The rapidity of
dispersal of a type depends entirely on its facility to accommodate
itself to a variety of physical conditions, and on the degree of
vitality by which it is enabled to survive more or less sudden changes
under unfavourable conditions; proof of this is afforded by the family
of Siluroids, many of which can suspend for some time the energy of
their respiratory functions, and readily survive a change of water.

       *       *       *       *       *

To trace the geological sequence of the distribution of an ichthyic
type, and to recognise the various laws which have governed, and
are still governing its dispersal, is one of the ultimate tasks of
Ichthyology. But the endeavour to establish by means of our present
fragmentary geological knowledge the divisions of the fauna of the
globe, leads us into a maze of conflicting evidence; or, as Mr.
Wallace truly observes, “any attempt to exhibit the regions of former
geological ages in combination with those of our own period must lead
to confusion.” Nevertheless, as the different types of animals found
at the present day within a particular area have made their appearance
therein at distant periods, we should endeavour to decide as far as
we can, in an account of the several zoo-geographical divisions, the
following questions:--

1. Which of the fishes of an area should be considered to be the
remnants of _ancient_ types, probably spread over much larger areas in
preceding epochs?

2. Which of them are to be considered to be _autochthont_ species,
that is, forms which came in the tertiary epoch or later into existence
within the area to which they are still limited, or from which they
have since spread?

3. Which are the forms which must be considered to be _immigrants_
from some other region?

The mode of division of the earth’s surface into zoological regions
or areas now generally adopted, is that proposed by Mr. Sclater,
which recommends itself as most nearly agreeing with the geographical
divisions. These regions are as follows:--

   I. PALÆOGÆA.

      1. The _Palæarctic_ region; including Europe, temperate Asia,
           and North Africa.

      2. The _Ethiopian_ region; including Africa, south of the
           Sahara, Madagascar, and the Mascarene Islands; also
           Southern Arabia.

      3. The _Indian_ region; including India south of the
           Himalayas, to Southern China, Borneo, and Java.

      4. The _Australian_ region; including Australia, the
           Pacific Islands, Celebes, and Lombock.

   II. NEOGÆA.

      5. The _Nearctic_ region; including North America to
           Northern Mexico.

      6. The _Neotropical_ region; including South America, the West
           Indies, and Southern Mexico.

Comparatively few classes and orders of animals have been carefully
studied with regard to their geographical distribution, but the
majority of those which have been examined show that the difference
of latitude is accompanied by a greater dissimilarity of indigenous
species than that of longitude, and that a main division into an old
world and new world fauna is untenable. More especially the Freshwater
fishes, with which we are here solely concerned, have been spread in
_circumpolar_ zones, and in a but limited degree from north to
south. No family, much less a genus, ranges from the north to the
south, whilst a number of families and genera make the entire circuit,
and some species more than half of the circuit round the globe within
the zone to which they belong. Not even the Cyprinoids and Siluroids,
which are most characteristic of the freshwater fauna of our period,
are an exception to this. Temperature and climate, indeed, are the
principal factors by which the character of the freshwater fauna is
determined; they form the barriers which interfere with the unlimited
dispersal of an ichthyic type, much more than mountain ranges, deserts,
or oceans. Hence the tropical zone is an impassable barrier to the
northern Freshwater fish in its progress towards the south; where
a similarly temperate climate obtains in the southern hemisphere,
fish-forms appear _analogous_ to those of the north, but
_genetically_ and _structurally distinct_.

The similarity which obtains in fishes at somewhat distant points
of the same degree of longitude, rarely extends far, and is due to
the natural tendency of every animal to spread as far as physical
conditions will permit. Between two regions situated north and south
of each other there is always a debateable border ground, in parts of
which sometimes the fishes of the one, sometimes those of the other,
predominate, and which is, in fact, a _band_ of demarcation. Within
this band the regions overlap each other; therefore, their border
_lines_ are rarely identical, and should be determined by the northern
and southernmost extent of the most characteristic types of each
region. Thus, for instance, in China, a broad band intervenes between
temperate and tropical Asia, in which these two faunæ mix, and the
actual northern border line of the tropical fauna is north of the
southern border line of temperate Asia.

It is the aim of every philosophical classification to indicate the
degree of affinity which obtains between the various divisions; but
the mode of division into six equivalent regions, as given above, does
not fulfil this aim with regard to Freshwater fishes, the distribution
of which allows of further generalisation and subdivision. The two
families, _Cyprinidæ_ and _Siluridæ_, of which the former yields a
contingent of one-third, and the latter of one-fourth of all the
freshwater species known of our period, afford most valuable guidance
for the valuation of the degrees of affinity between the various
divisions. The Cyprinoids may be assumed to have taken their origin
in the Alpine region, dividing the temperate and tropical parts of
Asia; endowed with a greater capability of acclimatising themselves
in a temperate as well as tropical climate than any other family of
freshwater fishes, they spread north and south as well as east and
west; in the preglacial epoch they reached North America, but they have
not had time to penetrate into South America, Australia, or the islands
of the Pacific. The Siluroids, principally fishes of the sluggish
waters of the plains, and well adapted for surviving changes of the
water in which they live, for living in mud or sea-water, flourish
most in the tropical climate, in which this type evidently had its
origin. They came into existence after the Cyprinoids, fossil remains
being known only from tertiary deposits in India, none from Europe.
They rapidly spread over the areas of land within the tropical zone,
reaching northern Australia from India, and one species even immigrated
into the Sandwich Islands, probably from South America. The Coral
Islands of the Pacific still remain untenanted by them. Their progress
into temperate regions was evidently slow, only very few species
penetrating into the temperate parts of Asia and Europe; and the North
American species, although more numerous, showing no great variety
of structure, all belonging to the same group (_Amiurina_). Towards
the south their progress was still slower, Tasmania, New Zealand, and
Patagonia being without representatives, whilst the streams of the
Andes of Chili are inhabited by a few dwarfed forms identical with such
as are characteristic of similar localities in the more northern and
warmer parts of the South American continent.

After these preliminary remarks we propose the following division of
the fauna of Freshwater fishes:--

I. THE NORTHERN ZONE.--Characterised by Acipenseridæ. Few
     Siluridæ. Numerous Cyprinidæ. Salmonidæ, Esocidæ.

   1. _Europo-Asiatic or Palæarctic Region_.--Characterised by
        absence of osseous Ganoidei; Cobitidæ and Barbus numerous.

   2. _North American Region_.--Characterised by osseous Ganoidei,
        Amiurina, and Catostomina; but no Cobitidæ or Barbus.

II. THE EQUATORIAL ZONE.--Characterised by the development of
      Siluridæ.

   A. _Cyprinoid Division_.--Characterised by presence of Cyprinidæ
        and Labyrinthici.

     1. _Indian Region_.--Characterised by [absence of Dipnoi[18]]
          Ophiocephalidæ, Mastacembelidæ. Cobitidæ numerous.

     2. _African Region_.--Characterised by presence of Dipnoi and
          Polypteridæ. Chromides and Characinidæ numerous. Mormyridæ.
          Cobitidæ absent.

   B. _Acyprinoid Division_.--Characterised by absence of Cyprinidæ
        and Labyrinthici.

     1. _Tropical American Region_.--Characterised by presence of
          Dipnoi. Chromides and Characinidæ numerous. Gymnotidæ.

     2. _Tropical Pacific Region_.--Characterised by presence of
          Dipnoi. Chromides and Characinidæ absent.

III. THE SOUTHERN ZONE.--Characterised by absence of Cyprinidæ, and
       scarcity of Siluridæ. Haplochitonidæ and Galaxiidæ represent
       the Salmonoids and Esoces of the Northern zone. One region
       only.

   1. _Antarctic Region_.--Characterised by the small number of
        species; the fishes of--

     _a_. The Tasmanian sub-region;
     _b_. The New Zealand sub-region;
     _c_. The Patagonian sub-region;

being almost identical.[19]

In the following detailed account we begin with a description of the
equatorial zone, this being the one from which the two principal
families of freshwater fishes seem to have spread.

                          I. EQUATORIAL ZONE.

Roughly speaking, the borders of this zoological zone coincide with
the geographical limits of the tropical zone, the tropics of the
Cancer and Capricorn; its characteristic forms, however, extend in
undulating lines several degrees north and southwards. Commencing from
the west coast of Africa the desert of the Sahara forms a well-marked
boundary between the equatorial and northern zones; as the boundary
approaches the Nile it makes a sudden sweep towards the north as far
as Northern Syria (_Mastacembelus_, near Aleppo, and in the Tigris;
_Clarias_ and _Chromides_, in the lake of Galilee); crosses through
Persia and Afghanistan (_Ophiocephalus_), to the southern ranges of the
Himalayas, and follows the course of the Yang-tse-Kiang, which receives
its contingent of equatorial fishes through its southern tributaries.
Its continuation through the North Pacific may be considered to be
indicated by the tropic which strikes the coast of Mexico at the
southern end of the Gulf of California. Equatorial types of South
America are known to extend so far northwards; and by following the
same line the West India Islands are naturally included in this zone.

Towards the south the equatorial zone embraces the whole of Africa
and Madagascar, and seems to extend still farther south in Australia,
its boundary probably following the southern coast of that continent;
the detailed distribution of the freshwater fishes of South-Western
Australia has been but little studied, but the few facts which we
know show that the tropical fishes of Queensland follow the principal
water-course of that country, the Murray River, far towards the
south and probably to its mouth. The boundary-line then stretches
northwards of Tasmania and New Zealand, coinciding with the tropic
until it strikes the western slope of the Andes, on the South American
Continent, where it again bends southwards to embrace the system of the
Rio de la Plata.

The equatorial zone is divided into four regions:--

    A. The Indian region.
    B. The African region.
    C. The Tropical American region.
    D. The Tropical Pacific region.

These four regions diverge into two well-marked divisions, one of
which is characterised by the presence of Cyprinoid fishes, combined
with the development of Labyrinthici; whilst in the other both these
types are absent. The boundary between the Cyprinoid and Acyprinoid
division seems to follow Wallace’s line, a line drawn from the south of
the Philippines between Borneo and Celebes, and farther south between
Bali and Lombock. Borneo abounds in Cyprinoids; from the Philippine
Islands a few only are known at present, and in Bali two species have
been found; but none are known from Celebes or Lombock, or from islands
situated farther east of them.[20]

Taking into consideration the manner in which Cyprinoids and Siluroids
have been dispersed, we are obliged to place the Indian region as
the first in the order of our treatment; and indeed the number of
its freshwater fishes, which appear to have spread from it into the
neighbouring regions, far exceeds that of the species which it has
received from them.

       *       *       *       *       *

A. The INDIAN REGION comprises the whole continent of Asia south of
the Himalayas and the Yang-tse-kiang; it includes the islands to
the west of Wallace’s line. Towards the north-east the island of
Formosa, which also by other parts of its fauna leans more towards the
equatorial zone, has received some characteristic Japanese Freshwater
fishes, for instance, the singular Salmonoid _Plecoglossus_. Within
the geographical boundaries of China the Freshwater fishes of the
tropics pass gradually into those of the northern zone, both being
separated by a broad debateable ground. The affluents of the great
river traversing this district are more numerous from the south than
from the north, and carry the southern fishes far into the temperate
zone. The boundary of this region towards the north-west is scarcely
better defined. Before Persia passed through the geological changes
by which its waters were converted into brine and finally dried
up, it seems to have been inhabited by many characteristic Indian
forms, of which a few still survive in the tract intervening between
Afghanistan and Syria; _Ophiocephalus_ and _Discognathus_ have each
at least one representative, _Macrones_ has survived in the Tigris,
and Mastacembelus has penetrated as far as Aleppo. Thus, Freshwater
fishes belonging to India, Africa, and Europe, are intermingled in a
district which forms the connecting link between the three continents.
Of the freshwater fishes of Arabia we are perfectly ignorant; so much
only being known that the Indian _Discognathus lamta_ occurs in the
reservoirs of Aden, having, moreover, found its way to the opposite
African coast; and that the ubiquitous Cyprinodonts flourish in
brackish pools of Northern Arabia.

The following is the list of the forms of freshwater fishes inhabiting
this region:[21]--

    Percina--
        Lates[22] [Africa, Australia]                1 species.
    _Nandina_                                        7    „
    Labyrinthici [Africa]                            25   „
    _Luciocephalidæ_                                  1   „
    _Ophiocephalidæ_ [1 species in Africa]           30   „
    _Mastacembelidæ_ [3 species in Africa]           10   „
    Chromides [Africa, South America]
        _Etroplus_                                    2   „
    Siluridæ--
        Clariina [Africa]                            12   „
        _Chacina_                                     3   „
        Silurina [Africa, Palæarct.]                 72   „
        Bagrina [Africa]                             50   „
        Ariina [Africa, Australia, South America]    40   „
        _Bagariina_                                  20   „
        Rhinoglanina [Africa]                         1   „
        Hypostomatina [South America]                 5   „
    Cyprinodontidæ--
        Carnivoræ [Palæarct., North America,
        Africa, South America]
          Haplochilus [Africa, South America,
            North America, Japan]                     4   „
    Cyprinidæ [Palæarct., N. America, Africa]--
        Cyprinina [Palæarct., N. America, Africa]   190   „
        _Rasborina_ [Africa, 1 species]              20   „
        _Semiplotina_                                 4   „
        Danionina [Africa]                           30   „
        Abramidina [Palæarct., N. Amer., Africa]     30   „
        _Homalopterina_                              10   „
        Cobitidina [Palæarct.]                       50   „
    Osteoglossidæ [Africa, Australia, S. America]     1   „
    Notopteridæ [Africa]                              3   „
    Symbranchidæ--
        _Amphipnous_                                  1   „
        _Monopterus_                                  1   „
        Symbranchus [1 species in S. America]         2   „
                                                    ------------
                                                    625 species.
                                                    ============

In analysing this list we find that out of 39 families or groups of
freshwater fishes 12 are represented in this region, and that 625
species are known to occur in it; a number equal to two-sevenths of
the entire number of freshwater fishes known. This large proportion
is principally due to the development of numerous local forms of
Siluroids and Cyprinoids, of which the former show a contingent
of about 200, and the latter of about 330 species. The combined
development of those two families, and their undue preponderance over
the other freshwater types, is therefore the principal characteristic
of the Indian region. The second important character of its fauna is
the apparently total absence of Ganoid and Cyclostomous fishes. Every
other region has representatives of either Ganoids or Cyclostomes,
some of both. However, attention has been directed to the remarkable
coincidence of the geographical distribution of the _Sirenidæ_
and _Osteoglossidæ_, and as the latter family is represented in
Sumatra and Borneo, it may be reasonably expected that a Dipnoous form
will be found to accompany it. The distribution of the _Sirenidæ_
and _Osteoglossidæ_ is as follows:--

                 _Tropical America._

    Lepidosiren paradoxa.   |  Osteoglossum bicirrhosum.
                            |  Arapaima gigas.

                 _Tropical Australia._

    Ceratodus forsteri.     |  Osteoglossum leichardti.
    Ceratodus miolepis.

              _East Indian Archipelago._

        ?                   |  Osteoglossum formosum.

                 _Tropical Africa._

    Protopterus annectens.  |  Heterotis niloticus.

Not only are the corresponding species found within the same region,
but also in the same river systems; and although such a connection
may and must be partly due to a similarity of habit, yet the identity
of this singular distribution is so striking that it can only be
accounted for by assuming that the _Osteoglossidæ_ are one of the
earliest Teleosteous types which have been contemporaries of and have
accompanied the present Dipnoi since or even before the beginning of
the tertiary epoch.

Of the _autochthont_ freshwater fishes of the Indian region, some
are still limited to it, viz., the _Nandina_, the _Luciocephalidæ_
(of which one species only exists in the Archipelago), of Siluroids
the _Chacina_ and _Bagariina_, of Cyprinoids the _Semiplotina_ and
_Homalopterina_; others very nearly so, like the _Labyrinthici_,
_Ophiocephalidæ_, _Mastacembelidæ_, of Siluroids the _Silurina_, of
Cyprinoids the _Rasborina_ and _Danionina_, and _Symbranchidæ_.

The regions with which the Indian has least similarity are the North
American and Antarctic, as they are the most distant. Its affinity to
the other regions is of a very different degree:--

1. Its affinity to the Europo-Asiatic region is indicated almost solely
by three groups of Cyprinoids, viz., the _Cyprinina_, _Abramidina_,
and _Cobitidina_. The development of these groups north and south of
the Himalayas is due to their common origin in the highlands of Asia;
but the forms which descended into the tropical climate of the south
are now so distinct from their northern brethren that most of them are
referred to distinct genera. The genera which are still common to both
regions are only the true Barbels (_Barbus_), a genus which, of all
Cyprinoids, has the largest range over the old world, and of which some
160 species have been described; and, secondly, the Mountain Barbels
(_Schizothorax_, etc.), which, peculiar to the Alpine waters of Central
Asia, descend a short distance only towards the tropical plains, but
extend farther into rivers within the northern temperate districts. The
origin and the laws of the distribution of the _Cobitidina_ appear to
have been identical with those of _Barbus_, but they have not spread
into Africa.

If, in determining the degree of affinity between two regions, we take
into consideration the extent in which an exchange has taken place of
the faunæ originally peculiar to each, we must estimate that obtaining
between the freshwater fishes of the Europo-Asiatic and Indian regions
as very slight indeed.

2. There exists a great affinity between the Indian and African
regions; seventeen out of the twenty-six families or groups found in
the former are represented by one or more species in Africa, and many
of the African species are not even generically different from the
Indian. As the majority of these groups have many more representatives
in India than in Africa, we may reasonably assume that the African
species have been derived from the Indian stock; but this is probably
not the case with the Siluroid group of _Clariina_, which with regard
to species is nearly equally distributed between the two regions,
the African species being referable to three genera (_Clarias_,
_Heterobranchus_, _Gymnallabes_, with the subgenus _Channallabes_),
whilst the Indian species belong to two genera only, viz. _Clarias_
and _Heterobranchus_. On the other hand, the Indian region has derived
from Africa one freshwater form only, viz. _Etroplus_, a member of the
family of _Chromides_, so well represented in tropical Africa and South
America. _Etroplus_ inhabits Southern and Western India and Ceylon, and
has its nearest ally in a Madegasse Freshwater fish, _Paretroplus_.
Considering that other African Chromides have acclimatised themselves
at the present day in saline water, we think it more probable that
Etroplus should have found its way to India through the ocean than over
the connecting land area; where, besides, it does not occur.

3. A closer affinity between the Indian and Tropical American regions
than is indicated by the character of the equatorial zone generally,
does not exist. No genus of Freshwater fishes occurs in India and South
America without being found in the intermediate African region, with
two exceptions. Four small Indian Siluroids (_Sisor_, _Erethistes_,
_Pseudecheneis_, and _Exostoma_) have been referred to the South
American _Hypostomatina_; but it remains to be seen whether this
combination is based upon a sufficient agreement of their internal
structure, or whether it is not rather artificial. On the other hand,
the occurrence and wide distribution in tropical America of a fish of
the Indian family Symbranchidæ (_Symbranchus marmoratus_), which is
not only congeneric with, but also most closely allied to, the Indian
_Symbranchus bengalensis_, offers one of those extraordinary anomalies
in the distribution of animals of which no satisfactory explanation can
be given at present.

4. The relation of the Indian region to the Tropical Pacific region
consists only in its having contributed a few species to the poor fauna
of the latter. This immigration must have taken place within a recent
period, because some species now inhabit fresh waters of tropical
Australia and the South Sea Islands without having in any way changed
their specific characters, as _Lates calcarifer_, species of _Dules_,
_Plotosus anguillaris_; others (species of _Arius_) are but little
different from Indian congeners. All these fishes must have migrated
by the sea; a supposition which is supported by what we know of their
habits. We need not add that India has not received a single addition
to its freshwater fish-fauna from the Pacific region.

Before concluding these remarks on the Indian region, we must mention
that peculiar genera of Cyprinoids and Siluroids inhabit the streams
and lakes of its alpine ranges in the north. Some of them, like the
Siluroid genera _Glyptosternum_, _Euglyptosternum_, _Pseudecheneis_,
have a folded disk on the thorax between their horizontally spread
pectoral fins; by means of this they adhere to stones at the bottom of
the mountain torrents, and without it they would be swept away into
the lower courses of the rivers. The Cyprinoid genera inhabiting
similar localities, and the lakes into which the alpine rivers pass,
such as _Oreinus_, _Schizothorax_, _Ptychobarbus_, _Schizopygopsis_,
_Diptychus_, _Gymnocypris_, are distinguished by peculiarly enlarged
scales near the vent, the physiological use of which has not yet been
ascertained. These alpine genera extend far into the Europo-Asiatic
region, where the climate is similar to that of their southern home.
No observations have been made by which the altitudinal limits of fish
life in the Himalayas can be fixed, but it is probable that it reaches
the line of perpetual snow, as in the European Alps which are inhabited
by Salmonoids. Griffith found an _Oreinus_ and a Loach, the former in
abundance, in the Helmund at Gridun Dewar, altitude 10,500 feet; and
another Loach at Kaloo at 11,000 feet.

       *       *       *       *       *

B. THE AFRICAN REGION comprises the whole of the African continent
south of the Atlas and the Sahara. It might have been conjectured that
the more temperate climate of its southern extremity would have been
accompanied by a conspicuous difference of the fish-fauna. But this is
not the case; the difference between the tropical and southern parts
of Africa consists simply in the gradual disappearance of specifically
tropical forms, whilst Siluroids, Cyprinoids, and even Labyrinthici
penetrate to its southern coast; no new form has entered to impart
to South Africa a character distinct from the central portion of the
continent. In the north-east the African fauna passes the Isthmus of
Suez and penetrates into Syria; the system of the Jordan presenting
so many African types that it has to be included in a description of
the African region as well as of the Europo-Asiatic. This river is
inhabited by three species of _Chromis_, one of _Hemichromis_, and
_Clarias macracanthus_, a common fish of the Upper Nile. This infusion
of African forms cannot be accounted for by any one of those accidental
means of dispersal, as _Hemichromis_ is not represented in the
north-eastern parts of Africa proper, but chiefly on the west coast and
in the Central African lakes.

Madagascar clearly belongs to this region. Besides some Gobies and
_Dules_, which are not true freshwater fishes, four _Chromides_ are
known. To judge from general accounts, its Freshwater fauna is poorer
than might be expected; but, singular as it may appear, collectors
have hitherto paid but little attention to the Freshwater fishes of
this island. The fishes found in the freshwaters of the Seychelles
and Mascarenes are brackish-water fishes, such as _Fundulus_,
_Haplochilus_, _Elops_, _Mugil_, etc.

The following is the list of the forms of Freshwater fishes inhabiting
this region:--

    Dipnoi [Australia, Neotrop.]--
      _Lepidosiren annectens_                              1 species.

    _Polypteridæ_                                          2    „

    Percina (Cosmopol.)--
      Lates [India, Australia]                             1    „
    Labyrinthici [India]                                   5    „
    Ophiocephalidæ [India]                                 1    „
    Mastacembelidæ [India]                                 3    „

    Chromides [South America]--
      _Chromis_                                           23    „
      _Hemichromis_                                        5    „
      _Paretroplus_                                        1    „

    Siluridæ--
      Clariina [India]                                    14    „
      Silurina [India, Palæarct.]                         11    „
      Bagrina [India]                                     10    „
      Pimelodina [South America]                           2    „
      Ariina[23] [India, Australia, S. Amer., Patagonia]   4    „
      Doradina [South America]--
        _Synodontis_                                      15    „
      Rhinoglanina [India]                                 2    „
      _Malapterurina_                                      3    „

    Characinidæ [South America]--
      _Citharinina_                                        2    „
      _Nannocharacina_                                     2    „
      Tetragonopterina--
        _Alestes_                                         14    „
      Crenuchina--
        _Xenocharax_                                       1    „
      Hydrocyonina--
        _Hydrocyon_                                        4    „
      _Distichodontina_                                   10    „
      _Ichthyborina_                                       2    „

    _Mormyridæ_ (_Gymnarchidæ_)                           51    „

    Cyprinodontidæ--
      Carnivoræ [Palæarct., India, S. America--
        Haplochilus [India, South America]                 7    „
        Fundulus [Palæarct., Nearct.]                      1    „

    Cyprinidæ [Palæarct., India, North America]--
      Cyprinina [Palæarct., India, N. America--
        Labeo [India]                                      6    „
        Barynotus [India]                                  2    „
        _Abrostomus_                                       2    „
        Discognathus lamta[24] [India]                     1    „
        Barbus [Palæarct., India]                         35    „
      Rasborina [India]                                    1    „
      Danionina [India]--
        Barilius [India]                                   3    „
      Abramidina [Palæarct., India, N. America]--
        _Pelotrophus_                                      2    „

    _Kneriidæ_                                             2    „

    Osteoglossidæ [India, Australia, South America]--
      _Heterotis_                                          1    „

    _Pantodontidæ_                                         1    „

    Notopteridæ [India]                                    2    „
                                                          ------------
                                                          255 species.
                                                          ============

Out of the 39 families or groups of freshwater fishes 15 are
represented in the African region, or three more than in the Indian
region; however of two of them, viz., the _Ophiocephalidæ_ and
_Mastacembelidæ_, a few species only have found their way into
Africa. On the other hand, the number of species is much less, viz.
255, which is only two-fifths of that of the known Indian species. The
small degree of specialisation and localisation is principally due to
the greater uniformity of the physical conditions of this continent,
and to the almost perfect continuity of the great river systems,
which take their origin from the lakes in its centre. This is best
shown by a comparison of the fauna of the Upper Nile with that of the
West African rivers. The number of species known from the Upper Nile
amounts to 56, and of these not less than 25 are absolutely identical
with West African species. There is an uninterrupted continuity of the
fish-fauna from west to the north-east, and the species known to be
common to both extremities may be reasonably assumed to inhabit also
the great reservoirs of water in the centre of the continent. A greater
dissimilarity is noticeable between the west and north-east fauna
on the one hand, and that of the Zambezi on the other; the affinity
between them is merely generic; and all the fishes hitherto collected
in Lake Nyassa have proved to be distinct from those of the Nile, and
even from those of other parts of the system of the Zambezi.

Africa, unlike India, does not possess either alpine ranges or outlying
archipelagoes, the fresh waters of which would swell the number of its
indigenous species; but at a future time, when its fauna is better
known than at present, it is possible that the great difference in the
number of species between this and the Indian regions may be somewhat
lessened.

The most numerously-represented families are the Siluroids, with
61 species; the Cyprinoids, with 52; the Mormyridæ, with 51; the
Characinidæ, with 35; and the Chromides, with 29. There is not,
therefore, that great preponderance of the two first families over the
remaining, which we noticed in the Indian region; in Africa there is a
comparatively greater variety of distinct Freshwater types, imparting
to the study of its fauna an unflagging pleasure such as is scarcely
gained by the study of the other region. With the forms peculiar to it
there are combined those of India as well as South America.

In Tropical Africa there are still remnants of Ganoids: _Protopterus_
(_Lepidosiren_) _annectens_ and _Polypterus bichir_, with the
singularly modified _Calamoichthys_. The two former range from east to
west, and are accompanied by an Osteoglossoid (_Heterotis_) which has
hitherto been found in the Nile and on the West Coast only.

Autochthont and limited to this region are the _Mormyridæ_,
_Pantodontidæ_, and _Kneriidæ_, a singular type, somewhat akin to the
Loaches. Of Siluroid genera the most characteristic are _Synodontis_,
_Rhinoglanis_, and the electric _Malapterurus_; of Characinoids,
_Citharinus_, _Alestes_, _Xenocharax_, _Hydrocyon_, _Distichodon_,
_Ichthyborus_.

The regions with which Africa (like India) has least similarity
are, again, the North American and Antarctic. Its affinity with the
Europe-Asiatic region consists only in having received, like this
latter, a branch of the Cyprinoids, the African Carps and Barbels
resembling, on the whole, more Indian than Europo-Asiatic forms. Its
similarity to Australia is limited to the two regions possessing
Dipnoous and Osteoglossoid types. But its relations to the two other
regions of the equatorial zone are near and of great interest.

1. Africa has, in common with India, the Siluroid group of _Clariina_,
the _Silurina_, and _Bagrina_; and more especially the small but very
natural family of _Notopteridæ_, represented by three species in
India, and by two on the _west coast_ of Africa. It would be hazardous
to state at present in which of the two regions these fishes first
made their appearance, but the discovery of remains of _Notopteridæ_
and _Silurina_ in tertiary deposits of Sumatra points to the Indian
region as their original home. We can have less doubt about the other
fishes common to both regions; they are clearly immigrants into Africa
from the East, and it is a remarkable fact that these immigrants
have penetrated to the most distant limits of Africa in the west as
well as in the south,--viz. the _Labyrinthici_, represented by two
genera closely allied to the Indian _Anabas_; the _Ophiocephalidæ_
and _Mastacembelidæ_, a few species of which have penetrated to the
west coast, singularly enough being absent from the eastern rivers;
the _Ariina_, represented by several species, of which one or two
are identical with Indian, having extended their range along the
intervening coasts to the east coast of Africa. The Cyprinoids also
afford an instance of an Indian species ranging into Africa, viz.
_Discognathus lamta_, which seems to have crossed at the southern
extremity of the Red Sea, as it is found in the reservoirs at Aden and
the hill-streams of the opposite coast-region of Abyssinia.

2. No such direct influx of species and genera has occurred from
South America into Africa. Yet the affinity of their Freshwater
fishes is striking. Two of the most natural families of fishes, the
_Chromides_ and _Characinidæ_, are peculiar, and (with the exception of
_Etroplus_) restricted to them. The African and South American Dipnoi
are closely allied to each other. The _Pimelodina_, so characteristic
of Tropical America, have three representatives in Africa, viz.,
_Pimelodus platychir_, _P. balayi_, and _Auchenoglanis biscutatus_;
the _Doradina_ are another Siluroid group restricted to these two
continents.[25] Yet, with all these points of close resemblance, the
African and South American series are, with the exception of the two
species of Pimelodus, _generically_ distinct; which shows that the
separation of the continents must have been of an old date. On the
other hand, the existence of so many similar forms on both sides of
the Atlantic affords much support to the supposition that at a former
period the distance between the present Atlantic continents was much
less, and that the fishes which have diverged towards the East and
West are descendants of a common stock which had its home in a region
now submerged under some intervening part of that ocean. Be this as
it may, it is evident that the physical conditions of Africa and
South America have remained unchanged for a considerable period, and
are still sufficiently alike to preserve the identity of a number of
peculiar freshwater forms on both sides of the Atlantic. Africa and
South America are, moreover, the only continents which have produced in
Freshwater fishes, though in very different families, one of the most
extraordinary modifications of an organ--the conversion, that is, of
muscle into an apparatus creating electric force.

C. The boundaries of the TROPICAL AMERICAN (_Neotropical_) REGION
have been sufficiently indicated in the definition of the Equatorial
zone. A broad and most irregular band of country, in which the South
and North American forms are mixed, exists in the north; offering
some peculiarities which deserve fuller attention in the subsequent
description of the relations between the South and North American
faunæ. The following Freshwater fishes inhabit this region:--

    Dipnoi [Australia, Africa]--
      _Lepidosiren paradoxa_                           1 species.

    _Polycentridæ_                                     3    „

    Chromides [Africa]--
      _Heros_, _Acara_, _Cichla_, etc.                 80   „

    (_Lucifuga_                                        2    „)

    Siluridæ--
       _Hypophthalmina_                                5    „
          Pimelodina [Africa, 2 species]              70    „
          Ariina [Africa, India, Australia, Fuegian]  35    „
          Doradina [Africa]                           60    „
          Hypostomatina [India]                       90    „
       _Aspredinina_                                   9    „
          Nematogenyina [Fuegian]--                    2    „
          Trichomycterina [Fuegian]                    2    „
       _Stegophilina_                                  3    „
    Characinidae [Africa]--
       _Erythrinina_                                  15    „
       _Curimatina_                                   40    „
       _Anastomatina_                                 25    „
          Tetragonopterina                            80    „
          Hydrocyonina                                30    „
          Crenuchina                                   1    „
          Serrasalmonina                              35    „

    Cyprinodontidæ--
          Carnivoræ [Europe, Asia, N. America,
              India, Africa]                          30    „
       _Limnophagæ_                                   31    „
    Osteoglossidæ [Africa, India, Australia]           2    „
    _Gymnotidæ_                                       20    „
    Symbranchidæ [India]                               1    „
                                                     ------------
                                                     672 species.
                                                     ============

Out of the 39 families or groups of Freshwater fishes, 9 only are
represented in the Tropical American region. This may be accounted for
by the fact that South America is too much isolated from the other
regions of the Equatorial zone to have received recent additions to
its fauna. On the other hand, the number of species exceeds that of
every other region, even of the Indian, with which, in regard to the
comparative development of families, the Neotropical region shows great
analogy, as will be seen from the following Table:--

          INDIAN.               NEOTROPICAL.
    Siluridæ      200 sp.  Siluridæ       276 sp.
    Cyprinidæ     330 sp.  Characinidæ    226 sp.
    Labyrinthici   25 sp.  Chromides       80 sp.
    Ophiocephalidæ 30 sp.  Cyprinodontidæ  60 sp.
    Mastacembelidæ 10 sp.  Gymnotidæ       20 sp.

In both regions the great number of species is due to the development
of numerous local forms of two families, the _Characinidæ_ taking in
the New World the place of the _Cyprinidæ_ of the Old World. Thereto
are added a few smaller families with a moderately large number of
species, which, however, is only a fraction of that of the leading
families, the remainder of the families being represented by a few
species only. The number of genera within each of the two regions of
the two principal families is also singularly alike; the Indian region
having produced about 45 Siluroid and as many Cyprinoid genera, whilst
the Neotropical region is tenanted by 54 Siluroid and 40 Characinoid
genera. These points of similarity between the two regions cannot
be accidental; they indicate that agreement in their physical and
hydrographical features which in reality exists.

Of Ganoids, we find in Tropical America one species only, _Lepidosiren
paradoxa_, accompanied by two Osteoglossoids (_Osteoglossum
bicirrhosum_ and _Arapaima gigas_).

Autochthont and limited to this region are the _Polycentridæ_, all the
non-African genera of _Chromides_ and _Characinidæ_; of Siluroids, the
_Hypophthalmina_, _Aspredinina_, and _Stegophilina_, and the majority
of _Pimelodina_, _Hypostomatina_, and _Doradina_; the herbivorous
Cyprinodonts or _Limnophagæ_, and numerous insectivorous Cyprinodonts
or _Carnivoræ_; and the _Gymnotidæ_ (Electric eel).

The relations to the other regions are as follows:--

1. The resemblances to the Indian and Tropical Pacific regions partly
date from remote geological epochs, or are partly due to that
similarity of physical conditions to which we have already referred.
We have again to draw attention to the unexplained presence in South
America of a representative of a truly Indian type (not found in
Africa), viz. _Symbranchus marmoratus_. On the other hand, a
direct genetic affinity exists between the Neotropical and African
regions, as has been noticed in the description of the latter, a great
part of their freshwater fauna consisting of descendants from a common
stock.

2. A comparison of the specifically Neotropical with the specifically
North American types shows that no two regions can be more dissimilar.
It is only in the intervening borderland, and in the large West Indian
Islands, that the two faunæ mix with each other. We need not enter into
the details of the physical features of Central America and Mexico--the
broken ground, the variety of climate (produced by different altitudes)
within limited districts, the hot and moist alluvial plains surrounding
the Mexican Gulf, offer a diversity of conditions most favourable to
the intermixture of the types from the north and the south. But yet
the exchange of peculiar forms appears to be only beginning; none have
yet penetrated beyond the debatable ground, and it is evident that the
land-connection between the two continents is of comparatively recent
date: a view which is confirmed by the identity of the marine fishes on
both sides of Central America.

Cuba--and this is the only island in the West Indies which has a
number of freshwater fishes sufficient for the determination of its
zoo-geographical relations--is inhabited by several kinds of a perch
(_Centropomus_), freshwater mullets, Cyprinodonts, one species of
Chromid (an _Acara_), and _Symbranchus marmoratus_. All these fishes
are found in Central America, and as they belong to forms known to
enter brackish water more or less freely, it is evident that they
have crossed from the mainland of South America or from Central
America. But with them there came a remarkable North American type,
_Lepidosteus_. _Lepidosteus viridis_, which is found in the United
States, has penetrated on the mainland to the Pacific coast of
Guatemala, where it is common at the mouth of the rivers and in
brack-water lakes along the coast; it probably crossed into Cuba from
Florida. A perfectly isolated type of fishes inhabits the subterranean
waters of the caves of Cuba (two species of _Lucifuga_). The eyes are
absent or quite rudimentary, as in most other cave animals. Singularly,
it belongs to a family (_Ophidiidæ_), the members of which are strictly
marine; and its nearest ally is a genus, _Brotula_, the species of
which are distributed over the Indo-Pacific Ocean, one only occurring
in the Caribbean Sea. This type must have witnessed all the geological
changes which have taken place since Cuba rose above the surface of the
sea.

A similar mixture of forms of the Tropical and Temperate types of
Freshwater fishes takes place in the south of South America; its
details have not yet been so well studied as in the north; but this
much is evident that, whilst in the East Tropical forms follow the
Plate river far into the Temperate region, in the West the Temperate
Fauna finds still a congenial climate in ranges of the Andes, situated
close to, or even north of, the Tropic.

Like the Indian region, the Tropical American has a peculiar Alpine
Fauna, the Freshwater fishes of which, however, belong to the
Siluroids and Cyprinodonts. The former are small, dwarfed forms
(_Arges_, _Stygogenes_, _Brontes_, _Astroblepus_, _Trichomycterus_,
_Eremophilus_), and have a perfectly naked body, whilst the
representatives in the lowlands of, at least, the first four genera are
mailed. The Alpine Cyprinodonts, on the other hand, (_Orestias_) exceed
the usual small size of the other members of this family, are covered
with thick scales, but have lost their ventral fins. Some of these
Alpine forms, like _Trichomycterus_, follow the range of the Andes far
into the southern temperate region. The majority reach to a height
of 15,000 feet above the level of the sea, and a few are found still
higher.

D. The TROPICAL PACIFIC REGION includes all the islands east of
Wallace’s Line, New Guinea, Australia--with the exception of its
south-eastern portion,--and all the islands of the Tropical Pacific to
the Sandwich group. Comparing the area of this region with that of the
others, we find it to be not only the poorest in point of the number of
its species generally, but also in that of the possession of peculiar
forms, as will appear from the following list:--

    Dipnoi [Neotrop., Africa.]
      _Ceratodus_                                2 species.
    Percidæ [Cosmopol.]--
      Lates (calcarifer) [India]                 1    „
      _Nannoperca_                               1    „
      Oligorus [New Zealand]                     1    „
      Dules [India]                              8    „
      (_Macquaria_)                              1    „
    Labyrinthici--
      Anabas (scandens) [India]                  1    „
    Ophiocephalidæ--
      Ophiocephalus (striatus) [India]           1    „
    Atherinidæ [Brack-water]--
      Atherinichthys                             2    „
    Osteoglossidæ [India, Africa, Neotrop.]      1    „
    Siluridæ--
      Plotosina [India]                          9    „
      Ariina [India, Africa, Neotrop.]           7    „
    Symbranchidæ--
      Monopterus (javanicus) [India]             1    „
                                                -----------
                                        Total   36 species.

The paucity of freshwater fishes is due, in the first place, to the
arid climate and the deficiency of water in the Australian continent,
as well as to the insignificant size of the freshwater courses in the
smaller islands. Still this cannot be the only cause: the large island
of Celebes, which, by its mountainous portions, as well as by its
extensive plains and lowlands, would seem to offer a favourable variety
of conditions for the development of a freshwater Fauna is, as far as
has been ascertained, tenanted by seven Freshwater fishes only, viz. 2
_Arius_, 2 _Plotosus_, 1 _Andbas_, 1 _Ophiocephalus_, 1 _Monopterus_,
all of which are the commonest species of the Indian region. New
Guinea has not yet been explored, but, from the faunæ nearest to this
island, we expect its freshwater fishes will prove to be equally few
in number, and identical with those of Celebes and North Australia; a
supposition confirmed by the few small collections which have reached
Europe. Finding, then, that even those parts of this region, which
are favourable to the development of Freshwater fishes, have not
produced any distinct forms, and that the few species which inhabit
them, are unchanged, or but slightly modified Indian species, we must
conclude that the whole of this area has remained geologically isolated
from the other regions of this zone since the commencement of the
existence of Teleostei; and that, with the exception of _Ceratodus_ and
_Osteoglossum_, the immigration of the other species is of very recent
date.

Fossil remains of _Ceratodus_ have been found in Liassic and Triassic
formations of North America, England, Germany, and India; and it is,
therefore, a type which was widely spread in the Mesozoic epoch.
Although it would be rash to conclude that its occupation of Australia
dates equally far back, for it may have reached that continent long
afterwards; yet it is evident that, as it is one of the most ancient
of the existing types, so it is certainly the first of the Freshwater
fishes which appeared in Australia. _Osteoglossum_, of which no fossil
remains yet have been found, is proved by its distribution to be one
of the oldest Teleosteous types. There must have been a long gap of
time before these ancient types were joined by the other Teleostei.
All of them migrated through the intervening parts of the ocean from
India. Most of the _Plotosina_, some of the _Arii_, _Dules_, and
the _Atherinichthys_, also _Nannoperca_ (allied to _Apogon_), were
among the earliest arrivals, being sufficiently differentiated to
be specifically or even generically (_Cnidoglanis_, _Nannoperca_)
distinguished; but some others, like _Anabas scandens_, _Lates
calcarifer_, _Dules marginatus_, must have reached the Australian
continent quite recently, for they are indistinguishable from Indian
specimens.

In South-western Australia a mingling of the scanty fauna with that of
the southern temperate parts takes place. _Oligorus macquariensis_ (The
Murray Cod), which has a congener on the coast of New Zealand, ascends
high up the Murray river, so that we cannot decide whether this Percoid
should be located in the Tropical or Temperate part of Australia.
Several _Galaxias_ also extend to the confines of Queensland, and will
probably some day be found members of this region.

In the smaller Pacific islands the Freshwater fishes exhibit a
remarkable sameness: two or three species of _Dules_, several Eels, an
Atherine, or some Gobies, Mullets, and other fishes which with equal
readiness exchange fresh for salt water, and which would at once reach
and occupy any streams or freshwater lakes that may be formed on an
island.

The Sandwich Islands are the only group among the smaller islands which
are tenanted by a Siluroid, a species of _Arius_, which is closely
allied to Central American species, and, therefore, probably immigrated
from Tropical America.


                          II. NORTHERN ZONE.

The boundaries of the Northern Zone coincide in the main with the
northern limit of the Equatorial Zone; but at three different points
they overlap the latter, as has been already indicated. This happens
in, and east of, Syria, where the mixed faunæ of the Jordan and the
rivers of Mesopotamia demand the inclusion of this territory into the
Northern Zone as well as the Equatorial; in the island of Formosa,
where a Salmonoid and several Japanese Cyprinoids flourish; and in
Central America, where a _Lepidosteus_, a Cyprinoid (_Sclerognathus
meridionalis_), and an Amiurus (_A. meridionalis_) represent the North
American fauna in the midst of a host of tropical forms.

A separate _Arctic_ Zone does not exist for Freshwater fishes; ichthyic
life becomes extinct towards the pole as soon as the fresh water
remains frozen throughout the year, or thaws for a few weeks only; and
the few fishes which extend into high latitudes, in which lakes are
open for two or three months in the year, belong to types in no wise
differing from those of the more temperate south. The highest latitude
at which fishes have been obtained is 82° lat. N., whence the late
Arctic Expedition brought back specimens of Charr (_Salmo arcturus_ and
_Salmo naresii_).

The ichthyological features of this zone are well marked: the
Chondrosteous Ganoids or Sturgeons, and the families of _Salmonidæ_
and _Esocidæ_ are limited to, and characteristic of, it; Cyprinoids
flourish with the Salmonoids, both families preponderating in numbers
over the others, whilst the Siluroids are few in number and in variety.

The two regions in which this zone is divided are very closely related
to one another, and their affinity is not unlike that which obtains
between the sub-regions of the Southern Zone. The subjoined list will
show their close agreement with regard to families as well as species.
Several of the latter are common to both, viz.--_Acipenser sturio_,
_A. maculatu_s, _Perca fluviatilis_, _Gastrosteus pungitius_, _Salmo
salar_, _Esox lucius_, _Lota vulgaris_, _Petromyzon marinus_, _P.
fluviatilis_, and _P. branchialis_; and all recent investigations have
resulted in giving additional evidence of the affinity, and not of the
diversity of the two regions.

In Europe and temperate Asia, as well as in North America, mountain
ranges elevated beyond the line of perpetual snow would seem to offer
physical conditions favourable for the development of a distinct
alpine fauna. But this is not the case, because the difference of
climate between the mountain districts and the lowlands is much less in
this zone than in the Equatorial. Consequently the alpine freshwater
fishes do not essentially differ from those of the plains; they are
principally Salmonoids; and in Asia, besides, mountain-barbels and
Loaches. _Salmo orientalis_ was found by Griffith to abound in the
tributaries of the Bamean river at an altitude of about 11,000 feet.


                                       Europo-Asiatic.   N. American.
    _Acipenseridæ_--
      Acipenser                          9 species.      12 species.
      Scaphirhynchus                     2    „           1    „
      Polyodon                           1    „           1    „
    _Lepidosteidæ_                       0    „           3    „
    _Amiidæ_                             0    „           1    „
    Percina [Cosmopol.]                 10    „          30    „
    Grystina [Australia, New Zealand]    0    „           2    „
    _Centrarchina_                       0    „          26    „
    _Aphredoderidæ_                      0    „           1    „
    Cottidæ [partly marine]--
      _Cottus_                           3    „           8    „
      _Ptyonotus_                        0    „           1    „
    _Gastrosteidæ_                       5    „           5    „
    _Comephoridæ_                        1    „           0    „
    Gadidæ [marine]--
      _Lota_                             1    „           1    „
    Siluridæ--
      Silurina [India, Africa]           5    „           0    „
      Bagrina                            2    „           0    „
      _Amiurina_                         1    „          17    „
    _Salmonidæ_                         90    „          45    „
    _Percopsidæ_                         0    „           1    „
    _Esocidæ_                            1    „           7    „
    _Umbridæ_                            1    „           1    „
    Cyprinodontidæ Carnivoræ [India,
      Africa, Neotrop.]                  9    „          30    „
    _Heteropygii_                        0    „           2    „
    Cyprinidæ--
      _Catostomina_                      1    „          25    „
      Cyprinina [India, Africa]         80    „          30    ”
      _Leuciscina_                      60    „          70    „
      _Rhodeina_                        10    „           0    „
      Abramidina [India, Africa]        44    „          10    ”
      Cobitidina [India]                20    „           0    ”
    _Hyodontidæ_                         0    „           1    „
    Petromyzontidæ [Southern Zone]       4    „           8    ”
                                       -----------------------------
                                       360 species.     339 species.
                                       =============================

A. THE EUROPO-ASIATIC (PALÆARCTIC) REGION.--Its western and
southern boundaries coincide with those of the Northern Zone, so that
only those which divide it from North America have to be indicated.
Behring’s Strait and the Kamtschatka Sea have been conventionally
taken as the boundary, but this is shown to be artificial by the fact
that the animals of both coasts, as far as they are known at present,
are not sufficiently distinct to be referred to two distinct regions.
As to the freshwater fishes those of North-western America and of
Kamtschatka are but imperfectly known, but there can be little doubt
that the same agreement exists between them as is the case with other
classes of animals. The Japanese islands exhibit a decided Palæarctic
fish-fauna, which includes Barbus and Cobitioids, forms strange to the
North American fauna. A slight influx of tropical forms is perceived in
the south of Japan, where two Bagrina (_Pseudobagrus aurantiacus_
and _Liocassis longirostris_) have established themselves for a
considerable period, for both are peculiar to the island, and have not
been found elsewhere.

In the east, as well as in the west, the distinction between the
Europo-Asiatic and North American regions disappears almost entirely
the farther we advance towards the north. Of four species of the genus
Salmo known from Iceland, one (_S. salar_) is common to both regions,
two are European (_S. fario_ and _S. alpinus_), and one is a peculiarly
Icelandic race (_S. nivalis_). As far as we know the Salmonoids of
Greenland and Baffin’s Land they are all most closely allied to
European species, though they may be distinguished as local races.

Finally, as we have seen above, the Europo-Asiatic fauna mingles with
African and Indian forms in Syria, Persia, and Afghanistan. _Capoëta_,
a Cyprinoid genus, is characteristic of this district, and well
represented in the Jordan and rivers of Mesopotamia.

Assuming that the distribution of Cyprinoids has taken its origin from
the alpine tract of country dividing the Indian and Palæarctic regions,
we find that this type has found in the temperate region as equally
favourable conditions for its development as in the tropical. Out of
the 360 species known to exist in the Palæarctic regions, no less than
215 are Cyprinoids. In the countries and on the plateaus immediately
joining the Himalayan ranges those mountain forms which we mentioned
as peculiar to the Indian Alps abound and extend for a considerable
distance towards the west and east, mixed with other _Cyprinina_
and _Cobitidina_. The representatives of these two groups are more
numerous in Central and Eastern Asia than in Europe and the northern
parts of Asia, where the _Leuciscina_ predominate. _Abramidina_ or
Breams are more numerous in the south and east of Asia, but they
spread to the extreme north-western and northern limits, to which the
Cyprinoid type reaches. The _Rhodeina_ are a small family especially
characteristic of the East, but with one or two off-shoots in Central
Europe. Very significant is the appearance in China of a species of the
_Catostomina_, a group otherwise limited to North America.

The Cyprinoids, in their dispersal from the south northwards, are
met from the opposite direction by the Salmonoids. These fishes are,
without doubt, one of the youngest families of _Teleostei_, for they
did not appear before the Pliocene era; they flourished at any rate
during the glacial period, and, as is testified by the remnants which
we find in isolated elevated positions, like the Trout of the Atlas,
of the mountains of Asia-Minor, and of the Hindu Kush, they spread to
the extreme south of this region. At the present day they are most
numerously represented in its northern temperate parts; towards the
south they become scarcer, but increase again in numbers and species,
wherever a great elevation offers them the snow-fed waters which they
affect. In the rivers of the Mediterranean Salmonoids are by no means
scarce, but they prefer the upper courses of those rivers, and do not
migrate to the sea.

The Pike, Umbra, several species of Perch and Stickleback, are also
clearly autochthont species of this region. Others belong to marine
types, and seem to have been retained in fresh water at various epochs:
thus the freshwater Cottus (Miller’s Thumb); _Cottus quadricornis_,
which inhabits lakes of Scandinavia, whilst other individuals of the
same species are strictly marine; the Burbot (_Lota vulgaris_); and the
singular _Comephorus_, a dwarfed and much-changed Gadoid which inhabits
the greatest depths of Lake Baikal.

Remnants of the Palæichthyic fauna are the _Sturgeons_ and _Lampreys_.
The former inhabit in abundance the great rivers of Eastern Europe and
Asia, periodically ascending them from the sea; their southernmost
limits are the Yangtse-kiang in the east, and rivers flowing into the
Adriatic, Black and Caspian Seas, and Lake Aral, towards the centre of
this region. None are known to have gone beyond the boundaries of the
Northern Zone. If the Lampreys are justly reckoned among Freshwater
fishes, their distribution is unique and exceptional. In the Palæarctic
region some of the species descend periodically to the sea, whilst
others remain stationary in the rivers; the same has been observed
in the Lampreys of North America. They are entirely absent in the
Equatorial Zone, but reappear in the Temperate Zone of the Southern
Hemisphere. Many points of the organisation of the Cyclostomes indicate
that they are a type of great antiquity.

The remaining Palæarctic fishes are clearly immigrants from
neighbouring regions: thus _Silurus_, _Macrones_, and _Pseudobagrus_
from the Indian region; _Amiurus_ (and, as mentioned above,
_Catostomus_) from North America. The Cyprinodonts are restricted to
the southern and warmer parts; all belong to the carnivorous division.
The facility with which these fishes accommodate themselves to a
sojourn in fresh, brackish, or salt water, and even in thermal springs,
renders their general distribution easily comprehensible, but it is
impossible to decide to which region they originally belonged; their
remains in tertiary deposits round the Mediterranean are not rare.

       *       *       *       *       *

_B_. The boundaries of the NORTH AMERICAN or NEARCTIC REGION have
been sufficiently indicated. The main features and the distribution
of this fauna are identical with those of the preceding region. The
proportion of Cyprinoid species to the total number of North-American
fishes (135:339) appears to be considerably less than in the Palæarctic
region, but we cannot admit that these figures approach the truth,
as the Cyprinoids of North America have been much less studied than
those of Europe; of many scarcely more than the name is known. This
also applies in a great measure to the Salmonoids, of which only half
as many as are found in the Palæarctic region have been sufficiently
described to be worthy of consideration. North America will, without
doubt, in the end show as many distinct races as Europe and Asia.

Cyprinoids, belonging to genera living as well as extinct, existed
in North America in the tertiary period. At present, _Cyprinina_,
_Leuciscina_, and _Abramidina_ are well represented, but there
is no representative of the Old World genus _Barbus_, or of the
_Cobitidina_[26]; _Rhodeina_ are also absent. On the other hand, a
well-marked Cyprinoid type is developed--the _Catostomina_, of which
one species has, as it were, returned into Asia. Very characteristic is
the group of _Centrarchina_, allied to the Perch, of which there are
some thirty species; two _Grystina_. Of the Sticklebacks there are as
many species as in Europe, and of Pike not less than seven species have
been distinguished. _Umbra_ appears to be as local as in Europe. Some
very remarkable forms, types of distinct families, though represented
by one or two species only, complete the number of North American
autochthont fishes--viz., _Aphredoderus_, _Percopsis_, _Hyodon_, and
the _Heteropygii_ (_Amblyopsis_ and _Chologaster_). The last are
allied to the Cyprinodonts, differing from them in some points of the
structure of their intestines. The two genera are extremely similar,
but _Chologaster_, which is found in ditches of the rice-fields of
South Carolina, is provided with eyes, and lacks the ventral fins.
_Amblyopsis_ is the celebrated Blind Fish of the Mammoth Cave of
Kentucky: colourless, eyeless, with rudimentary ventral fins, which may
be occasionally entirely absent.

A peculiar feature of the North American Fish Fauna is that it has
retained, besides the Sturgeons and Lampreys, representatives of two
Ganoid families, _Lepidosteus_ and _Amia_. Both these genera existed
in tertiary times: the former occurs in tertiary deposits of Europe as
well as North America, whilst fossil remains of _Amia_ have been found
in the Western Hemisphere only.

It is difficult to account for the presence of the _Amiurina_ in North
America. They form a well-marked division of the _Bagrina_, which
are well represented in Africa and the East Indies, but absent in
South America; it is evident, therefore, they should not be regarded
as immigrants from the south, as is the case with the Palæarctic
Siluroids. Nor, again, has the connection between South and North
America been established sufficiently long to admit of the supposition
that these Siluroids could have spread in the interval from the south
to the northern parts of the continent, for some of the species are
found as far north as Pine Islands Lake (54° lat. N.)[27]


                          III. SOUTHERN ZONE.

The boundaries of this zone have been indicated in the description of
the Equatorial Zone; they overlap the southern boundaries of the latter
in South Australia and South America, but we have not at present the
means of exactly defining the limits to which southern types extend
northwards. This zone includes Tasmania with at least a portion of
South-eastern Australia (_Tasmanian sub-region_), New Zealand and the
Auckland Islands (_New Zealand sub-region_), and Chili, Patagonia,
Terra del Fuego, and the Falkland Islands (_Fuegian sub-region_). No
freshwater fishes are known from Kerguelen’s Land, or from islands
beyond 55° lat. S. The southern extremity of Africa has to be excluded
from this zone so far as Freshwater fishes are concerned.

This zone is, with regard to its extent as well as to the number of
species, the smallest of the three; yet its ichthyological features
are well marked; they consist in the presence of two peculiar
families, each of which is analogous to a northern type, viz. the
_Haplochitonidæ_, which represent the _Salmonidæ_, _Haplochiton_ being
the analogue of _Salmo_, and _Prototroctes_ that of _Coregonus_; and
the _Galaxiidæ_, which are the Pikes of the Southern Hemisphere.

Although geographically widely separate from each other, the Freshwater
fishes of the three divisions are nevertheless so closely allied
that conclusions drawn from this group of animals alone would hardly
justify us in regarding these divisions as sub-regions. One species of
_Galaxias_ (_G. attenuatus_) and the three Lampreys are found in all
three, or at least two, sub-regions.

            _Freshwater Fishes of the Southern Zone._

                                  Tasmanian. N. Zealand. Fuegian.

    _Percichthys_                    ...          ...         3

    Siluridæ--
      _Diplomystax_                  ...          ...         1
      _Nematogenys_                  ...          ...         1
      Trichomycterina [Neotrop.]     ...          ...         5

    _Gadopsidæ_                        1          ...       ...

    (_Retropinna_                    ...            1       ...)

    _Haplochitonidæ_                   1            1          1

    _Galaxiidæ_                        6            5          4

    Petromyzontidæ                     3            1          3
                                      --           --         --
                                      11            8         18

But little remains to be added in explanation of this list;
_Percichthys_ is in Chili the autochthont form of the cosmopolitan
group of _Percina_. _Diplomystax_, an Arioid fish of Chili, and
_Nematogenys_ seem to have crossed the Andes from Tropical America
at a comparatively early period, as these genera are not represented
on the eastern side of South America; the _Trichomycterina_ occur on
both sides of the Andes, which they ascend to a considerable height.
_Retropinna_ is a true Salmonoid, allied to, and representing in the
Southern Hemisphere the Northern Smelt, _Osmerus_. In both these
genera a part of the specimens live in the sea, and ascend rivers
periodically to spawn; another part remain in rivers and lakes, where
they propagate, never descending to the sea, this freshwater race
being constantly smaller than their marine brethren. That this small
Teleostean of the Northern Hemisphere should reappear, though in a
generically modified form, in New Zealand, without having spread over
other parts of the Southern Zone, is one of the most remarkable, and
at present inexplicable facts of the geographical distribution of
freshwater fishes.

  [Illustration: Fig. 104.--_Haplochiton zebra_, Straits of
  Magelhæn.]




                            CHAPTER XVIII.

                   THE FISHES OF THE BRACKISH WATER.


On such parts of a coast at which there is a mixture of fresh and salt
water, either in consequence of some river emptying its water into the
sea or from an accumulation of land surface water forming lagunes,
which are in uninterrupted or temporary communication with the sea,
there flourishes a peculiar brackish water fauna which is characterised
by the presence of fishes found sometimes in sea-, sometimes in pure
freshwater.

This fauna can be rather sharply defined if a limited district only
is taken into consideration; thus, the species of the brackish water
fauna of Great Britain, the Pacific coast of Central America, of
the larger East India Islands, etc., can be enumerated without much
hesitation. But difficulties arise when we attempt to generalise in the
enumeration of the forms referable to the brackish water fauna; because
the genera and families enumerated include certain species and genera
which have habituated themselves exclusively either to a freshwater or
marine existence; and, besides, because a species of fish may be at
one locality an inhabitant of brackish water, at another of the sea,
and at a third of fresh water. The circumstance that these fishes can
live in sea and fresh water has enabled them to spread readily over the
globe, a few only being limited to particular regions; therefore, for
the purposes of dividing the earth’s surface into natural zoological
regions the brackish water forms are useless. The following fishes may
be referred to this Fauna:--

1. Species of _Rajidæ_ (_Raja_, _Trygon_) prefer the mouths of rivers,
probably because the muddy or sandy bottom offers the most suitable
conditions for fishes which can feed on the bottom only; such brackish
water species belong chiefly to the Equatorial Zone, some having taken
up their abode entirely in fresh water (South American Trygons).

2. _Ambassis_, a Percoid genus, consisting of numerous small species,
inhabiting the shores of the tropical parts of the Indian Ocean and
the coasts of Tropical Australia. Many species enter, and all seek the
neighbourhood of, fresh water; hence they disappear in the islands of
the Pacific, and are scarce in the Red Sea.

3. _Therapon_, with the same distribution as the former.

4. Numerous _Sciænidæ_ of the Equatorial Zone.

5. The _Polynemidæ_, chiefly inhabitants of brackish water of the
Equatorial Zone, most developed in the Indian region, and scarce in the
Tropical Pacific.

6. Numerous species of _Caranx_ (or Horse Mackerels) of the Equatorial
Zone.

7. Nearly all species of _Gastrosteus_ enter brackish water, _G.
spinachia_ being almost exclusively confined to it: Northern Zone.

8. The most important genera of the Gobies (_Gobiina_): _Gobius_
(nearly cosmopolitan), _Sicydium_, _Boleophthalmus_, _Periophthalmus_,
_Eleotris_ (equatorial). Many of the species are entirely confined to
fresh water.

9. The _Amblyopina_, similar to the Gobies, but with more elongated
body: Tropical Indo-Pacific.

10. The _Trypauchenina_: Coasts of the Indian region.

11. Many species of _Blennius_, of which several are found far inland
in fresh waters--for instance in North Italy, in the Lake of Galilee,
in the eastern parts of Asia Minor.

12. The majority of _Atherinidæ_, and

13. The _Mugilidæ_: both families being most numerous and abundant in
brackish water, and almost cosmopolitan.

14. Many _Pleuronectidæ_ prefer the mouths of rivers for the same
reason as the Rays; some ascend rivers, as the Flounder, _Cynoglossus_,
etc.

15. Several _Siluridæ_, as especially the genera _Plotosus_,
_Cnidoglanis_, _Arius_, which attain their greatest development in
brackish water.

16. The _Cyprinodontidæ_ are frequently found in brackish water.

17. Species of _Clupea_, some of which ascend rivers, and become
acclimatized in fresh water, as _Clupea finta_, which has established
itself in the lakes of northern Italy.

18. _Chatoessus_, a genus of Clupeoid fishes of the Equatorial Zone, of
which some species have spread into the Northern Zone.

19. _Megalops_: Equatorial Zone.

20. _Anguilla._ The distribution, no less than the mode of propagation,
and the habits generally, of the so-called Freshwater-eels still
present us with many difficult problems. As far as we know at present
their birthplace seems to be the coast in the immediate neighbourhood
of the mouths of rivers. They are much more frequently found in fresh
water than in brackish water, but the distribution of some species
proves that they at times migrate by sea as well as by land and river.
Thus _Anguilla mauritiana_ is found in almost all the fresh and
brackish waters of the islands of the Tropical Indian Ocean and Western
Pacific, from the Comoros to the South Sea; _Anguilla vulgaris_ is
spread over temperate Europe (exclusive of the system of the Danube,
the Black and Caspian Seas), in the Mediterranean district (including
the Nile and rivers of Syria), and on the Atlantic coast of North
America; _Anguilla bostoniensis_, in Eastern North America, China,
and Japan; _Anguilla lati__rostris_, in Temperate Europe, the whole
Mediterranean district, the West Indies, China, and New Zealand. The
other more local species are found, in addition to localities already
mentioned, on the East Coast of Africa, South Africa, on the continent
of India, various East Indian Islands, Australia, Tasmania, Auckland
Islands; but none have ever been found in South America, the West Coast
of North America, and the West Coast of Africa: surely one of the most
striking instances of irregular geographical distribution.

21. Numerous _Syngnathidæ_ have established themselves in the Northern
Zone as well as in the Equatorial, in the vegetation which flourishes
in brackish water.

This list could be considerably increased if an enumeration of species,
especially of certain localities, were attempted; but this is more a
subject of local interest, and would carry us beyond the scope of a
general account of the distribution of Fishes.

  [Illustration: Fig. 105.--_Mugil octo-radiatus._]

  [Illustration: Fig. 106.--_Mugil auratus._]

  [Illustration: Fig. 107.--_Mugil septentrionalis._

   Heads of Grey Mullets, fishes of Brackish water.]




                             CHAPTER XIX.

                  THE DISTRIBUTION OF MARINE FISHES.


Marine fishes fall, with regard to their mode of life and distribution,
into three distinct categories:--

1. _Shore Fishes_--That is, fishes which inhabit chiefly parts of the
sea in the immediate neighbourhood of land either actually raised
above, or at least but little submerged below, the surface of the
water. They do not descend to any great depth,--very few to 300
fathoms, and the majority live close to the surface. The distribution
of these fishes is determined not only by the temperature of the
surface water but also by the nature of the adjacent land, and its
animal and vegetable products; some of these fishes being confined to
flat coasts with soft or sandy bottoms, others to rocky and fissured
coasts, others to living coral formations. If it were not for the
frequent mechanical and involuntary removals to which these fishes
are exposed, their distribution within certain limits, as it no doubt
originally existed, would resemble still more that of freshwater fishes
than we find it actually does at the present period.

2. _Pelagic Fishes_--that is, fishes which inhabit the surface and
uppermost strata of the open ocean, which approach the shores only
accidentally, or occasionally (in search of prey), or periodically
(for the purpose of spawning). The majority spawn in the open sea,
their ova and young being always found at great distance from the
shore. With regard to their distribution, they are still subject to
the influences of light and the temperature of the surface water; but
they are independent of the variable local conditions which tie the
shore fish to its original home, and therefore roam freely over a space
which would take a freshwater or shore fish thousands of years to cover
in its gradual dispersal. Such as are devoid of rapidity of motion
are dispersed over similarly large areas by the oceanic currents,
more slowly than, but as surely as, the strong swimmers. Therefore,
an accurate definition of their distribution within certain areas
equivalent to the terrestrial regions is much less feasible than in the
case of shore fishes.

3. _Deep-sea Fishes_--that is, fishes which inhabit such depths of the
ocean as to be but little or not influenced by light or the surface
temperature; and which, by their organisation are prevented from
reaching the surface stratum in a healthy condition. Living almost
under identical tellurian conditions, the same type, the same species,
may inhabit an abyssal depth under the equator as well as one near the
arctic or antarctic circle; and all we know of these fishes points to
the conclusion that no separate horizontal regions can be distinguished
in the abyssal fauna, and that no division into bathymetrical strata
can be attempted on the base of generic much less of family characters.

It must not be imagined that these three categories are more sharply
defined than Freshwater and Marine Fishes. They gradually pass into
each other, and there are numerous fishes about which uncertainty
exists whether they should be placed in the Shore or Pelagic series, or
in the Pelagic or Deep-sea series; nay, many facts favour the view that
changes in the mode of life and distribution of fishes are still in
progress.

The change in habitat of numerous fishes is regulated by the
distribution of their favourite food. At certain seasons the surface
of the sea in the vicinity of land swarms with mollusks, larval
Crustaceans, Medusæ, attracting shoals of fishes from the open ocean
to the shores; and these are again pursued by fishes of larger size and
predacious habits, so that all these fishes might be included, with
equal propriety, in the littoral or pelagic series. However, species
which are known to normally spawn in the open ocean must be always
referred to the latter division.

Chondropterygii, Acanthopterygii, Anacanths, Myxinoids, and
Pharyngobranchii furnish the principal contingents to the Marine Fauna;
whilst the majority of Malacopterygians, the Ganoids, and Cyclostomes
are Freshwater Fishes.


                   I.--DISTRIBUTION OF SHORE FISHES.

       The principal types of Shore-fishes are the following:--

    CHONDROPTERYGII--
      HOLOCEPHALA                                  4 species
      PLAGIOSTOMATA--
        _Carchariidæ_ (part.)                     12    „
        _Scylliidæ_                               30    „
        _Cestraciontidæ_                           4    „
        _Spinacidæ_ (part.)                        8    „
        _Rhinidæ_                                  1    „
        _Pristiophoridæ_                           4    „
        _Pristidæ_                                 5    „
        _Rhinobatidæ_                             14    „
        _Torpedinidæ_                             15    „
        _Rajidæ_                                  34    „
        _Trygonidæ_                               47    „

    ACANTHOPTERYGII--
      _Percidæ_ (part. incl. Pristipomatidæ)     625    „
      _Mullidæ_                                   35    „
      _Sparidæ_                                  130    „
      _Squamipinnes_                             130    „
      _Cirrhitidæ_                                40    „
      _Heterolepidina_                            12    „
      _Scorpænidæ_                               120    „
      _Cottiæ_ (part.)                           100    „
      _Cataphracti_ (part.)                       20    „
      _Trachinidæ_                               100    „
      _Sciænidæ_                                 100    „
      _Sphyrænidæ_                                15    „
      _Trichiuridæ_                               17    „
      _Elacate_                                    1    „
      _Nomeidæ_ (part.)                            5    „
      _Cyttidæ_                                    8    „
      _Stromateus_                                 9    „
      _Mene_                                       1    „
      _Carangidæ_ (part.)                        130    „
      _Kurtidæ_                                    7    „
      _Gobiodon_                                   7    „
      _Callionymina_                              30    „
      _Discoboli_                                 11    „
      _Batrachidæ_                                14    „
      _Pediculati_ (part.)                        11    „
      _Blenniidæ_                                 90    „
      _Acanthoclinidæ_                             1    „
      _Teuthididæ_                                30    „
      _Acronuridæ_                                60    „
      _Hoplognathidæ_                              3    „
      _Malacanthidæ_                               3    „
      _Plesiopina_                                 4    „
      _Trichonotidæ_                               2    „
      _Cepolidæ_                                   7    „
      _Gobiesocidæ_                               21    „
      _Psychrolutidæ_                              2    „
      _Centriscidæ_                                7    „
      _Fistulariidæ_                               4    „

    ACANTHOPTERYGII PHARYNGOGNATHI--

        _Pomacentridæ_                           150    „
        _Labridæ_                                400    „
        _Embiotocidæ_                             17    „

    ANACANTHINI--

        _Gadopsidæ_                                1    „
        _Lycodidæ_                                15    „
        _Gadidæ_ (part.)                          50    „
        _Ophidiidæ_ (part.)                       40    „
        _Pleuronectidæ_                          160    „

    PHYSOSTOMI--

        _Saurina_ (part.)                         16    „
        _Salmonidæ_ (part.)                        7    „
        _Clupeidæ_ (part.)                       130    „
        _Chirocentridæ_                            1    „
        _Chilobranchus_                            1    „
        _Murænidæ_ (part.)                       200    „
        _Pegasidæ_                                 4    „

    LOPHOBRANCHII                                120    „

    PLECTOGNATHI--

        _Sclerodermi_                             95    „
        _Gymnodontes_                             83    „

    CYCLOSTOMATA--

        MYXINIDÆ                                   5    „

    LEPTOCARDII                                    2    „
                                                -------------
                                                3587 species.
                                                =============

These types of Shore fishes are divided among the following oceanic
areæ:--

       I. The Arctic Ocean.

      II. The Northern Temperate Zone.

            A. The Temperate North Atlantic.
                 1. The British district.
                 2. The Mediterranean district.
                 3. The North American district.

            B. The Temperate North Pacific.
                 1. The Kamtschatkan district.
                 2. The Japanese district.
                 3. The Californian district.

    III. The Equatorial Zone.
         A. The Tropical Atlantic.
         B. The Tropical Indo-Pacific.
         C. The Pacific Coast of Tropical America.
             1. The Central American district.
             2. The Galapagoes district.
             3. The Peruvian district.

    IV. The Southern Temperate Zone.
             1. The Cape of Good Hope district.
             2. The South Australian district.
             3. The Chilian district.
             4. The Patagonian district.

    V. The Antarctic Ocean.

As with freshwater fishes, the main divisions of the Shore-fish faunæ
are determined by their distance from the equator, the equatorial
zone of the Freshwater series corresponding entirely to that of
the Shore-fish series. But as Marine fishes extend farther towards
the Poles than Freshwater fishes, and as the polar types are more
specialised, a distinct Arctic and Antarctic fauna may be separated
from the faunæ of the temperate zones. The two subdivisions of the
Northern temperate zone in the Freshwater series are quite analogous
to the corresponding divisions in the Coast series. In the Southern
Hemisphere the Shore-fishes of the extremity of Africa form a separate
district of the temperate zone, whilst the Freshwater fishes of
South Africa were found to be tropical types. The Marine series of
the Southern temperate zone is also much more diversified than the
Freshwater series, and admits of further subdivision, which, although
in some degree indicated in the Freshwater series, does not entirely
correspond to that proposed for the latter.


                 I. SHORE FISHES OF THE ARCTIC OCEAN.

The Shore fishes clearly prove a continuity of the Arctic circumpolar
fauna, as the southern limit of which we may indicate the southern
extremity of Greenland and the Aleutian Archipelago, or 60° of lat. N.

Towards the North, fishes become less in variety of species and fewer
in number of individuals, and only very few genera are restricted to
this fauna.

The highest latitude at which Shore fishes have been observed is
83° N. lat. The late Arctic Expedition collected at and near that
latitude specimens of _Cottus quadricornis_, _Icelus hamatus_,
_Cyclopterus spinosus_, _Liparis fabricii_, _Gymnelis viridis_, and
_Gadus fabricii_. This number probably would have been larger if the
difficulties of collecting fishes in those high latitudes were not
almost insuperable for the greater part of the year.

As far as we know, the fishes north and south of Behring’s Straits
belong to the same generic or family types as those of the
corresponding latitudes of the Eastern Hemisphere, though the majority
are specifically distinct. But the information we possess of the fishes
of the northernmost extremity of the Pacific is extremely scanty and
vague. Farther south, whence now and then a collection reaches Europe,
we meet with some European species, as the Herring, Halibut, Hake.

The Chondropterygians are very scarce, and it is doubtful whether
another Chondropterygian, beside the pelagic _Læmargus_ or Greenland
Shark, crosses the Arctic circle. In the more temperate latitudes
of South Greenland, Iceland, and Northern Scandinavia, _Acanthias_,
_Centroscyllium_, and a species of _Raja_, also _Chimæra_, are met with.

Of Acanthopterygians the families of _Cottidæ_, _Cataphracti_,
_Discoboli_, and _Blenniidæ_ are well represented, and several of
the genera are characteristic of the Arctic fauna: marine species
of _Cottus_; _Centridermichthys_, _Icelus_, _Triglops_; _Agonus_,
_Aspidophoroides_; _Anarrhichas_, _Centronotus_, _Stichæus_;
_Cyclopterus_ and _Liparis_. Two species of _Sebastes_ are rather
common.

Characteristic is also the development of Gadoid fishes, of which some
thirteen species, belonging to _Gadus_, _Merluccius_, and _Molva_,
form one of the principal articles of food to the inhabitants of the
coasts of the Arctic Ocean. The Blennioid Anacanthini or _Lycodidæ_,
are limited to the Arctic and Antarctic coasts. _Ammodytes_ and a few
Flat-fishes (_Hippoglossoides_ and _Pleuronectes_) are common in the
more temperate parts.

Labroids only exceptionally penetrate so far towards the north.

Physostomes are very scarce, and represented only by a few species of
_Clupea_ and by _Mallotus_; the latter is an ancient inhabitant of the
Greenland coasts, fossil remains, indistinguishable from the species
of the present day, being frequently found in nodules of clay of
comparatively recent formation.

The Arctic climate is still less favourable to the existence of
Lophobranchs, only a few _Syngnathus_ and _Nerophis_ being present in
the more southern latitudes, to which they have been carried by oceanic
currents from their more congenial home in the south. Scleroderms and
Plectognaths are entirely absent.

The Gadoids are accompanied by _Myxine_, which parasitically thrives in
them.


                   II. THE NORTHERN TEMPERATE ZONE.


          A. _Shore Fishes of the Temperate North Atlantic_.

This part of the fauna may be subdivided into three districts:--

1. The fishes of the north-eastern shores, viz. of the British
islands, of Scandinavia so far as it is not included in the Arctic
fauna, and of the continent of Europe southwards to about 40° of lat.
N.--_British_ district.

2. The fishes of the Mediterranean shores and of the adjoining shores
of the Atlantic, including the Azores, Madeira, and the Canary
Islands--_Mediterranean_ district.

3. The fishes of the western shores, from 60° lat. N. to about 30° lat.
N.--the _North American_ district.

1. The _British_ district shows scarcely any marked distinctive
features; the character of its fauna is simply intermediate between
that of the Arctic Ocean and the Mediterranean district; truly Arctic
forms disappear, while such as are also found in the Mediterranean make
their appearance. Also with regard to the abundance of individuals
and variety of fishes this district forms a transition from the north
towards the south.

Besides the few Arctic Chondropterygians, all of which extend into this
district, the small shore Dog-fishes are well represented (_Mustelus_,
_Galeus_, _Scyllium_, _Pristiurus_); the ubiquitous Rhina or Monk-fish
is common; of Rays, _Raja_ predominates in a variety of species over
_Torpedo_ and _Trygon_, which are still scarce.

Of Acanthopterygians, _Centridermichthys_, _Icelus_, _Triglops_, and
_Aspidophoroides_, do not extend from the north into this district; and
_Cottus_, _Anarrhichas_, _Centronotus_, _Stichæus_, the _Discoboli_
disappear within its limits. Nearly all the remainder are genera which
are also found in the Mediterranean districts. The following are the
principal forms, and known to propagate on these shores: _Labrax_;
_Serranus_, _Polyprion_, _Dentex_; _Mullus_; _Cantharus_, _Pagrus_,
_Pagellus_; _Sebastes_; _Cottus_, _Trigla_, _Agonus_; _Trachinus_;
_Sciæna_ (?); _Zeus_; _Trachurus_, _Capros_; _Callionymus_;
_Discoboli_; _Lophius_; _Anarrhichas_, _Centronotus_, _Stich__æus_;
_Blenniops_, _Zoarces_ (not in Mediterranean); _Cepola_; _Lepadogaster_.

Of the Anacanthini the Gadoids are as numerous as in the Arctic
Ocean, most being common to both districts; they are represented by
_Gadus_, _Gadiculus_, _Merluccius_, _Phycis_, _Molva_, _Motella_,
_Raniceps_, and _Brosmius_; but, whilst the majority show their
northern origin by not extending into the Mediterranean, _Ammodytes_
and most _Pleuronectidæ_ prove themselves to be the more southern
representatives of this order. In the British district we find
_Hippoglossus_, _Hippoglossoides_, _Rhombus_, _Phrynorhombus_,
_Pleuronectes_, _Solea_, and only the two first are not met with in the
Mediterranean.

Labroids are common; with the exception of the North American
_Tautoga_, all the other genera are met with.

Physostomes are not well represented, viz. by one species of _Osmerus_,
one of _Engraulis_, one of _Conger_, and about five of _Clupea_.

_Syngnathus_ and _Nerophis_ become more common as we proceed
southwards; but the existence of Scleroderms and Plectognaths is
indicated by single individuals only, stragglers from their southern
home, and unable to establish themselves in a climate ungenial to them.

The Gadoids are accompanied by _Myxine_; and _Branchiostoma_ may be
found in all suitable localities.

2. The _Mediterranean_ district is distinguished by a great variety of
forms; yet, with the exception of a few genera established for single
species, none of the forms can be considered peculiar to it; and even
that small number of peculiar genera is more and more diminished as
our knowledge of the distribution of fishes advances. Some genera are
identical with those found on the western coasts of the Atlantic and in
the West Indies; but a most remarkable and unexpected affinity obtains
with another very distant fauna, viz. that of Japan. The number of
genera common to the Mediterranean district and the Japanese coasts
is larger than that of the genera common to the Mediterranean and the
opposite American coasts.

The Chondropterygians found in the British district continue in the
Mediterranean, their number being increased by _Centrina_, _Spinax_,
_Pteroplatea_, and some species of _Rhinobatus_, a genus more
numerously represented in the Tropics. _Torpedo_ and _Trygon_ are
common.

The greatest variety belong to the Acanthopterygians, as will be seen
from the following list:--_Labrax_; _Anthias_, _Serranus_, _Polyprion_,
_Apogon_, _Pomatomus_, _Pristipoma_, _Diagramma_ (an Indian genus
with two Mediterranean species, and otherwise not represented in the
Atlantic), _Dentex_, _Mæna_, _Smaris_; _Mullus_; _Cantharus_, _Box_,
_Scatharxs_, _Oblata_, _Sargus_, _Pagrus_, _Pagellus_, _Chrysophrys_;
_Sebastes_, _Scorpæna_; _Hoplostethus_, _Beryx_, _Polymixia_; _Trigla_,
_Lepidotrigla_, _Agonus_, _Peristethus_; _Trachinus_, _Uranoscopus_;
_Umbrina_, _Sciæna_; _Sphyræna_; _Aphanopus_, _Lepidopus_,
_Nesiarchus_, _Trichiurus_, _Thyrsites_; _Cubiceps_; _Zeus_, _Cyttus_;
_Stromateus_; _Trachurus_, _Caranx_, _Capros_, _Diretmus_, _Antigonia_;
_Callionymus_; _Batrachus_; _Lophius_; _Cristiceps_, _Tripterygium_;
_Cepola_; _Lepadogaster_; _Centriscus_; _Notacanthus_.

The _Labridæ_ are as common as, or even more so than, in the British
district, and represented by the same genera. But, besides, some
other Pharyngognaths, properly belonging to the Tropical Atlantic,
have fully established themselves, though only by a few species, viz.
_Glyphidodon_ and _Heliastes_; _Cossyphus_, _Novacula_, _Julis_,
_Coris_, and _Scarus_.

The Gadoids show a marked decrease of development; and the species of
_Gadus_, _Gadiculus_, _Mora_, _Strinsia_, _Phycis_, and _Molva_, which
are peculiar to the Mediterranean, seem to inhabit rather the colder
water of moderate depths, than the surface near the shore. _Motella_,
however, proves to be a true Shore fish also in the Mediterranean,
at least in its adult state. _Ophidium_ and _Fierasfer_ appear now
besides _Ammodytes_. As the Gadoids decrease, so the _Pleuronectidæ_
increase, the genera of the Mediterranean district being _Rhombus_,
_Phrynorhombus_, _Arnoglossus_, _Citharus_, _Rhomboidichthys_,
_Pleuronectes_ (a northern genus not extending farther southwards),
_Solea_, _Synaptura_, and _Ammopleurops_.

The variety of Physostomes is small; the following only being
superadded to those of the British district:--_Saurus_ (a tropical
genus), _Aulopus_; _Congromuræna_, _Heteroconger_, _Myrus_,
_Ophichthys_, _Muræna_.

The Lophobranchs are more numerous in species and individuals than in
the British district; and, besides _Syngnathus_ and _Nerophis_, several
species of _Hippocampus_ are common. Also a few species of _Balistes_
occur.

_Myxine_ is lost in this district; whilst _Branchiostoma_ is abundant.

3. The shore fishes of the _North American_ district consist, as on
the eastern coasts of the North Atlantic, of northern and southern
elements; but they are still more mixed with each other than on the
European coasts, so that a boundary line cannot be drawn between
them. The affinity to the fauna of the eastern shores is great,
but almost entirely limited to the genera composing the fauna of
the British district. British genera not found on the American
coasts are--_Galeus_, _Scyllium_, _Chimæra_, _Mullus_, _Pagellus_,
_Trigla_, _Trachinus_, _Zeus_, _Callionymus_. The southern elements
of North America are rather derived from the West Indies, and
have no special affinity to Mediterranean forms; very few of the
non-British Mediterranean forms extend across the Atlantic; instead
of a Mediterranean we find a West Indian element. Many of the British
_species_ range across the Atlantic, and inhabit in an unchanged
condition the northern parts of this district; and from the frequent
occurrence of isolated specimens of other British species on the North
American coast, we may presume that many more occasionally cross the
Atlantic, but without being able to obtain a permanent footing.

The genera peculiar to this district are few in number, and composed
of very few species, viz. _Hemitripterus_, _Pammelas_, _Chasmodes_,
_Cryptacanthodes_, and _Tautoga_.

The close resemblance of what must be considered northern forms to
those of Europe will be evident from the following list:--

_Mustelus, Rhina, Torpedo, Raja, Trygon._

_Labrax, Centropristis, Serranus; Pagrus, Chrysophrys; Sebastes,
Hemitripterus; Cottus, Aspidophoroides; Uranoscopus; Micropogon,
Pogonias, Sciæna; Trachurus, Pammelas; Cyclopterus, Liparis; Lophius;
Anarrhichas, Chasmodes, Stichcæus, Centronotus, Cryptacanthodes,
Zoarces._

_Tautoga, Ctenolabrus._

_Gadus, Merluccius, Phycis, Molva, Motella, Brosmius; Ophidium_ (one
species, perhaps identical with a Mediterranean species); _Ammodytes;
Hippoglossus, Hippoglossoides, Rhombus, Pleuronectes_.

_Osmerus, Mallotus; Engraulis, Clupea; Conger._

_Syngnathus--Myxine--Branchiostoma._

West Indian genera, or at least genera which are more developed within
the tropics, and which extend more or less northwards in the North
American district, are:--

_Pteroplatea_ (also in the Mediterranean).

_Gerres, Dules (auriga), Lobotes, Ephippus; Sargus; Prionotus; Umbrina,
Otolithus, Larimus; Sphyræna_ (Mediterr.); _Trichiurus_ (Mediterr.);
_Elacate; Cybium, Trachynotus; Stromateus_ (Mediterr.); _Caranx_;
_Batrachus_ (Mediterr.); _Malthe_.

_Pseudorhombus_, _Solea_ (Mediterr.)

_Saurus_ (Mediterr.); _Etrumeus, Albula, Elops, Megalops_.

_Hippocampus_ (Mediterr.)

_Balistes, Monacanthus._


            B. SHORE FISHES OF THE TEMPERATE NORTH PACIFIC.

This fauna shows a great affinity to that of the temperate North
Atlantic, not only in including a considerable proportion of identical
genera, and even of species, but also in having its constituent parts
similarly distributed. However, our knowledge of the ichthyology of
this fauna is by no means complete. Very few collections have been
made in Northern Japan, and on the coasts farther north of it; and,
again, the ichthyology of the coasts of Southern California is but
little known. Southern Japan has been well searched, but very little
attention has been paid to the extent of the northward range of the
species. In collections made by Mr. Swinhoe at Chefoo, in lat. 37° N.,
the proportions of temperate and tropical fishes were found to be about
equal. Thus, the details of the distribution of the fishes of these
shores have still to be worked out; nevertheless, three divisions may
be recognised which, for the present, may be defined as follows:--

1. The fishes of the north-western shores, to about 37° lat. N.,
including the corresponding northern parts of Japan--_Kamtschatkan_
district; this corresponds to the British district of the Atlantic.

2. The fishes of Southern Japan and the corresponding shores of the
continent of Asia, between 37° and 30° lat. N.--_Japanese_ district,
which corresponds to the Mediterranean.

3. The fishes of the eastern shores southwards to the latitude of
San Francisco--_Californian_ district; this corresponds to the North
American district of the Atlantic.

Too little is known of the shore fishes of the coasts between San
Francisco and the tropic to enable us to treat of it as a separate
division.

The Shore fishes of the North Pacific generally are composed of the
following elements:--

_a._ Arctic forms which extend into the Arctic Ocean, and the majority
of which are also found in the British district.

_b._ Peculiar forms limited to the North Pacific, like the
_Heterolepidina_, _Embiotocidæ_, and certain Cottoid and Blennioid
genera.

_c._ Forms identical with fishes of the Mediterranean.

_d._ Peculiar forms limited to the southern parts of Japan.

_e._ Tropical forms which have entered the North Pacific from the
south.

       *       *       *       *       *

1. The small list of fishes which we can assign to the _Kamtschatkan_
district is due rather to the imperfect manner in which its fauna has
been explored than to its actual poverty of fishes; thus, although we
may be sure that sooner or later the small kinds of Dog-fishes of the
British district will be found there also, at present we have positive
knowledge of the occurrence of only two Chondropterygians, viz.
_Chimæra_ and _Raja_. The species of the latter genus seem to be much
less numerous than in the Atlantic.

Of Acanthopterygians the following are known:--_Sebastes_; _Chirus_,
_Agrammus_; _Podabrus_, _Blepsias_, _Cottus_, _Centridermichthys_,
_Hemilepidotus_, _Agonus_; _Trichodon_; _Callionymus_; _Liparis_;
_Dictyosoma_, _Stichæus_, _Centronotus_.

Labroids are absent; they are clearly a type unable to endure great
cold; of the Embiotocoids which represent them in the Pacific, one
species only (a species of _Ditrema_) is known from this district.

The Gadoids are, so far as we know at present, sparsely represented,
viz. by isolated species of _Gadus_, _Motella_, and _Lotella_, the
latter being an inhabitant of moderate depths rather than of the
surface. _Hippoglossus_, _Pleuronectes_, and _Parophrys_, seem to occur
everywhere at suitable localities.

The Physostomes are nearly the same as in the British district, viz. a
Smelt (_Hypomesus_), probably also the Arctic _Mallotus_, an Anchovy,
several species of _Clupea_, and the Conger-eel. A very singular
Salmonoid fish, _Salanx_, which is limited to the north-western
Pacific, occurs in great abundance.

Also, the Lophobranchs correspond in their development to those of the
British district, _Nerophis_ being replaced by _Urocampus_.

Neither Myxinoids nor _Branchiostoma_ have as yet been found.

2. The _Japanese_ district is, like the Mediterranean, distinguished
by a great variety of forms; some of them are peculiar to it (marked
_J._ in the following list); others occur in the Mediterranean, though
also in other districts (_M._) The resemblance to the Mediterranean
is even greater than would appear from the following list of genera,
inasmuch as a considerable number of species are identical in both
districts. Three of the Berycoid genera have hitherto been found in
the Japanese and Mediterranean districts only, and nowhere else.
Another very singular fact is that some of the most characteristic
genera, like _Mullus_, _Zeus_, _Callionymus_, _Centriscus_, inhabit
the Mediterranean and Japanese districts, _but have never reached the
opposite American coasts, either in the Atlantic or Pacific_; although,
at least in the latter, the oceanic currents would rather favour
than obstruct their dispersal in the direction towards America. Bold
as the hypothesis may appear, we can only account for the singular
distribution of these shore fishes by assuming that the Mediterranean
and Japanese seas were in direct and open communication with each other
within the period of the existence of the present Teleosteous Fauna.

Gadoids have disappeared, or are represented by forms inhabiting
moderate depths. Neither Myxine nor _Branchiostoma_ are known to have
as yet been found.


                   _List of Japanese Shore Fishes._

_Chimæra_ (M.)

_Galeus_ (M.), _Mustelus_ (M.), _Triacis_, _Scyllium_ (M.),
_Crossorhinus_, _Pristiophorus_, _Cestracion_; _Rhina_ (M.);
_Rhinobatus_ (M.), _Narcine_, _Raja_ (M.), _Trygon_ (M.), _Pteroplatea_
(M.)

_Percalabrax_ (J.), _Niphon_ (J.), _Centropristis_, _Anthias_ (M.),
_Serranus_ (M.), _Apogon_ (M.), _Scombrops_ (J.), _Acropoma_, _Anoplus_
(J.), _Pristipoma_ (M.), _Hapalogenys_ (J.), _Histiopterus_, _Velifer_
(J.), _Dentex_ (M.), _Erythrichthys_--_Mullidæ_ (M.)--_Girella_,
_Pagrus_ (M.), _Chrysophrys_ (M.)--_Chilodactylus_--_Sebastes_
(M.), _Scorpæna_ (M.), _Aploactis_, _Trichopleura_,
_Pelor_--_Monocentris_ (J.), _Hoplostethus_ (M.), _Beryx_ (M.),
_Polymixia_ (M.)--_Platycephalus_, _Hoplichthys_ (J.), _Bembras_
(J.), _Prionotus_, _Lepidotrigla_ (M.), _Trigla_ (M.), _Peristethus_
(M.)--_Uranoscopus_ (M.), _Percis_, _Sillago_, _Latilus_.--_Sciæna_
(M.), _Otolithus_--_Sphyræna_ (M.)--_Lepidopus_ (M.), _Trichiurus_
(M.)--_Zeus_ (M.)--_Caranx_, _Trachurus_ (M.)--_Callionymus_
(M.)--_Lophius_ (M.), _Halieuthæa_ (J.)--_Hoplognathus_--_Cepola_
(M.)--_Centriscus_ (M.), _Fistularia_.

_Heliastes_ (M.)--_Labrichthys_, _Duymæria_, _Platyglossus_, _Novacula_
(M.), _Julis_ (M.), _Coris_ (M.)

_Sirembo_ (J.)--_Motella_ (M.)--_Ateleopus_ (J.)

_Pseudorhombus_, _Pleuronectes_ (M.), _Solea_ (M.), _Synaptura_ (M.)

_Saurus_ (M.), _Harpodon_.--_Salanx_ (J.)--_Engraulis_ (M.), _Clupea_
(M.), _Etrumeus_--_Conger_ (M.), _Congromuræna_ (M.), _Murænesox_ (M.),
_Oxyconger_, _Myrus_ (M.), _Ophichthys_ (M.), _Muræna_ (M.)

_Syngnathus_ (M.), _Hippocampus_ (M.), _Solenognathus_.

_Triacanthus_, _Monacanthus_, _Ostracion_.

3. The _Californian_ district includes a marked northern element, the
principal constituents of which are identical with types occurring in
the corresponding district of the Atlantic, viz. the North American,
as exemplified by _Discoboli_, _Anarrhichas_, _Centronotus_, _Cottus_,
_Hippoglossus_, _Clupea_ (_harengus_), etc. But it possesses also,
in the greatest degree of development, some types almost peculiar
to itself, as the _Heterolepidina_, some remarkable Cottoid and
Blennioid genera, and more especially the Embiotocoids--viviparous
Pharyngognaths--which replace the Labroids of the other hemisphere.
Gadoids are much less numerous than in the North American district. The
southern forms are but little known, but it may be anticipated that,
owing to the partial identity of the Faunæ of the two coasts of the
Isthmus of Panama, a fair proportion of West Indian forms will be found
to have entered this district from the south. The following are the
principal genera:--

_Chimœra_, _Galeus_, _Mustelus_, _Triacis_, _Cestracion_, _Rhina_,
_Raja_.

_Serranus_; _Chirus_, _Ophiodon_, _Zaniolepis_; _Sebastes_;
_Nautichthys_, _Scorpœnichthys_, _Cottus_, _Centridermichthys_,
_Hemilepidotus_, _Artedius_, _Prionotus_, _Agonus_; _Cyclopterus_,
_Liparis_; _Anarrhichas_, _Neoclinus_, _Cebidichthys_, _Stichœus_,
_Centronotus_, _Apodichthys_; _Psychrolutes_; _Auliscops_.

_Embiotocidœ_.

_Gadus_. _Hippoglossus_, _Psettichthys_, _Citharichthys_,
_Paralichthys_, _Pleuronectes_, _Parophrys_.

_Osmerus_, _Thaleichthys_, _Hypomesus_; _Engraulis_, _Clupea_.

_Syngnathus_.


                      III.--THE EQUATORIAL ZONE.

As we approach the Tropic from the north, the tribes characteristic
of the Arctic and Temperate zones become scarcer, and disappear
altogether: to be replaced by the greater variety of Tropical types.
Of Chondropterygians, the _Chimœridœ_, _Spinacidœ_, _Mustelus_, and
_Raja_, do not pass the Tropic, or appear in single species only;
and of Teleosteans, the _Berycidæ_, _Pagrus_, the _Heterolepidina_,
_Cottus_ and allied genera, _Lophius_, _Anarrhichas_, _Stichæus_,
_Lepadogaster_, _Psychrolutes_, _Centriscus_, _Notacanthus_, the
_Labridæ_ and _Embiotocidæ_, the _Lycodidæ_, _Gadidæ_, and marine
_Salmonidæ_ disappear either entirely, or retire from the shores and
surface into the depths of the ocean.

With regard to variety of forms, as well as to number of individuals,
this zone far surpasses either of the temperate zones; in this
respect, the life in the sea is as that on the land. Coast fishes
are not confined to the actual coast-line, but abound on the
coral reefs, with which some parts of the Atlantic and Pacific
are studded, and many of which are submerged below the water. The
abundance of animal and vegetable life which flourishes on them
renders them the favourite pasture-grounds for the endless variety of
coral-fishes (_Squamipinnes_, _Acronuridæ_, _Pomacentridæ_, _Julidæ_,
_Plectognathi_, etc.), and for the larger predatory kinds. The colours
and grotesque forms of the Fishes of the Tropics have justly excited
the admiration of the earliest observers. Scarlet, black, blue, pink,
red, yellow, etc., are arranged in patterns of the most bizarre
fashion, mingling in spots, lines, bands; and reminding us of the words
of Captain Cook when describing the coral-reefs of Palmerston Island:
“The glowing appearance of the Mollusks was still inferior to that of
the multitude of fishes that glided gently along, seemingly with the
most perfect security. The colours of the different sorts were the most
beautiful that can be imagined--the yellow, blue, red, black, etc., far
exceeding anything that art can produce. Their various forms, also,
contributed to increase the richness of this sub-marine grotto, which
could not be surveyed without a pleasing transport.”

Of Chondropterygians the _Scylliidæ_, _Pristis_ (Saw-fishes),
_Rhinobatidæ_, and _Trygonidæ_ attain to the greatest development.
Of Acanthopterygians _Centropristis_, _Serranus_, _Plectropoma_,
_Mesoprion_, _Priacanthus_, _Apogon_, _Pristipoma_, _Hæmulon_,
_Diagramma_, _Gerres_, _Scolopsis_, _Synagris_, _Cæsio_, _Mullidæ_,
_Lethrinus_, _Squamipinnes_, _Cirrhites_, some genera of _Scorpænidæ_,
_Platycephalus_, _Sciænidæ_, _Sphyræna_, _Caranx_ _Equula_,
_Callionymus_, _Teuthis_, _Acanthurus_, _Naseus_, are represented by
numerous species; and the majority of these genera and families are
limited to this zone. Of Pharyngognaths the _Pomacentridæ_, _Julidina_,
and _Scarina_, are met with near every coral formation in a living
condition. Of Gadoids, a singular minute form, _Bregmaceros_, is almost
the only representative, the other forms belonging to deep water, and
rarely ascending to the surface. Flat-fishes (_Pleuronectidæ_) are
common on sandy coasts, and the majority of the genera are peculiar
to the Tropics. Of _Physostomi_ only the _Saurina_, _Clupeidæ_, and
_Murænidæ_ are represented, the _Clupeidæ_ being exceedingly numerous
in individuals, whilst the _Murænidæ_ live more isolated, but show a
still greater variety of species. Lophobranchii and Sclerodermi are
generally distributed. Branchiostoma has been found on several coasts.

Geographically it is convenient to describe the Coast fauna of the
tropical Atlantic separately from that of the Indo-Pacific ocean. The
differences between them, however, are far less numerous and important
than between the freshwater or terrestrial faunæ of continental
regions. The majority of the principal types are found in both, many of
the species being even identical; but the species are far more abundant
in the Indo-Pacific than in the Atlantic, owing to the greater extent
of the archipelagoes in the former. But for the broken and varied
character of the coasts of the West Indies, the shores of the tropical
Atlantic would, by their general uniformity, afford but a limited
variety of conditions to the development of specific and generic
forms, whilst the deep inlets of the Indian ocean, with the varying
configuration of their coasts, and the different nature of their
bottom, its long peninsulas, and its archipelagoes, and the scattered
islands of the tropical Pacific, render this part of the globe the
most perfect for the development of fish-life. The fishes of the
Indian and Pacific oceans (between the Tropics) are almost identical,
and the number of species ranging from the Red Sea and east coast of
Africa to Polynesia, even to its westernmost islands, is very great
indeed. However, this Indo-Pacific fauna does not reach the Pacific
coast of South America. The wide space devoid of islands, east of the
Sandwich Islands and the Marquesas group, together with the current
of cold water which sweeps northwards along the South American coast,
has proved to be a very effectual barrier to the eastward extension
of the Indo-Pacific fauna of coast fishes; and, consequently, we find
an assemblage of fishes on the American coast and at the Galapagoes
Islands, sufficiently distinct to constitute a distinct zoological
division.

The following list, which contains only the principal genera and groups
of coast fishes, will give an idea of the affinity of the tropical
Atlantic and Indo-Pacific:--[28]

                                    Trop.-Atl.  Indo-Pac.

    Scylliidæ                           --         13
    _Pristis_                            3          4
    _Rhinobatidæ_                        4          8
    _Torpedinidæ_                        1          8
    _Trygonidæ_                         14         24
    _Etelis_                             1          1
    _Aprion_                            --          1
    _Apsilus_                            1         --
    _Centropristis_                     15         --
    _Anthias_                            4          5
    _Serranus_                          30         85
    _Plectropoma_                       11          5
    _Grammistes_                        --          2
    _Rhypticus_                         3          --
    _Diploprion_                       --           1
    _Myriodon_                         --           1
    _Mesoprion_                        15          50
    _Priacanthus_                       4          12
    _Apogon_ and _Chilodipterus_        2          75
    _Pristipoma_                       12          14
    _Hæmulon_                          15          --
    _Diagramma_                        --          30
    _Gerres_                           12          16
    _Scolopsis_                        --          20
    Dentex and _Symphorus_             --           7
    _Synagris_ and _Pentapus_          --          24
    _Cæsio_                            --          12
    Mullidæ                             5          22
    Sargus                              7           2
    _Lethrinus_                         1          18
    _Chrysophrys_                       1           7
    _Pimelepterus_                      1           5
    _Squamipinnes_                     13         110
    _Toxotes_                          --           2
    _Cirrhites_                        --          20
    Scorpænidæ                          2          65
    _Myripristis_                       3          15
    _Holocentrum_                       6          25
    _Platycephalus_                    --          25
    Prionotus                           1          --
    Trigla                             --           4
    Peristethus                         2           6
    Uranoscopina                        2           8
    _Champsodon_                       --           1
    _Percis_                           --          10
    _Sillago_                          --           5
    Latilus                             1           2
    _Opisthognathus_                    2           5
    _Pseudochromis_                    --           8
    _Cichlops_ and _Pseudoplesiops_    --           2
    _Sciænidæ_                         44          43
    _Sphyræna_                          1          10
    _Trichiuridæ_                       6           5
    _Caranx_                           20          60
    _Chorinemus_                        4           7
    _Trachynotus_                       6           4
    _Psettus_                           1           2
    _Platax_                           --           7
    _Zanclus_                          --           1
    _Equula_ and _Gazza_               --          20
    _Teuthis_                          --          30
    _Acanthurus_                        3          42
    _Naseus_                           --          12
    _Kurtidæ_                           1           6
    _Gobiodon_                         --           7
    Callionymus                        --          17
    _Batrachidæ_                        5           4
    _Tetrabrachium_                    --           1
    Malthe                              1          --
    _Petroscirtes_                     --          30
    Clinus                              6          --
    _Dactyloscopus_                     1          --
    _Malacanthus_                       1           2
    Cepola                             --           1
    Gobiesocidæ                         5           1
    _Amphisile_                        --           3
    _Fistulariidæ_                      3           3
    _Pomacentridæ_                     17         120
    _Lachnolæmus_                       1          --
    _Julidina_                         36         190
    Pseudodax                          --           1
    _Scarina_                          21          65
    Pseudophycis                       --           1
    _Bregmaceros_                      --           1
    Ophidiidæ                           3           7
    _Fierasfer_                        --           6
    Pleuronectidæ                      21          56
    _Saurina_                           5           9
    Clupeidæ.                          33          84
    _Chirocentrus_                     --           1
    _Murænidæ_                         47         130
    _Pegasus_                          --           3
    _Solenostoma_                      --           2
    Syngnathidæ                         7          41
    _Sclerodermi_                      16          67
    Gymnodontes                        23          40


              A. _Shore Fishes of the Tropical Atlantic._

The boundaries of the tropical Atlantic extend zoologically a few
degrees beyond the Northern and Southern Tropics, but as the mixture
with the types of the temperate zone is very gradual, no distinct
boundary line can be drawn between the tropical and temperate faunæ.

Types, almost exclusively limited to it, and not found in the
Indo-Pacific, are few in number, as _Centropristis_, _Rhypticus_,
_Hæmulon_, _Malthe_. A few others preponderate with regard to the
number of species, as _Plectropoma_, _Sargus_, _Trachynotus_,
_Batrachidæ_, and _Gobiesocidæ_. The Sciænoids are equally represented
in both oceans. All the remainder are found in both; but in the
minority in the Atlantic, where they are sometimes represented by one
or two species only (for instance, _Lethrinus_).


         B. _Shore Fishes of the Tropical Indo-Pacific Ocean._

The ichthyological boundaries of this part of the tropical zone may be
approximately given as 30° of lat. N. and S.; on the Australian coasts
it should probably be placed still farther south, viz., to 34°; it
includes, as mentioned above, the Sandwich Islands, and all the islands
of the South Sea, but not the American coasts.

Some eighty genera of Shore fishes are peculiar to the Indo-Pacific,
but the majority consists of one or a few species only; comparatively
few have a plurality of species, as _Diagramma_, _Lethrinus_, _Equula_,
_Teuthis_, _Amphiprion_, _Dascyllus_, _Choerops_, _Chilinus_,
_Anampses_, _Stethojulis_, _Coris_, _Coilia_.

The Sea-perches, large and small, which feed on Crustaceans and other
small fishes, and the coral-feeding Pharyngognaths are the types which
show the greatest generic and specific variety in the Indo-Pacific.
Then follow the _Squamipinnes_ and _Murænidæ_, the _Clupeidæ_ and
_Carangidæ_ families in which the variety is more that of species than
of genus. The _Scorpænidæ_, _Pleuronectidæ_, _Acronuridæ_, _Sciænidæ_,
_Syngnathidæ_, and _Teuthyes_, are those which contribute the next
largest contingents. Of shore-loving Chondropterygians the _Scylliidæ_
and _Trygonidæ_ only are represented in moderate numbers, though they
are more numerous in this ocean than in any other.


     C. _Shore Fishes of the Pacific Coasts of Tropical America_.

As boundaries within which this fauna is comprised, may be indicated
30° lat. N. and S., as in the Indo-Pacific. Its distinction from the
Indo-Pacific lies in the almost entire absence of coral-feeding fishes.
There are scarcely any Squamipinnes, Pharyngognaths or Acronuridæ,
and the Teuthyes are entirely absent. The genera that remain are such
as are found in the tropical zone generally, but the species are
entirely different from those of the Indo-Pacific. They are mixed with
a sprinkling of peculiar genera, consisting of one or two species,
like _Discopyge_, _Hoplopagrus_, _Doydixodon_, but they are too few in
number to give a strikingly peculiar character to this fauna.

The Three districts are distinguishable:--

a. _Central American district_, in which we include, for the present,
Lower California, shows so near an affinity to the tropical Atlantic
that, if it were not separated from it by the neck of land uniting
the two American Continents, it would most assuredly be regarded as
a portion of the Fauna of the tropical Atlantic. With scarcely any
exceptions the genera are identical, and of the species found on the
Pacific side nearly one-half have proved to be the same as those of the
Atlantic. The explanation of this fact has been found in the existence
of communications between the two oceans by channels and straits
which must have been open till within a recent period. The isthmus of
Central America was then partially submerged, and appeared as a chain
of islands similar to that of the Antilles; but as the reef-building
corals flourished chiefly north and east of those islands, and were
absent south and west of them, reef-fishes were excluded from the
Pacific shores when the communications were destroyed by the upheaval
of the land.

_b_. The _Galapagoes district_ received its coast fauna principally
from the Central American district, a part of the species being
absolutely the same as on the coast of the Isthmus of Panama, or as
in the West Indies. Yet the isolation of this group has continued
a sufficiently long period to allow of the development of a number
of distinct species of either peculiarly Atlantic genera (such as
_Centropristis_, _Rhypticus_, _Gobiesox_, _Prionotus_), or at least
tropical genera (such as _Chrysophrys_, _Pristipoma_, _Holacanthus_,
_Caranx_, _Balistes_). A few other types from the Peruvian coast
(_Doydixodon_), or even from Japan (_Prionurus_), have established
themselves in this group of islands. A species of _Cestracion_ has also
reached the Galapagoes, but whether from the south, north, or west,
cannot be determined.

The presence of the Atlantic fauna on the Pacific side is felt still
farther west than the Galapagoes, some Atlantic species having
reached the Sandwich Islands, as _Chætodon humeralis_ and _Blennius
brevipinnis_.

c. The _Peruvian district_ possesses a very limited variety of
shore fishes, which belong, with few exceptions, like _Discopyge_,
_Hoplognathus_, _Doydixodon_, to genera distributed throughout the
tropical zone, or even beyond it. But the species, so far as they are
known at present, are distinct from those of the Indo-Pacific, as well
as of the tropical Atlantic; and therefore this district cannot be
joined either to the Central American or the Galapagoes.


                   IV.--THE SOUTHERN TEMPERATE ZONE.

This zone includes the coasts of the southern extremity of Africa, from
about 30° lat. S., of the south of Australia with Tasmania, of New
Zealand, and the Pacific and Atlantic coasts of South America between
30° and 50° lat. S.

The most striking character of this fauna is the reappearance
of types inhabiting the corresponding latitudes of the Northern
Hemisphere, and not found in the intervening tropical zone. This
interruption of the continuity in the geographical distribution
of Shore-fishes is exemplified by species as well as genera, for
instance--_Chimæra monstrosa_, _Galeus canis_, _Acanthias vulgaris_,
_Acanthias blainvillii_, _Rhina squatina_, _Zeus faber_, _Lophius
piscatorius_, _Centriscus scolopax_, _Engraulis encrasicholus_,
_Clupea sprattus_, _Conger vulgaris_. Instances of genera are still
more numerous--_Cestracion_, _Spinax_, _Pristiophorus_, _Raja_;
_Callanthias_, _Polyprion_, _Histiopterus_, _Cantharus_, _Box_,
_Girella_, _Pagellus_, _Chilodactylus_, _Sebastes_, _Aploactis_,
_Agonus_, _Lepidopus_, _Cyttus_, _Psychrolutidæ_, _Notacanthus_;
_Lycodes_, _Merluccius_, _Lotella_, _Phycis_, _Motella_; _Aulopus_;
_Urocampus_, _Solenognathus_; _Myxine_.

Naturally, where the coasts of the tropical zone are continuous with
those of the temperate, a number of tropical genera enter the latter,
and genera which we have found between the tropics as well as in the
temperate zone of the Northern Hemisphere, extend in a similar manner
towards the south. But the truly tropical forms are absent; there
are no _Squamipinnes_, scarcely any _Mullidæ_, no _Acronuri_, no
_Teuthyes_, no _Pomacentridæ_ (with a single exception on the coast of
Chili), only one genus of _Julidina_, no _Scarina_, which are replaced
by another group of Pharyngognaths, the _Odacina_. The _Labrina_,
so characteristic of the temperate zone of the Northern Hemisphere,
reappear in a distinct genus (_Malacopterus_) on the coast of Juan
Fernandez.

The family of _Berycidæ_, equally interesting with regard to their
distribution in time and in space, consists of temperate and tropical
genera. The genus by which this family is represented in the southern
temperate zone (_Trachichthys_) is much more nearly allied to the
northern than to the tropical genera.

The true _Cottina_ and _Heterolepidina_ (forms with a bony stay of the
præoperculum, which is generally armed) have not crossed the tropical
zone; they are replaced by fishes extremely similar in general form,
and having the same habits, but lacking that osteological peculiarity.
Their southern analogues belong chiefly to the family _Trachinidæ_, and
are types of genera peculiar to the Southern Hemisphere.

The _Discoboli_ of the Northern Hemisphere have likewise not penetrated
to the south, where they are represented by _Gobiesocidæ_. These two
families replace each other in their distribution over the globe.

Nearly all the _Pleuronectidæ_ (but they are not numerous) belong to
distinct genera, some, however, being remarkably similar in general
form to the northern _Pleuronectes_.

With Gadoids _Myxinidæ_ reappear, one species being extremely similar
to the European Myxine. _Bdellostoma_ is a genus peculiar to the
southern temperate zone.

As in the northern temperate zone, so in the southern, the number of
individuals and the variety of forms is much less than between the
tropics. This is especially apparent on comparing the numbers of
species constituting a genus. In this zone genera composed of more than
ten species are the exception, the majority having only from one to
five.

The proportion of genera limited to this zone is rather high; they
will be indicated under the several districts, which we distinguish on
geographical rather than zoological grounds.

1. The _Cape of Good Hope_ district.

The principal genera found in this district are the following (those
limited to the entire zone being marked with a single (*) and those
peculiar to this district with a double (**) asterisk):--

_Chimæra_, *_Callorhynchus_, _Galeus_, **_Leptocarcharias_, _Scyllium_,
_Acanthias_, _Rhinobatus_, _Torpedo_, _Narcine_, _Astrape_, _Raja_.

_Serranus_, _Dentex_, _Pristipoma_; _Cantharus_, _Box_, **_Dipterodon_,
_Sagrus_, _Pagrus_, _Pagellus_, _Chrysophrys_; *_Chilodactylus_;
_Sebastes_, *_Agriopus_; _Trigla_; _Sphyræna_; _Lepidopus_,
_Thyrsites_; _Zeus_; _Caranx_; _Lophius_; _Clinus_ (10 species),
_Cristiceps_; **_Chorisochismus_.

*_Halidesmus_, *_Genypterus_, _Motella_.

_Syngnathus_.--*_Bdellostoma_.

This list contains many northern forms, which in conjunction with
the peculiarly southern types (_Callorhynchus_, _Chilodactylus_,
_Agriopus_, _Clinus_, _Genypterus_, _Bdellostoma_) leave no doubt
that this district belongs to the southern temperate zone, whilst the
Freshwater fishes of South Africa are members of the tropical fauna.
Only a few (_Rhinobatus_, _Narcine_, _Astrape_, and _Sphyræna_) have
entered from the neighbouring tropical coasts. The development of
Sparoids is greater than in any of the other districts of this zone,
and may be regarded as one of its distinguishing features.

2. The _South Australian_ district comprises the southern coasts of
Australia (northwards, about to the latitude of Sydney), Tasmania,
and New Zealand. It is the richest in the southern temperate zone,
partly in consequence of a considerable influx of tropical forms on the
eastern coast of Australia, where they penetrate farther southwards
than should have been expected from merely geographical considerations;
partly in consequence of the thorough manner in which the ichthyology
of New South Wales and New Zealand has been explored. On the other
hand, the western half of the south coast of Australia is still almost
a _terra incognita_.

The shore-fishes of New Zealand are not so distinct from those of
south-eastern Australia as to deserve to be placed in a separate
district. Beside the genera which enter this zone from the Tropics,
and which are more numerous on the Australian coast than on that of
New Zealand, and beside a few very local genera, the remainder are
identical. Many of the South Australian species, besides, are found
also on the coasts of New Zealand. The principal points of difference
are the extraordinary development of Monacanthus on the coast of South
Australia, and the apparently total absence in Australia of Gadoids,
which in the New Zealand Fauna are represented by six genera.


_Shore-fishes of the South Australian district._


                                       South Australia
                                        and Tasmania.      New Zealand.
    *Callorhynchus (antarcticus).             1                1
    Galeus (canis)                            1                1
    Scyllium  ...                             2                1
    **Parascyllium                            1               --
    Crossorhinus                              1               --
    Cestracion ...                            2                1
    Mustelus (antarcticus)                    1                1
    Acanthias (vulgaris and blainvillii)      2                1
    Rhina                                     1               --
    Pristiophorus                             1               --
    **Trygonorhina (fasciata)                 1                1
      Rhinobatus                              1                1
      Torpedo                                --                1
      Narcine                                 1               --
      Raja                                    3                1
      Trygon (Urolophus)                      3                2
    **Enoplosus                               1               --
      Anthias (richardsonii)                  1                1
      Callanthias                             1               --
      Serranus                                x[29]           --
      Plectropoma                             4               --
    **Lanioperca                              1               --
    **Arripis                                 3                1
      Histiopterus                            1               --
      Erythrichthys                          --                1
     *Haplodactylus                           2                2
      Girella                                 4               --
    **Tephræops                               1               --
      Pagrus                                  1                1
     *Scorpis                                 2                1
    **Atypichthys                             1               --
    **Trachichthys                           --                1
    **Chironemus                              1                1
    **Holoxenus                               1               --
      Chilodactylus                           9                4
    **Nemadactylus                            1               --
    **Latris                                  2                2
      Scorpæna                                4                2
    **Glyptauchen                             1               --
      Centropogon                             2               --
     *Agriopus                                1                1
     *Aploactis                               1               --
    **Pentaroge                               1               --
      Platycephalus                           5               --
      Lepidotrigla                            3                1
      Trigla                                  3                1
    Anema                                     --               1
    **Crapatalus                              --               1
    **Kathetostoma                            1                2
    **Leptoscopus                             1                3
      Percis                                  2                1
     *Aphritis                                1               --
      Sillago                                 2               --
     *Bovichthys                              1                1
     *Notothenia                              --               1
      Sphyræna                                1               --
      Lepidopus                               --               1
      Trichiurus                              1               --
      Thyrsites                               1                1
    **Platystethus                           --                2
      Zeus (faber)                            1                1
      Cyttus                                  1                1
      Trachurus (trachurus)                   1                1
      Caranx                                  x                2
     *Seriolella                             --                1
      Pempheris                               1               --
      Callionymus                             3               --
      Batrachus                               1               --
    **Brachionichthys                         2               --
    **Saccarius                              --                1
      Clinus                                  1                1
    **Lepidoblennius                          1               --
      Cristiceps and Tripterygium             4                5
    **Patæcus                                 3               --
    **Acanthoclinus                          --                1
    **Diplocrepis                            --                1
    **Crepidogaster                           3                1
    **Trachelochismus                        --                1
    **Neophrynichthys                        --                1
      Centriscus                              2                1
      Notacanthus (sexspinis)                 1                1
    **Labrichthys                             8                2
    **Odax                                    5                1
    Coridodax                                --                1
    **Olistherops                             1               --
    **Siphonognathus                          1               --
      Gadus                                  --                1
      Merluccius                             --                1
      Lotella                                --                1
    **Pseudophycis                           --                1
      Motella                                --                1
      Bregmaceros                            --                1
     *Genypterus                              1                1
    **Lophonectes                             1               --
    **Brachypleura                           --                1
      Pseudorhombus                          --                1
    **Ammotretis                              1                1
    **Rhombosolea                             3                3
    **Peltorhamphus                          --                1
      Solea                                   1               --
      Aulopus                                 1               --
      Gonorhynchus (greyi)                    1                1
      Engraulis (encrasicholus)               1                1
      Clupea                                  1                1
    **Chilobranchus                           1               --
      Conger (vulgaris)                       1                1
      Ophichthys                              1                1
      Murænichthys                            1               --
      Congromuræna                           --                1
      Syngnathus                              5                2
      Ichthyocampus                          --                1
    **Nannocampus                             1               --
      Urocampus                               1               --
    **Stigmatophora                           2                1
      Solenognathus                           2                1
    **Phyllopteryx                            2               --
      Monacanthus                            15                1
      Ostracion                               3                1
     *Bdellostoma                            --                1
      Branchiostoma                           1                1

3. The coast-line of the _Chilian district_ extends over 20
degrees of latitude only, and is nearly straight. In its northern and
warmer parts it is of a very uniform character, and exposed to high and
irregular tides, and to remarkable and sudden changes of the levels of
land and water, which must seriously interfere with fishes living and
propagating near the shore. No river of considerable size interrupts
the monotony of the physical conditions, to offer an additional element
in favour of the development of littoral animals. In the southern
parts, where the coast is lined with archipelagoes, the climate is too
severe for the majority of fishes. All these conditions combine to
render this district comparatively poor as regards variety of Shore
fishes, as will be seen from the following list:--

*Callorhynchus; Scyllium, Acanthias, Spinax; Urolophus.

Serranus, Plectropoma, Polyprion, Pristipoma, Erythrichthys;
*Haplodactylus; *Scorpis; Chilodactylus, **Mendosoma; Sebastes,
*Agriopus; Trigla, Agonus; *Aphritis, *Eleginus, Pinguipes, Latilus,
Notothenia (1 sp.) Umbrina; Thyrsites; Trachurus, Caranx, *Seriolella;
Porichthys; **Myxodes, Clinus; Sicyases, Gobiesox.

Heliastes; **Malacopterus; *Labrichthys.

Merluccius; *Genypterus; Pseudorhombus.

Engraulis, Clupea; Ophichthys, Muræna.

Syngnathus.--*Bdellostoma.

Of these genera six only are not found in other districts of this
zone. Three are peculiar to the Chilian district; _Porichthys_
and _Agonus_ have penetrated so far southwards from the Peruvian
and Californian districts; and _Polyprion_ is one of those
extraordinary instances in which a very specialised form occurs at
almost opposite points of the globe, without having left a trace of
its previous existence in, or of its passage through, the intermediate
space.

4. The _Patagonian district_ is, with the exception of the
neighbourhood of the mouth of the Rio de la Plata, almost unknown.
In that estuary occur _Mustelus vulgaris_, two _Raja_, two _Trygon_,
several Sciænoids, _Paropsis signata_ and _Percophis brasilianus_
(two fishes peculiar to this coast), _Prionotus punctatus_, _Læmonema
longifilis_ (a Gadoid), a _Pseudorhombus_, two Soles, _Engraulis
olidus_, a _Syngnathus_, _Conger vulgaris_, and _Ophichthys ocellatus_;
and if we notice the occurrence of a _Serranus_ and _Caranx_, of
_Aphritis_ and _Pinguipes_, and of two or three _Clupea_, we shall have
enumerated all that is known of this fauna. The fishes of the southern
part, viz. the coast of Patagonia proper, southwards to Magelhæn’s
Straits, are unknown; which is the more to be regretted, as it is most
probably the part in which the characteristic types of this district
are most developed.


               V.--SHORE FISHES OF THE ANTARCTIC OCEAN.

To this fauna we refer the shore fishes of the southernmost extremity
of South America, from 50° lat. S., with Tierra del Fuego and the
Falkland Islands, and those of Kerguelen’s Land, with Prince Edward’s
Island. No fishes are known from the other oceanic islands of these
latitudes.

In the Southern Hemisphere surface fishes do not extend so far towards
the Pole as in the Northern; none are known from beyond 60° lat. S.,
and the Antarctic Fauna, which is analogous to the Arctic Fauna,
inhabits coasts more than ten degrees nearer to the equator. It is
very probable that the shores between 60° and the Antarctic circle
are inhabited by fishes sufficiently numerous to supply part of the
means of subsistence for the large Seals which pass there at least
some season of the year, but hitherto none have been obtained by
naturalists; all that the present state of our knowledge justifies us
in saying is, that the general character of the Fauna of Magelhæn’s
Straits and Kerguelen’s Land is extremely similar to that of Iceland
and Greenland.

As in the arctic Fauna, Chondropterygians are scarce, and represented
by _Acanthias vulgaris_ and species of _Raja_. _Holocephali_ have not
yet been found so far south, but _Callorhynchus_, which is not uncommon
near the northern boundary of this fauna, will prove to extend into it.

As to Acanthopterygians, _Cataphracti_ and _Scorpænidæ_ are
represented as in the arctic Fauna, two of the genera (_Sebastes_ and
_Agonus_) being identical. The _Cottidæ_ are replaced by six genera
of _Trachinidæ_, remarkably similar in form to arctic types; but
_Discoboli_ and the characteristic Arctic Blennioids are absent.

Gadoid Fishes reappear, but are less developed; as usual they are
accompanied by _Myxine_. The reappearance of so specialised a genus as
_Lycodes_ is most remarkable. Flat-fishes are scarce as in the North,
and belong to peculiar genera.

Physostomes are probably not entirely absent, but hitherto none have
been met with so far south. Lophobranchs are scarce, as in the Arctic
zone; however, it is noteworthy that a peculiar genus, with persistent
embryonic characters (_Protocampus_), is rather common on the shores of
the Falkland Islands.

The following are the genera known from this zone. Those with a
single asterisk (*) are known to extend into the Temperate zone, but
not beyond it; those with a double asterisk (**) are limited to the
Antarctic shores:--

                      Magelhæn’s and
                        Falkland.       Kerguelen.

      Acanthias vulgaris    1              --
      Raja                  1               2
      Psammobatis           1              --
      Sebastes              1              --
    **Zanclorhynchus       --               1
     *Agriopus              1              --
      Agonus                1              --
     *Aphritis              1              --
     *Eleginus              1              --
    **Chænichthys           1               1
     *Bovichthys            2              --
     *Notothenia            8               7
    **Harpagifer            1               1
      Lycodes               4              --
    **Magnea                1              --
      Lotella               1              --
      Merluccius            1              --
    **Lepidopsetta         --               1
    **Thysanopsetta         1              --
      Syngnathus            1              --
    **Protocampus           1              --
      Myxine                1              --
                          ---             ---
                           31              13
                          ===             ===

  [Illustration: Fig. 108.--_Chænichthys rhinoceratus_, shores
  of the Antarctic Ocean.]




                              CHAPTER XX.

                    DISTRIBUTION OF PELAGIC FISHES.


Pelagic Fishes,--that is, fishes inhabiting the surface of mid-ocean
(see p. 255), belong to various orders, viz. Chondropterygians,
Acanthopterygians, Physostomes, Lophobranchs, and Plectognaths. But
neither Anacanths nor Pharyngognaths contribute to this series of the
Marine Fauna. The following genera and families are included in it:--

CHONDROPTERYGII: Carcharias, Galeocerdo, Thalassorhinus, Zygæna,
Triænodon, Lamnidæ, Rhinodon, Notidanidæ, Læmargus, Euprotomicrus,
Echinorhinus, Isistius; Myliobatidæ.

ACANTHOPTERYGII: Dactylopterus, Micropteryx, Scombrina, Gastrochisma,
Nomeus, Centrolophus, Coryphænina, Seriola, Temnodon, Naucrates,
Psenes, Xiphiidæ, Antennarius.

PHYSOSTOMI: Sternoptychidæ, Scopelus, Astronesthes, Scombresocidæ
(majority).

LOPHOBRANCHII: Hippocampus.

PLECTOGNATHI: Orthagoriscus, and some other Gymnodonts.

Pelagic fishes differ much from one another in their mode of life.
The majority are excellent swimmers, which not only can move with
great rapidity, but also are possessed of great powers of endurance,
and are thus enabled to continue their course for weeks, apparently
without the necessity of rest: such are many Sharks, Scombroids,
Dolphins, Pilot-fish, Sword-fishes. In some, as in _Dactylopterus_
and _Exocoetus_, the ability of taking flying leaps out of the water
is superadded to the power of swimming (Flying-fishes). But in others
the power of swimming is greatly reduced, as in _Antennarius_,
_Hippocampus_, and Gymnodonts; they frequent places in the ocean
covered with floating seaweed, or drift on the surface without
resistance, at the mercy of wind and current. The _Echeneis_ or
Sucking-fishes attach themselves to other large fish, ships, or
floating objects, and allow themselves to be carried about, unless
change of climate or want of food obliges them to abandon their
temporary carrier. Finally, another class of Pelagic fishes come to
the surface of the ocean during the night only; in the day time they
descend to some depth, where they are undisturbed by the rays of the
sun or the agitation of the surface-water: such are _Brama_, the
_Sternoptychidæ_, _Scopelus_, _Astronesthes_; fishes, the majority of
which are provided with those extraordinary luminary organs that we
find so much developed in the true Deep-sea fishes. Indeed, this last
kind of Pelagic fishes forms a passage to the Deep-sea forms.

Pelagic fishes, like shore fishes, are most numerous in the
Tropical Zone; and, with few exceptions (_Echinorhinus_, _Psenes_,
_Sternoptychidæ_, _Astronesthes_), the same genera are represented
in the tropical Atlantic as well as in the Indo-Pacific. The number
of identical species occurring in both these oceans is great, and
probably still greater than would appear from systematic lists, in
which there are retained many specific names that were given at a time
when species were believed to have a very limited range. The Pelagic
fauna of the tropics gradually passes into that of the temperate
zones, only a few genera, like _Cybium_, _Psenes_, _Antennarius_,
being almost entirely confined to the tropics. All the other tropical
genera range into the temperate zones, but their representatives become
scarcer with the increasing distance from the equator. North of 40°
lat. N. many genera have disappeared, or are met with in isolated
examples only, as _Carcharias_, _Zygæna_, _Notidanus_, _Myliobatidæ_,
_Dactylopterus_, _Echeneis_, _Nomeus_, _Coryphæna_, _Schedophilus_,
_Seriola_, _Temnodon_, _Antennarius_, _Sternoptychidæ_, _Astronesthes_,
_Exocoetus_, _Tetrodon_, _Diodon_; and only one genus of Sharks,
_Galeocerdo_, approaches the Arctic circle. Some few species, like
_Antennarius_, _Scopelus_, are carried by currents near to the northern
confines of the temperate zones; but such occurrences are accidental,
and these fishes must be regarded as entirely foreign to the fauna of
those latitudes. On the other hand, some Pelagic fishes inhabit the
temperate zones, whilst their occurrence within the tropics is very
problematical; thus, in the Atlantic, _Thalassorhinus_, _Selache_,
_Læmargus_, _Centrolophus_, _Diana_, _Ausonia_, _Lampris_ (all genera
composed of one or two species only). Beside the Shark mentioned, no
other Pelagic fishes are known from the Arctic Ocean.

We possess very little information about the Pelagic fish-fauna of
the Southern oceans. So much only is certain, that the tropical forms
_gradually_ disappear; but it would be hazardous, in the present
state of our knowledge, to state even approximately, the limits of
the southward range of a single genus. Scarcely more is known about
the appearance of types peculiar to the Southern temperate zone; for
instance, the gigantic Shark (_Rhinodon_), representing the Northern
Selache, near the coasts of South Africa, and the Scombroid genus,
_Gastrochisma_, in the South Pacific.

The largest of marine fishes, _Rhinodon_, _Selache_, _Carcharodon_,
_Myliobatidæ_, _Thynnus_, _Xiphiidæ_, _Orthagoriscus_, belong to the
Pelagic Fauna. Young fishes are frequently found in mid-ocean, which
are the offspring of shore-fishes normally depositing their spawn near
the coast. The manner, in which this fry passes into the open sea, is
unknown; for it has not yet been ascertained whether it is carried by
currents from the place where it was deposited originally, or whether
shore-fishes sometimes spawn at a distance from the coast. We may
remember that shore-fishes inhabit not only coasts but also submerged
banks with some depth of water above, and that, by the action of the
water, spawn deposited on these latter localities is very liable to
be dispersed over wide areas of the ocean. Embryoes of at least some
shore-fishes hatched under abnormal conditions seem to have an abnormal
growth up to a certain period of their life, when they perish. The
_Leptocephali_ must be regarded as such abnormally developed fish
(see p. 179). Fishes of a similar condition are the so-called Pelagic
_Plagusiæ_, young Pleuronectoids, the origin of which is still unknown.
As mentioned before, Flat-fishes, like all the other Anacanths, are
otherwise not represented in the Pelagic fauna.

  [Illustration: Figs. 109 and 110.--_Antennarius
  candimaculatus_, a pelagic fish, from the Indian Ocean.]




                             CHAPTER XXI.

                      THE FISHES OF THE DEEP SEA.


The knowledge of the existence of deep-sea fishes is one of the
recent discoveries of ichthyology. It is only about twenty years ago
that, from the evidence afforded by the anatomical structure of a
few singular fishes obtained in the North Atlantic, an opinion was
expressed that these fishes inhabited great depths of the ocean, and
that their organisation was specially adapted for living under the
physical abyssal conditions. These fishes agreed in the character
of their connective tissue, which was so extremely weak as to yield
to, and to break under, the slightest pressure, so that the greatest
difficulty is experienced to preserve their body in its continuity.
Another singular circumstance was, that some of the specimens were
picked up floating on the surface of the water, having met their
deaths whilst engaged in swallowing or digesting another fish not much
inferior or even superior in size to themselves.

The first peculiarity was accounted for by the fact that, if those
fishes really inhabited the great depths supposed, their removal from
the enormous pressure under which they lived would be accompanied by
such an expansion of gases within their tissues as to rupture them, and
to cause a separation of the parts which had been held together by the
pressure. The second circumstance was explained thus:--A raptatorial
fish organised to live at a depth of between 500 and 800 fathoms seizes
another usually inhabiting a depth of between 300 and 500 fathoms. In
its struggles to escape, the fish seized, nearly as large or strong as
the attacking fish, carries the latter out of its depth into a higher
stratum, where the diminished pressure causes such an expansion of
gases as to make the destroyer with its victim rise with increasing
rapidity towards the surface, which they reach dead or in a dying
condition. Specimens in this condition are not rarely picked up; and
as, of course, comparatively few can by accident fall into the hands of
naturalists, occurrences of the kind related must happen very often.

Thus, the existence of fishes peculiarly adapted for the deep sea has
been a fact maintained and admitted for some time in Ichthyology; and
as the same genera and species were found at very distant parts of
the ocean, it was further stated that those Deep-sea fishes were not
limited in their range, and that, consequently, the physical conditions
of the depths of the ocean must be the same or nearly the same over
the whole globe. That Deep-sea fishes were not of a peculiar order,
but chiefly modified forms of surface types, was another conclusion
arrived at from the sporadic evidence collected during the period which
preceded systematic deep-sea dredging.

However, nothing was positively known as to the exact depths inhabited
by those fishes until observations were made during the voyage of
H.M.S. “Challenger.” The results obtained by this expedition afforded a
surer and more extended basis for our knowledge of Deep-sea fishes.

The physical conditions of the deep sea, which must affect the
organisation and distribution of fishes, are the following:--

1. Absence of sunlight. Probably the rays of the sun do not penetrate
to, and certainly do not extend beyond, a depth of 200 fathoms,
therefore we may consider this to be the depth where the Deep-sea
fauna commences. Absence of light is, of necessity, accompanied by
modifications of the organs of vision and by simplification of colours.

2. The absence of sunlight is in some measure compensated for by the
presence of phosphorescent light, produced by many marine animals, and
also by numerous Deep-sea fishes.

3. Depression and equality of the temperature. At a depth of 500
fathoms the temperature of the water is already as low as 40° Fahr.,
and perfectly independent of the temperature of the surface-water; and
from the greatest depths upwards to about 1000 fathoms the temperature
is uniformly but a few degrees above freezing-point. Temperature,
therefore, ceases to offer an obstacle to the unlimited dispersal of
Deep-sea fishes.

4. The increased pressure by the water. The pressure of the atmosphere
on the level of the sea amounts to fifteen pounds per square inch of
the surface of the body of an animal; but the pressure amounts to a ton
weight for every 1000 fathoms of depth.

5. With the sunlight, vegetable life ceases in the depths of the sea.
All Deep-sea fishes are therefore carnivorous; the most voracious
feeding frequently on their own offspring, and the toothless kinds
being nourished by the animalcules which live on the bottom, or which,
“like a constant rain,” settle down from the upper strata towards the
bottom of the sea.

6. The perfect quiet of the water at great depths. The agitation of
the water, caused by the disturbances of the air, does not extend
beyond the depth of a few fathoms; below this surface-stratum there is
no other movement except the quiet flow of ocean-currents, and near
the bottom of the deep sea the water is probably in a state of almost
entire quiescence.

The effect upon fishes of the physical conditions described is
clearly testified by the modification of one or more parts of their
organisation, so that every Deep-sea fish may be recognised as such,
without the accompanying positive evidence that it has been caught
at a great depth; and _vice versa_, fishes reputed to have been
obtained at a great depth, and not having any of the characteristics
of the dwellers of the deep sea, must be regarded as surface-fishes.

The most striking characteristic, found in many Deep-sea fishes,
is in relation to the tremendous pressure under which they live.
Their osseous and muscular systems are, as compared with the same
parts of surface-fishes, very feebly developed. The bones have a
fibrous, fissured, and cavernous texture; are light, with scarcely
any calcareous matter, so that the point of a needle will readily
penetrate them without breaking. The bones, especially the vertebræ,
appear to be most loosely connected with one another; and it requires
the most careful handling to prevent the breaking of the connective
ligaments. The muscles, especially the great lateral muscles of the
trunk and tail, are thin, the fascicles being readily separated from
one another or torn, the connective tissue being extremely loose,
feeble, or apparently absent. This peculiarity has been observed
in the _Trachypteridæ_, _Plagyodus_, _Chiasmodus_, _Melanocetus_,
_Saccopharynx_. But we cannot assume that it actually obtains whilst
those fishes exist under their natural conditions. Some of them are
most rapacious creatures which must be able to execute rapid and
powerful movements to catch and overpower their prey; and for that
object their muscular system, thin as its layers may be, must be as
firm, and the chain of the segments of their vertebral column as firmly
linked together as in surface-fishes. Therefore, it is evident that the
change which the body of those fishes has undergone on their withdrawal
from the pressure under which they live is a much aggravated form of
the affection that is experienced by persons reaching great altitudes
in their ascent of a mountain or in a balloon. In every living organism
with an intestinal tract there are accumulations of free gases; and,
moreover, the blood and other fluids, which permeate every part of the
body, contain gases in solution. Under greatly diminished pressure
these gases expand, so that, if the withdrawal from a depth is not
an extremely slow and gradual process, the various tissues must be
distended, loosened, ruptured; and what is a vigorous fish at a depth
of 500 or more fathoms, appears at the surface as a loosely-jointed
body which, if the skin is not of sufficient toughness, can only be
kept together with difficulty. At great depths a fibrous osseous
structure and a thin layer of muscles suffices to obtain the same
results for which, at the surface, thickness of muscle and firm osseous
or cartilaginous tissue are necessary.

The muciferous system of many Deep-sea fishes is developed in an
extraordinary degree. We find already in fishes which are comparatively
little removed from the surface (that is to depths of 100–200 fathoms),
the lateral line much wider than in their congeners or nearest allies
which live on the surface, as in _Trachichthys_, _Hoplostethus_, many
_Scorpænidæ_. But in fishes inhabiting depths of 1000 and more fathoms,
the whole muciferous system is dilated; it is especially the surface of
the skull which is occupied by large cavities (_Macruridæ_, deep-sea
_Ophidiidæ_), and the whole body seems to be covered with a layer of
mucus. These cavities collapse and shrink in specimens which have been
preserved in spirit for some time, but a re-immersion in water for a
short time generally suffices to show the immense quantity of mucus
secreted by them. The physiological use of this secretion is unknown;
it has been observed to have phosphorescent properties in perfectly
fresh specimens.

The colours of Deep-sea fishes are extremely simple, their bodies
being either black or silvery; in a few only are some filaments or the
fin-rays of a bright scarlet colour. Among the black forms albinoes are
not scarce.

The organ of sight is the first to be affected by a sojourn in deep
water. Even in fishes which habitually live at a depth of only 80
fathoms, we find the eye of a proportionally larger size than in
their representatives at the surface. In such fishes the eyes increase
in size with the depth inhabited by them, down to the depth of 200
fathoms, the large eyes being necessary to collect as many rays of
light as possible. Beyond that depth small-eyed fishes as well as
large-eyed occur, the former having their want of vision compensated
for by tentacular organs of touch, whilst the latter have no such
accessory organs, and evidently see only by the aid of phosphorescence.
In the greatest depths blind fishes occur with rudimentary eyes and
without special organs of touch.

Many fishes of the deep sea are provided with more or less numerous,
round, shining, mother-of-pearl-coloured bodies, imbedded in the
skin. These so-called phosphorescent or luminous organs are either
larger bodies of an oval or irregularly elliptical shape placed on the
head, in the vicinity of the eye, or smaller round globular bodies
arranged symmetrically in series along the side of the body and tail,
especially near the abdominal profile, less frequently along the back.
The former have not yet been anatomically examined. The number of
pairs of the latter is in direct relation to that of the segments of
the vertebral column, the muscular system, etc. (meta*-meres); and
two kinds may be distinguished differing from each other in their
anatomical structure. The organs of one kind consist of an anterior,
biconvex, lens-like body, which is transparent during life, simple
or composed of rods (_Chauliodus_); and of a posterior chamber which
is filled with a transparent fluid, and coated with a dark membrane
composed of hexagonal cells, or of rods arranged as in a retina. This
structure is found in _Astronesthes_, _Stomias_, _Chauliodus_, etc. In
the other kind the organ shows throughout a simply glandular structure,
but apparently without an efferent duct (_Gonostoma_, _Scopelus_,
_Maurolicus_, _Argyropelecus_). Branches of the spinal nerves run to
each organ, and are distributed over the retina-like membrane or the
glandular follicles. The former kind of organs are considered by some
naturalists true organs of vision (accessory eyes), the function of the
latter being left unexplained by them.

Although, thus, these organs morphologically differ from each other,
there is no doubt that the functions of all have some relation to the
peculiar conditions of light under which the fishes provided with them
live; these fishes being either deep-sea forms or nocturnal pelagic
kinds. There are three possible hypotheses as to the function of these
organs:--

1. All the different kinds of organs are sensory, or, in other words,
accessory eyes.

2. Only the organs with a lenticular body are sensory, and those with a
glandular structure produce and emit phosphorescent light.

3. All are producers of light.

There are very serious objections to adopting the first view.
_Scopelus_ and _Argyropelecus_ possess not only perfectly developed,
but even large eyes, specially adapted for a nocturnal life; and
therefore accessory organs of vision must appear to be quite
superfluous to them. On the other hand, in Deep-sea fishes without
external eyes, which would seem to especially require these metameric
organs of sense, they are invariably absent. And, finally, it is
quite inconceivable that the glandular structures should have the
faculty of conveying impressions of light to the nervous centre.
The second supposition seems therefore to be nearer the truth; and
is supported by the fact that the glandular organs of Scopeli have
actually been observed to gleam with phosphorescent light, and by the
obvious morphological similarity of the organs with a lenticular body
and retina-like membrane to an organ of vision. We are, moreover,
justified, from an _à priori_ consideration, in supposing that in
depths to which no sunlight descends, and which are illuminated by
phosphorescent light only, peculiar organs of vision would have been
developed. On the other hand, this supposition is opposed by the fact
that many fishes which dwell in those abyssal depths are provided
with large ordinary eyes (as the _Trachypteri_, the majority of
_Macruridæ_), and, therefore, that the ordinary organ of vision is
quite sufficient for seeing by phosphorescent light. Thus, whilst we
must admit that those compound organs may prove to be organs of sense,
we maintain at the same time that their morphological nature is not
opposed to the belief that they too, like the glandular organs, are
producers of light. It may be produced at the bottom of the posterior
chamber, and emitted through the lenticular body in particular
directions, with the same effect as light is sent through the convex
glass of a “bull’s eye.” This hypothesis seems to be less bold than the
other, which would require us to believe that vertebrate animals, with
a nervous centre specialised for the reception of the impressions of
the higher senses, should receive them through the spinal chord.

   [See _Ussow_, “Ueber den Bau der sogenannten
   augenaehnlichen Flecken einiger Knochenfische.” St. Petersburg,
   Bullet. 1879.]

Whenever we find in a fish long delicate filaments, developed in
connection with the fins or the extremity of the tail, we may
conclude that it is an inhabitant of still water and of quiet habits.
Many deep-sea fishes (_Trachypteridæ_, _Macruridæ_, _Ophidiidæ_,
_Bathypterois_) are provided with such filamentous prolongations, the
development of which is perfectly in accordance with their sojourn in
the absolutely quiet waters of abyssal depths.

Some of the raptatorial Deep-sea fishes have a stomach so distensible
and capacious that it can receive a fish of twice or thrice the bulk
of the destroyer (_Melanocetus_, _Chiasmodus_, _Saccopharynx_).
Deglutition is performed in them not by means of the muscles of the
pharynx, as in other fishes, but by the independent and alternate
action of the jaws, as in Snakes. These fishes cannot be said to
swallow their food, but rather draw themselves over their victim, in
the fashion of an _Actinia_.

Before the voyage of H.M.S. “Challenger,” scarcely thirty Deep-sea
fishes were known. This number is now much increased by the discovery
of many new species and genera; but, singularly, no new types of
families were discovered: nothing but what might have been expected
from our previous knowledge of this group of fishes. Modifications of
certain organs, perfectly novel, and of the greatest interest, were
found, as we shall see in the “Systematic Part;” but the most important
results of this voyage are that the general character of the abyssal
fish-fauna, the abundance of fishes, and the exact depths to which
fishes may descend, have been ascertained.

However, the statements of the depths at which the fishes collected by
the “Challenger” were taken cannot be received without some critical
examination of each individual species. No precaution was taken to
keep the mouth of the dredge closed during its descent or ascent, and
therefore it is quite within the limits of probability that sometimes
fishes were accidentally enclosed within the dredge, whilst it was
traversing the surface strata. And this has happened more than once;
for it is quite certain that common surface fishes like _Sternoptyx_
and _Astronestles_, never ranged to a depth of 2500 fathoms. On the
other hand, the majority of the fishes obtained offer sufficient
evidence from their own organisation that they live on the bottom, and
are unable to support themselves in the water at a certain distance
from the bottom or surface; and, consequently, that they actually were
obtained at the depth to which the dredge descended.

As far as the observations go at present, no distinct bathymetrical
regions, which would be characterised by peculiar forms, can be
defined. The depths from 200 to 600 fathoms are inhabited by
numerous forms, still strongly reminding us of surface types. To this
fauna belong the few Chondropterygians of the deep sea, a Sebastes
and Setarches, a Beryx and Polymixia, a Cottus, etc.; but they are
associated with many others which descend to the greatest depths.
And before anything like a division into bathymetrical zones can be
attempted, the observations of the “Challenger” expedition must be
confirmed and supplemented by other series of similar systematic
observations. One of the most startling conclusions at which we would
have to arrive from the “Challenger” observations is, that some of the
species of Deep-sea fishes would range from a depth of some 300 fathoms
down to one of 2000 fathoms; or, in other words, that a fish which
has once attained in its organisation to that modification by which
it is enabled to exist under the pressure of half a ton, can easily
accommodate itself to one of two tons or more,--a conclusion which is
not in accordance with anatomical facts, and which must be confirmed by
other observations before we can adopt it. But if the vertical range of
Deep-sea fishes is actually as it appears from the “Challenger” lists,
then there is no more distinct vertical than horizontal distribution of
Deep-sea fishes.

The greatest depth reached hitherto by a dredge in which fishes were
enclosed is 2900 fathoms. But the specimens thus obtained belong to a
species (_Gonostoma microdon_), which seems to be extremely abundant
in upper strata of the Atlantic and Pacific, and were therefore most
likely caught by the dredge in its ascent. The next greatest depth,
viz., 2750 fathoms, must be accepted as one at which fishes undoubtedly
do live; the fish obtained from this depth of the Atlantic, _Bathyophis
ferox_, showing by its whole habit that it is a form living on the
bottom of the ocean.

The fish-fauna of the deep sea is composed chiefly of forms or
modifications of forms which we find represented at the surface in the
cold and temperate zones, or which appear as nocturnal pelagic forms.
The Chondropterygians are few in number, not descending to a depth of
more than 600 fathoms. The Acanthopterygians, which form the majority
of the coast and surface faunas, are also scantily represented; genera
identical with surface types are confined to the same inconsiderable
depths as the Chondropterygians, whilst those Acanthopterygians which
are so much specialised for the life in the deep sea as to deserve
generic separation, range from 200 to 2400 fathoms. Three distinct
families of Acanthopterygians belong to the deep-sea fauna, viz.
_Trachypteridæ_, _Lophotidæ_, and _Notacanthidæ_; they respectively
consist of three, one, or two genera only.

_Gadidæ_, _Ophidiidæ_, and _Macruridæ_ are very numerous, ranging
through all depths; they constitute about one-fourth of the whole
deep-sea fauna.

Of _Physostomi_, the families of _Sternoptychidæ_, _Scopelidæ_,
_Stomiatidæ_, _Salmonidæ_, _Bathythrissidæ_, _Alepocephalidæ_,
_Halosauridæ_, and _Murænidæ_ are represented. Of these the
_Scopeloids_ are the most numerous, constituting nearly another fourth
of the fauna. _Salmonidæ_ are scarce, with three small genera only.
_Bathythrissidæ_ include one species only, which is probably confined
in its vertical as well as horizontal range; it occurs at a depth
of about 350 fathoms in the sea of Japan. The _Alepocephalidæ_ and
_Halosauridæ_, known before the “Challenger” expedition from isolated
examples only, prove to be true, widely-spread, deep-sea types. Eels
are well represented, and seem to descend to the greatest depths.

_Myxine_ has been obtained from a depth of 345 fathoms.

It will be useful to append a complete list of Deep-sea fishes, with
the depths as ascertained by the dredgings of the “Challenger:”--


                      _List of Deep-sea Fishes._

                                                  Fathoms.

    CHONDROPTERYGIANS--
      Raja                                            565
      Scyllium                                        400
      Centroscyllium                                  245
      Centrophorus                                345–500

    ACANTHOPTERYGIANS--
      Pomatomus                           (? down to) 200
      Sebastes                                        275
      Setarches                                       215
      Beryx                                           345
      Melamphaes                           (? beyond) 200
      Polymixia                                       345
      Nealotus
      Nesiarchus
      Aphanopus
      Euoxymetopon
      Lepidopus                                       345
      Gempylus
      Anomalops
    ? Antigonia
      Diretmus
      Cottus                                          565
      Bathydraco                                     1260
      Oneirodes
      Melanocetus johnsonii                          1850
           „      bispinosus                          360
      Himantolophus
      Chaunax                                         215
      Ceratias                                       2400
      Halieutichthys
      Dibranchus                                      360
      Trachypteridæ
      Lophotes
      Notacanthus rissoanus                          1875
           „      bonapartii                          400


    ANACANTHINI--

        Melanonus                                    1975
        Halargyreus
        Lotella marginata                         120–345
        Physiculus                                    345
        Uraleptus
        Læmonema
        Haloporphyrus australis                     55–70
              „       lepidion                    345–600
              „       rostratus                  600–1375
        Chiasmodus niger                             1500
        Sirembo grandis                              1875
           „    macrops                               375
           „    messieri                              345
           „    ocellatus                             350
           „    brachysoma                            350
        Acanthonus armatus                           1075
        Typhlonus nasus                              2440
        Aphyonus gelatinosus                         1400
        Rhinonus ater                                2150
        Bathynectes laticeps                         2500
             „      compressus                  1075–2500
             „      gracilis                         1400
        Pteridium
        Macrurus (12 species)                     120–700
        Coryphænoides norvegicus
             „        serratus
             „        nasutus                     345–565
             „        villosus                        345
             „        rudis                       500–650
             „        æqualis                         600
             „        crassiceps                  520–650
             „        microlepis                      215
             „        murrayi                        1100
             „        serrulatus                      700
             „        filicauda                 1800–2650
             „        variabilis                1375–2425
             „        affinis                        1900
             „        carinatus                       500
             „        longifilis                      565
             „        altipinnis                 565–1875
             „        asper                      500–1875
             „        leptolepis                 350–2050
             „        sclerorhynchus                 1090
             „        denticulatus                275–520
      Malacocephalus                                  350
      Bathygadus cottoides                        520–700
           „     multifilis                           500

    STERNOPTYCHIDÆ--
      Argyropelecus                                  1127 [?]
      Sternoptyx                                   0–2500 [?]
      Polyipnus                                       255
      Gonostoma denudatum
           „    microdon                         500–2900 [?]
           „    elongatum                         360–800
           „    gracile                          345–2425
      Chauliodus                                 565–2560

    SCOPELIDÆ--
      Bathysaurus ferox                              1100
           „      mollis                        1875–2385
      Bathypterois longifilis                     520–630
           „       longipes                          2650
           „       quadrifilis                    500–770
           „       longicauda                        2550
      Chlorophthalmus agassizii                       215
           „          nigripinnis                     120
           „          gracilis                  1100–1425
      Scopelus engraulis                              255
           „   antarcticus                           1950
           „   mizolepis                              800
           „   dumerilii                              215
           „   macrolepidotus                     520–630
           „   crassiceps                        675–1550
           „   macrostoma                       2350–2425
           „   microps                               1375
      Odontostomus hyalinus
      Odontostomus humeralis                          500
      Nannobrachium nigrum                            500
      Ipnops murrayi                            1600–2150
      Paralepis
      Sudis
      Plagyodus

    STOMIATIDÆ--
      Astronesthes niger                             2500 [?]
      Stomias boa                                450–1800
         „    barbatus
         „    ferox
      Echiostoma barbatum
          „      micripnus                           2150
          „      microdon                            2440
      Malacosteus niger
           „      indicus                             500
      Bathyophis ferox                               2750

    SALMONIDÆ--
      Argentina
      Microstoma
      Bathylagus antarcticus                         1950
          „      atlanticus                          2040

    BATHYTHRISSIDÆ--
      Bathythrissa dorsalis                           345

    ALEPOCEPHALIDÆ--
      Alepocephalus rostratus
           „        niger                            1400
      Platytroctes apus                              1500
      Bathytroctes microlepis                        1090
           „       rostratus                          675
           „       macrolepis                        2150
      Xenodermichthys                                 345

    HALOSAURIDÆ--
      Halosaurus owenii
           „     affinis                              565
           „     macrochir                      1090–1375
           „     mediorostris                         700
           „     rostratus                           2750


    MURÆNIDÆ--
      Nemichthys scolopacea
          „      infans                          500–2500
      Cyema atrum                               1500–1800
      Saccopharynx
      Synaphobranchus pinatus                    345–1200
            „         bathybius                 1875–2050
            „         brevidorsalis             1075–1375
            „         affinis                         345
      Nettastoma parviceps                            345

    CYCLOSTOMATA--
      Myxine australis                                345


  [Illustration: Fig. 111.--_Chiasmodus niger_; obtained in
  the North Atlantic at a depth of 1500 fathoms; the specimen has
  swallowed a large Scopelus (_s_); _o_, ventral fin.]




                   SYSTEMATIC AND DESCRIPTIVE PART.


The Class of Fishes is divided into four sub-classes:--

  I. PALÆICHTHYES.--Heart with a contractile conus arteriosus;
intestine with a spiral valve; optic nerves non-decussating, or only
partially decussating.

 II. TELEOSTEI.--Heart with a non-contractile bulbus arteriosus;
intestine without spiral valve; optic nerves decussating. Skeleton
ossified, with completely separated vertebræ.

III. CYCLOSTOMATA.--Heart without bulbus arteriosus; intestine
simple. Skeleton cartilaginous and notochordal. One nasal aperture
only. No jaws; mouth surrounded by a circular lip.

 IV. LEPTOCARDII.--Heart replaced by pulsating sinuses; intestine
simple. Skeleton membrano-cartilaginous and notochordal. No skull; no
brain.


                    FIRST SUB-CLASS: PALÆICHTHYES.

_Heart with a contractile conus arteriosus;[30] intestine with a
spiral valve;[31] optic nerves non-decussating, or only partially
decussating;[32] skeleton cartilaginous or osseous._

This sub-class comprises the Sharks and Rays, and the Ganoid fishes.
Although based upon a singular concurrence of most important
characters, its members exhibit as great a diversity of form, and as
manifold modifications in the remainder of their organisation as the
_Teleostei_. The _Palæichthyes_ stand to the _Teleostei_ in the same
relation as the Marsupials to the Placentalia. Geologically, as a
sub-class, they were the predecessors of Teleosteous fishes; and it is
a remarkable fact that all those modifications which show an approach
of the ichthyic type to the Batrachians are found in this sub-class. We
divide it into two orders: _Chondropterygii_ and _Ganoidei_.


                     FIRST ORDER: CHONDROPTERYGII.

_Skeleton cartilaginous. Body with medial and paired fins, the
hinder pair abdominal. Vertebral column generally heterocercal, the
upper lobe of the caudal fin produced. Gills attached to the skin by
the outer margin, with several intervening gill-openings: rarely one
external gill-opening only. No gill-cover. No air-bladder. Two, three,
or more series of valves in the conus arteriosus. Ova large and few
in number,[33] impregnated and, in some species, developed within a
uterine cavity. Embryo with deciduous external gills.[34] Males with
intromittent organs attached to the ventral fins.[35]_

This order, for which, also, the name _Elasmobranchii_ has
been proposed (by Bonaparte), comprises the Sharks and Rays and
Chimæras, and is divided into two suborders: _Plagiostomata_ and
_Holocephala_.


                    FIRST SUB-ORDER: PLAGIOSTOMATA.

_From five to seven gill-openings. Skull with a suspensorium and the
palatal apparatus detached. Teeth numerous._

The Plagiostomes differ greatly among each other with regard to the
general form of their body: in the Sharks or _Selachoidei_ the
body is elongate, more or less cylindrical, gradually passing into the
tail; their gill-openings are lateral. In the Rays, or _Batoidei_,
the gill-openings are always placed on the abdominal aspect of the
fish; the body is depressed, and the trunk, which is surrounded by the
immensely developed pectoral fins, forms a broad flat disk, of which
the tail appears as a thin and slender appendage. Spiracles are always
present; the number of gill-openings is constantly five; no anal fin;
dorsal fins, if present, situated on the tail. However, some of the
Rays approach the Sharks in having the caudal portion less abruptly
contracted behind the trunk.

Fossil Plagiostomes are very numerous in all formations. Some of
the earliest determinable fish remains are believed to be, or are,
derived from Plagiostomes. Those which can be referred to any of
the following families will be mentioned subsequently: but there
are others, especially fin-spines, which leave us in doubt to which
group of Plagiostomes their owners had any affinity, thus _Onchus_
from the upper Silurian, continuing to carboniferous formations;
_Dimeracanthus_, _Homocanthus_, from the Devonian; _Oracanthus_,
_Gyracanthus_, _Tristychius_, _Astroptychius_, _Ptychacanthus_,
_Sphenacanthus_, etc., from carboniferous formations; _Leptacanthus_,
from the coal to the Oolite; _Cladacanthus_, _Cricacanthus_,
_Gyropristis_, and _Lepracanthus_, from the coal measures;
_Nemacanthus_, _Liacanthus_, from the Trias; _Astracanthus_,
_Myriacanthus_, _Pristacanthus_, from the Jurassic group.


                        A. SELACHOIDEI: SHARKS.

The elongate cylindrical body, generally terminating in a more or
less pointed snout, and passing into a powerful and flexible tail,
blade-like at its extremity, gives to the Sharks a most extraordinary
power of swimming, with regard to endurance as well as rapidity of
motion. Many, especially the larger kinds, inhabit the open ocean,
following ships for weeks, or pursuing shoals of fishes in their
periodical migrations. Other large-sized sharks frequent such parts
of the coast as offer them abundance of food; whilst the majority of
the smaller kinds are shore fishes, rarely leaving the bottom, and
sometimes congregating in immense numbers. The movements of sharks
resemble in some measure those of snakes, their flexible body being
bent in more than one curve when moving.

Sharks are most numerous in the seas between the Tropics, and become
scarcer beyond, a few only reaching the Arctic circle; it is not known
how far they advance southwards towards the Antarctic region. Some
species enter fresh waters, and ascend large rivers, like the Tigris
or Ganges, to a considerable distance. The pelagic as well as the
shore species have a wide geographical range. Very few descend to a
considerable depth, probably not exceeding 500 fathoms. There are about
140 different species known.

Sharks have no scales like those of other fishes; their integuments
are covered with calcified papillæ which, under the microscope, show a
structure similar to that of teeth. If the papillæ are small, pointed,
and close set, the skin is called “shagreen;” rarely they are larger,
appearing as bucklers or spines, of various sizes.

These fishes are exclusively carnivorous, and those armed with powerful
cutting teeth are the most formidable tyrants of the ocean. They have
been known to divide the body of a man in two at one bite, as if by
the sweep of a sword. Some of the largest sharks, however, which
are provided with very small teeth, are almost harmless, feeding on
small fishes only or marine invertebrates. Others, particularly of
the smaller kinds, commonly called “Dog-fishes,” have short or obtuse
teeth, and feed on shells or any other animal substance. Sharks scent
their food from a distance, being readily attracted by the smell of
blood or decomposing bodies.

In China and Japan, and many other eastern countries, the smaller kinds
of sharks are eaten. Sharks’ fins form in India and China a very
important article of trade, the Chinese preparing from them gelatine,
and using the better sorts for culinary purposes. The fins are obtained
not exclusively from Sharks but also from Rays, and assorted in two
kinds, viz. “white and black.” The white consist exclusively of the
dorsal fins, which are on both sides of the same uniform light colour,
and reputed to yield more gelatine than the other fins. The pectoral,
ventral, and anal fins pass under the denomination of black fins; the
caudal fin is not used. One of the principal places where shark fishery
is practised as a profession is Kurrachee. Dr. Buist, writing in 1850
(“Proc. Zool. Soc.” 1850, p. 100), states that there are thirteen
large boats, with crews of twelve men each, constantly employed in
this pursuit; that the value of the fins sent to the market varies
from 15,000 to 18,000 rupees; that one boat will sometimes capture at
a draught as many as one hundred sharks of various sizes; and that the
number total of sharks captured during the year amounts probably to not
less than 40,000. Large quantities are imported from the African coast
and the Arabian Gulf, and various ports on the coast of India. In the
year 1845–46, 8770 cwt. of sharks’ fins were exported from Bombay to
China.


                      FIRST FAMILY--CARCHARIIDÆ.

_Eye with a nictitating membrane. Mouth crescent-shaped, inferior.
Anal fin present. Two dorsal fins, the first opposite to the space
between pectoral and ventral fins, without spine in front._

   CARCHARIAS.--Snout produced in the longitudinal axis of the
   body; mouth armed with a series of large flat triangular teeth,
   which have a smooth cutting or serrated edge. Spiracles absent.
   A transverse pit on the back of the tail, at the root of the
   caudal fin.

This genus comprises the true Sharks, common in the tropical, but less
so in the temperate seas. Between thirty and forty different species
have been distinguished, of which one of the most common is the “Blue
Shark” (_Carcharias glaucus_). Individuals of from twelve to fifteen
feet are of very common occurrence, but some of the species attain a
much larger size, and a length of 25 and more feet. Fishes of this
genus or of closely allied genera (_Corax_, _Hemipristis_) are not
uncommon in the chalk and tertiary formations.

   GALEOCERDO.--Teeth large, flat, triangular, oblique, serrated
   on both edges, with a deep notch on the outer margin. Spiracles
   small. A pit on the tail, above and below, at the root of the
   caudal fin. Two notches on the under caudal border, one of them
   at the end of the spine.

  [Illustration: Fig. 112.--Dentition of the Blue Shark (Carcharias
  glaucus); the single teeth are of the natural size.]

Three species, of which one (_G. arcticus_) is confined to the
arctic and sub-arctic oceans. The others inhabit temperate and tropical
seas, and all attain to a very large size.

   GALEUS.--Snout produced in the longitudinal axis of the
   body; teeth equal in both jaws, rather small, flat, triangular,
   oblique, serrated and with a notch. Spiracles small. No pit at
   the commencement of the caudal fin, which has a single notch on
   its lower margin.

These are small sharks, commonly called “Tope.” The species found on
the British coast is spread over nearly all the temperate and tropical
seas, and is common in California and Tasmania. It lives on the bottom,
and is very troublesome to fishermen by constantly taking away bait or
driving away the fishes which they desire to catch.

   ZYGÆNA.--The anterior part of the head is broad, flattened, and
   produced into a lobe on each side, the extremity of which is
   occupied by the eye. Caudal fin with a single notch at its lower
   margin. A pit at the root of the caudal fin. Spiracles none.
   Nostrils situated on the front edge of the head.

The “Hammerheads,” or Hammerheaded Sharks, have a dentition very
similar to that of _Carcharias_, and although they do not attain to
the same large size, they belong to the most formidable fishes of
the ocean. The peculiar form of their head is quite unique among
fishes; young examples have the lateral extension of the skull much
less developed than adults. Five species are known, which are most
abundant in the tropics. By far the most common is _Zygæna malleus_,
which occurs in nearly all tropical and sub-tropical seas. Specimens
of this species may be often seen ascending from the clear blue depths
of the ocean like a great cloud. Cantor found in a female, nearly 11
feet long, thirty-seven embryons.--Hammerheads have lived from the
cretaceous epoch.

   MUSTELUS.--The second dorsal fin is not much smaller than the
   first. No pit at the root of the caudal, which is without
   distinct lower lobe. Snout produced in the longitudinal axis
   of the body. Spiracles small, behind the eyes. Teeth small,
   numerous, similar in both jaws, obtuse, or with very indistinct
   cusps, arranged like pavement.

The “Hounds” are small Sharks, abundant on the coasts of all the
temperate and tropical seas; two of the five species known occur on the
coasts of Europe, viz. _M. lævis_ and _M. vulgaris_. Closely allied as
these two species are, they yet show a most singular difference, viz.
that a placenta is developed in the uterus for the attachment of the
embryo in _M. lævis_ (the Γαλεὁς λεȋος of Aristotle, to whom this fact
was already known); whilst the embryons of _M. vulgaris_ are developed
without such placenta (see _J. Müller_, “Abhandl. Ak. Wiss.” Berl.
1840). The Hounds are bottom fish, which feed principally on shells,
crustaceans, and decomposing animal substances.

       *       *       *       *       *

Several other genera belong to the family Carchariidæ, but it will
be sufficient to mention their names:--_Hemigaleus_, _Loxodon_,
_Thalassorhinus_, _Triænodon_, _Leptocarcharias_, and _Triacis_.


                        SECOND FAMILY--LAMNIDÆ.

_Eye without nictitating membrane. Anal fin present. Two dorsal fins;
the first opposite to the space between pectoral and ventral fins,
without spine in front. Nostrils not confluent with the mouth which is
inferior. Spiracles absent or minute._

All the fishes of this family attain to a very large size, and
are pelagic. But little is known of their reproduction. The first
appearance of this family is indicated by _Carcharopsis_, a genus from
carboniferous formations, the teeth of which differ from those of
_Carcharodon_ only by having a broad fold at the base. In the chalk and
tertiary formations almost all the existing genera are represented;
and, besides, _Oxytes_, _Sphenodus_, _Gomphodus_, and _Ancistrodon_,
which are known from teeth only, have been considered generically
distinct from the living Porbeagles.

   LAMNA (OXYRHINA).--The second dorsal and anal are very small.
   A pit at the root of the caudal, which has the lower lobe much
   developed. Side of the tail with a prominent longitudinal keel.
   Mouth wide. Teeth large, lanceolate, not serrated, sometimes
   with additional basal cusps. On each side of the upper jaw, at
   some distance from the symphysis, there is one or two teeth
   conspicuously smaller than the others. Gill-openings very wide.
   Spiracles minute.

  [Illustration: Fig. 113.--Upper and lower tooth of Lamna.]

Of the “Porbeagles,” three species have been described, of which
the one occurring in the North Atlantic, and frequently straying to
the British coasts (_L. cornubica_), is best known. It attains to a
length of ten feet, and feeds chiefly on fishes; its lanceolate teeth
are not adapted for cutting, but rather for seizing and holding its
prey, which it appears to swallow whole. According to Pennant it is
viviparous; only two embryoes were found in the female which came under
his observation. Haast has found this species also off the coast of New
Zealand.

   CARCHARODON.--The second dorsal and anal are very small. Pit at
   the root of the caudal, which has the lower lobe well developed.
   Side of the tail with a prominent longitudinal keel. Mouth wide.
   Teeth large, flat, erect, regularly triangular, serrated. On
   each side of the upper jaw, at some distance from the symphysis,
   there is one or two teeth conspicuously smaller than the others.
   Gill-openings wide.

One species only is known (_C. rondeletii_), which is the most
formidable of all Sharks. It is strictly pelagic; and appears to occur
in all tropical and sub-tropical seas. It is known to attain to a
length of 40 feet. The tooth figured here, of the natural size, is
taken from a jaw 20 inches wide in its transverse diameter (inside
measure), each half of the mandible measuring 22 inches.[36] The whole
length of the fish was 36½ feet.

Carcharodon teeth are of very common occurrence in various tertiary
strata, and have been referred to several species, affording ample
evidence that this type was much more numerously represented in that
geological epoch than in the recent fauna. Some individuals attained to
an immense size, as we may judge from teeth found in the Crag, which
are 4 inches wide at the base, and 5 inches long, measured along their
lateral margin. The naturalists of the “Challenger” expedition have
made the highly interesting discovery that teeth of similar size are
of common occurrence in the ooze of the Pacific, between Polynesia and
the west coast of America. As we have no record of living individuals
of that bulk having been observed, the gigantic species to which these
teeth belonged must have become extinct within a comparatively recent
period. Nothing is known of the anatomy, habits, and reproduction of
the surviving species, and no opportunity should be lost of obtaining
information on this Shark.

  [Illustration: Fig. 114.--Tooth of Carcharodon rondeletii.]

   ODONTASPIS.--The second dorsal and anal are not much smaller
   than the first dorsal. No pit at the root of the caudal. Side of
   the tail without keel. Mouth wide. Teeth large, awl-shaped, with
   one or two small cusps at the base. Gill-openings of moderate
   width.

Large Sharks from tropical and temperate seas; two species.

   ALOPECIAS.--The second dorsal and anal very small. Caudal fin
   of extraordinary length, with a pit at its root. No keel on the
   side of the tail. Mouth and gill-openings of moderate width.
   Teeth equal in both jaws, of moderate size, flat, triangular,
   not serrated.

This genus consists of one species only, which is known by the name of
“Fox-shark” or “Thresher.” It is the most common of the larger kinds
of Sharks which occur on the British coasts; and seems to be equally
common in other parts of the Atlantic and Mediterranean, as well as on
the coasts of California and New Zealand. It attains to a length of
fifteen feet, of which the tail takes more than one half; and is quite
harmless to man. It follows the shoals of Herrings, Pilchards, and
Sprats in their migrations, destroying incredible numbers. When feeding
it uses the long tail in splashing the surface of the water, whilst it
swims in gradually decreasing circles round a shoal of fishes, which
are thus kept crowded together, falling an easy prey to their enemy.
Statements that it has been seen to attack Whales and other large
Cetaceans, rest upon erroneous observations.

   SELACHE.--The second dorsal and anal very small. A pit at the
   root of the caudal fin, which is provided with a lower lobe.
   Side of the tail with a keel. Gill-openings extremely wide.
   Teeth very small, numerous, conical, without serrature or
   lateral cusps.

Also this genus consists of one species only, the “Basking Shark”
(Pélerin of the French). It is the largest Shark of the North Atlantic,
growing to a length of more than thirty feet. It is quite harmless if
not attacked; its food consisting of small fishes, and other small
marine animals swimming in shoals. On the west coast of Ireland it
is chased for the sake of the oil which is extracted from the liver,
one fish yielding from a ton to a ton and a-half. Its capture is not
unattended with danger, as one blow from the enormously strong tail is
sufficient to stave in the sides of a large boat. At certain seasons
it is gregarious, and many specimens may be seen in calm weather lying
together motionless, with the upper part of the back raised above the
surface of the water; a habit from which this Shark has derived its
name. The buccal and branchial cavities are of extraordinary width,
and, in consequence of the flabby condition of those parts, the head
presents a variable and singular appearance in specimens lying dead on
the ground. This peculiarity, as well as the circumstance that young
specimens have a much longer and more pointed snout than adult ones,
has led to the erroneous opinion that several different genera and
species of Basking Shark occur in the European seas. The branchial
arches of _Selache_ are provided with a very broad fringe of
long (five to six inches) and thin gill-rakers, possessing the same
microscopical structure as the teeth and dermal productions of Sharks.
Similar gill-rakers have been found in a fossil state in the Crag of
Anvers in Belgium, proving the existence of this Selachian type in the
tertiary epoch. Nothing is known of the reproduction of this fish.
The latest contributions to its history are by _Steenstrup_ in
“Overs. Dansk. Vidensk. Selsk., Forhandl.” 1873, and by _Pavesi_
in “Annal. Mus. Civ. Geneva,” 1874 and 1878.


                      THIRD FAMILY--RHINODONTIDÆ.

_No nictitating membrane. Anal fin present. Two dorsal fins, the
first nearly opposite to the ventrals, without spine in front. Mouth
and nostril near the extremity of the snout._

This small family comprises one species only, _Rhinodon typicus_,
a gigantic Shark, which is known to exceed a length of fifty feet,
but is stated to attain that of seventy. It does not appear to be
rare in the western parts of the Indian Ocean, and possibly occurs
also in the Pacific. It is one of the most interesting forms, not
unlike the Basking Shark of the Northern Seas, having gill-rakers like
that species; but very little is known of its structure and mode of
life. It is perfectly harmless, its teeth being extremely small and
numerous, placed in broad bands; it has been stated to feed on tang,
an observation which requires confirmation. The snout is very broad,
short, and flat; the eyes are very small. A pit at the root of the
caudal fin which has the lower lobe well developed; side of the tail
with a keel. A characteristic figure of this fish has been given by A.
Smith in his “Illustrations of the Zoology of South Africa,” Plate 26,
from a specimen which came ashore at the Cape of Good Hope.

  [Illustration: Fig. 115.--Dentition of Notidanus indicus. _a_,
  teeth in function; _b_, teeth in reserve; _u_, upper, and _l_,
  lower, tooth, of natural size.]


                      FOURTH FAMILY--NOTIDANIDÆ.

_No nictitating membrane. One dorsal fin only, without spine,
opposite to the anal._

   NOTIDANUS.--Dentition unequal in the jaws: in the upper jaw
   one or two pairs of awl-shaped teeth, the following six being
   broader, and provided with several cusps, one of which is much
   the strongest. Lower jaw with six large comb-like teeth on each
   side, beside the smaller posterior teeth. Spiracles small, on
   the side of the neck. No pit at the root of the caudal fin.
   Gill-openings wide, six in number in _Hexanchus_, seven in
   _Heptanchus_.

Four species are known, distributed over nearly all the tropical and
sub-tropical seas; they attain to a length of about fifteen feet.
Fossil teeth belonging to this type have been found in Jurassic and
later formations (_Notidanus_ and _Aellopos_).


                       FIFTH FAMILY--SCYLLIIDÆ.

_Two dorsal fins, without spine: the first above or behind the
ventrals; anal fin present. No nictitating membrane. Spiracle always
distinct. Mouth inferior. Teeth small, several series generally being
in function._

   SCYLLIUM.--The origin of the anal fin is always in advance of
   that of the second dorsal. Nasal cavity separate from the mouth.
   Teeth small, with a middle longer cusp, and generally one or two
   small lateral cusps arranged in numerous series. Eggs similar to
   those of the Rays (Fig. 79, p. 167).

The fishes of this genus are of small size, and commonly called
“Dog-fishes.” They are coast fishes, living on the bottom, and feeding
on Crustaceans, dead fishes, etc. None of the eight species known have
a very wide distribution, but where they occur they are generally
sufficiently abundant to prove troublesome to fishermen. They inhabit
most parts of the temperate and tropical seas. On the British coasts
two species are found, the “Larger” and “Lesser spotted Dog-fish,”
_Scyllium canicula_ and _Scyllium catulus_, which are said to be more
plentiful among the Orkney Islands than elsewhere. They are scarcely
ever brought to market; but the fishermen of some localities do not
disdain to eat them. Their flesh is remarkably white, a little
fibrous, and dry. In the Orkneys they are skinned, split up, cleaned,
and then spread out on the rocks to dry for home consumption. The skins
are used for smoothing down cabinet-work. It would be worth while to
apply the fins of these and other Sharks, which are so extensively
used in China for making gelatine soups, to the same purpose in this
country, or to dry them for exportation to the East. Most of the
species of Dog-fishes are spotted, and those of the allied genera,
_Parascyllium_ and _Chiloscyllium_, very handsomely ornamented.

Closely allied to _Scyllium_ is _Pristiurus_, from the coasts of
Europe, which is provided with a series of small flat spines on each
side of the upper edge of the caudal fin.

Fossil forms of Dog-fishes are not scarce in the Lias and Chalk:
_Scylliodus_, _Palæoscyllium_, _Thyellina_, _Pristiurus_.

   GINGLYMOSTOMA.--The second dorsal fin opposite to, and somewhat
   in advance of, the anal. Eyes very small; spiracle minute and
   behind the eye. Nasal and buccal cavities confluent. The nasal
   valves of both sides form one quadrangular flap in front of the
   mouth, each being provided with a free cylindrical cirrhus. The
   fourth and fifth gill-openings are close together. The teeth
   stand either in many series, each having a strong median cusp
   and one or two smaller ones on each side (_Ginglymostoma_), or
   they stand in a few (three) series only, the foremost only being
   in function, and each tooth having a convex, finely and equally
   serrated margin (_Nebrius_).

Four species from the tropical parts of the Atlantic and Indian Oceans,
attaining to a length of some 12 feet. Pelagic.

   STEGOSTOMA.--The first dorsal above the ventrals, the second in
   advance of the anal, which is very close to the caudal. Tail,
   with the caudal fin, exceedingly long, measuring one-half of the
   total length. Eyes very small, spiracle as wide as, and situated
   behind, the orbit. Nasal and buccal cavities confluent. Snout
   very obtuse; upper lip very thick, like a pad, bent downwards
   over the mouth, with a free cylindrical cirrhus on each side.
   Teeth small, trilobed, in many series, occupying in both jaws
   a transverse flat subquadrangular patch. The fourth and fifth
   gill-openings are close together.

The single species (_St. tigrinum_) for which this genus has been
formed, is one of the commonest and handsomest sharks of the Indian
Ocean. Young individuals keep generally close to the coasts, whilst
the adult, which are from 10 to 15 feet long, are not rarely met in
the open ocean. The colour is a brownish yellow, ornamented with black
or brown transverse bands, or with snuff-coloured rounded spots; hence
this shark is frequently mentioned by the names of “Zebra-Shark” or
“Tiger-Shark.”

  [Illustration: Fig. 116.--Chiloscyllium trispeculare, from
  North-western Australia.]

   CHILOSCYLLIUM.--The first dorsal fin above or behind the
   ventrals. Anal fin placed far behind the second dorsal, and very
   close to the caudal. Spiracle very distinct, below the eye.
   Nasal and buccal cavities confluent. Nasal valve folded, with a
   cirrhus. Teeth small, triangular, with or without lateral cusps.
   The two last gill-openings close together.

“Dog-fishes,” from the Indian Ocean, of small size. Four species are
known, of which one, _Ch. indicum_, is one of the commonest
shore-fishes on the coasts of this region, extending from the southern
extremity of the African Continent to Japan.

  [Illustration: Fig. 117.--Confluent nasal and buccal cavities of
  the same fish.]

   CROSSORHINUS.--The first dorsal behind the ventrals, the second
   in advance of the anal, which is very close to the caudal. Tail
   rather short. Eyes small. Spiracle a wide oblique slit, behind
   and below the eye. Nasal and buccal cavities confluent. Head
   broad, flat, with the snout very obtuse; mouth wide, nearly
   anterior. A free nasal cirrhus; sides of the head with skinny
   appendages. Anterior teeth rather large, long and slender,
   without lateral lobes, the lateral tricuspid, smaller, forming
   a few series only. The fourth and fifth gill-openings close
   together.

Three species are known from the Australian and Japanese coasts. They
are evidently ground-sharks, which lie concealed on the bottom watching
for their prey. In accordance with this habit their colour closely
assimilates that of a rock or stone covered with short vegetable and
coralline growth--a resemblance increased by the frond-like tentacles
on the side of the head. This peculiarity of the integuments, which is
developed in a yet higher degree in Pediculati and Lophobranchs, is not
met with in any other Selachian. These Sharks grow to a length of 10
feet.


                      SIXTH FAMILY--HYBODONTIDÆ.

_Two dorsal fins, each with a serrated spine. Teeth rounded,
longitudinally striated, with one larger, and from two to four smaller
lateral cusps. Skin covered with shagreen._

Extinct. From carboniferous, liassic, and triassic formations. Several
genera have been distinguished; and if _Cladodus_ belongs to this
family, it would have been represented even in the Devonian.

  [Illustration: Fig. 118.--Spine of Hybodus subcarinatus.]


                    SEVENTH FAMILY--CESTRACIONTIDÆ.

_No nictitating membrane. Two dorsal fins, the first opposite to
the space between pectoral and ventral fins; anal fin present. Nasal
and buccal cavities confluent. Teeth obtuse, several series being in
function._

  [Illustration: Fig. 119.--Jaws of Port Jackson Shark, Cestracion
  philippi.]

  [Illustration: Fig. 120.--Upper jaw of the same, half natural
  size.]

This family is one of particular interest, because representatives of
it occur in numerous modifications in primary and secondary strata.
Their dentition is uniformly adapted for the prehension and mastication
of crustaceous and hard-shelled animals. The fossil forms far exceeded
in size the species of the only surviving genus; they make, their
appearance with _Ctenoptychius_ in the Devonian; this is succeeded
in the coal-measures by _Psammodus_, _Chomatodus_, _Petrodus_,
_Coch__liodus_, _Polyrhizodus_, etc.; in the Trias and Chalk by
_Strophodus_, _Acrodus_, _Thectodus_, and _Ptychodus_. Of the 25 genera
known, 22 have lived in the periods preceding the Oolitic.

   CESTRACION (HETERODONTUS).--Each dorsal fin armed with a spine
   in front; the second in advance of the anal. Mouth rather
   narrow. Spiracles small, below the posterior part of the eye.
   Gill-openings rather narrow. Dentition similar in both jaws,
   viz. small obtuse teeth in front, which in young individuals are
   pointed and provided with from three to five cusps. The lateral
   teeth are large, padlike, twice as broad as long, arranged in
   oblique series, one series being formed by much larger teeth
   than those in the other series.

  [Illustration: Fig. 121.--Cochliodus contortus.]

  [Illustration: Fig. 122.--Cestracion galeatus, Australia.]

Four species are known from Japan, Amboyna, Australia, the Galapagoes
Islands, and California; none exceed a length of 5 feet. The egg has
been figured on p. 168 (Fig. 80).


                       EIGHTH FAMILY--SPINACIDÆ.

_No membrana nictitans. Two dorsal fins; no anal. Mouth but slightly
arched; a long, deep, straight, oblique groove on each side of the
mouth. Spiracles present; gill-openings narrow. Pectoral fins not
notched at their origin._

The oldest representative of this family (_Palæospinax_) occurs at
Lyme Regis; its skin is granular; each dorsal fin possesses a spine;
the teeth in the jaws are dissimilar--the upper being multicuspid,
longitudinally ribbed as in Hybodus, the lower smooth and tricuspid.
_Drepanophorus_ and _Spinax primævus_ occur in Cretaceous formations of
England and the Lebanon.

   CENTRINA.--Each dorsal fin with a strong spine. Trunk rather
   elevated, trihedral, with a fold of the skin running along each
   side of the belly. Teeth of the lower jaw erect, triangular,
   finely serrated; those of the upper slender, conical, forming a
   group in front of the jaw. Spiracles wide, behind the eye.

One species, _Centrina salviani_, from the Mediterranean and
neighbouring parts of the Atlantic; of small size.

   ACANTHIAS.--Each dorsal fin with a spine. Teeth equal in both
   jaws, rather small; their point is so much turned aside that
   the inner margin of the tooth forms the cutting edge. Spiracles
   rather wide, immediately behind the eye.

The two species of “Spiny Dog-fishes,” _A. vulgaris_ and _A.
blainvillii_, have a very remarkable distribution, being found in the
temperate seas of the Northern and Southern Hemispheres, but not in the
intermediate tropical zone. They are of small size, but occur at times
in incredible numbers, 20,000 having been taken in one scene on the
Cornish coast. They do much injury to the fishermen by cutting their
lines and carrying off their hooks.

   CENTROPHORUS.--Each dorsal fin with a spine which, however, is
   sometimes so small as to be hidden below the skin. Mouth wide.
   Teeth of the lower jaw with the point more or less inclined
   backwards and outwards. Upper teeth erect, triangular, or
   narrow, lanceolate, with a single cusp. Spiracles wide, behind
   the eye.

Eight species are known from the southern parts of the European seas,
and one from the Moluccas; they do not appear to exceed a length
of five feet. According to the observations of E. P. Wright, some
of the species at least live at a considerable depth, perhaps at a
greater depth than any of the other known Sharks. The Portuguese
fishermen fish for them in 400 or 500 fathoms with a line of some 600
fathoms in length. The Sharks caught were specimens of _Centrophorus
coelolepis_, from three to four feet long. “These sharks, as they
were hauled into the boat, fell down into it like so many dead pigs;
there was not the smallest motion of their bodies. There can be no
reasonable doubt that they were inhabitants of the same great depth as
_Hyalonema_” and that, in fact, they were killed by being dragged
to the surface from the pressure of water under which they lived.
The dermal productions of some of the species have a very peculiar
form, being leaf-shaped, pedunculate, or ribbed, or provided with an
impression.

   SPINAX.--Each dorsal fin with a spine. Teeth of the lower jaw
   with the point so much turned aside that the inner margin of
   the tooth forms the cutting edge. Upper teeth erect, each with
   a long-pointed cusp and one or two small ones on each side.
   Spiracles wide, superior, behind the eye.

Three small species from the Atlantic and the southern extremity of
America. _Centroscyllium_ is an allied genus from the coast of
Greenland.

   SCYMNUS.--Two short dorsal fins without spine, the first at a
   considerable distance from the ventrals. Dermal productions
   uniformly small. Nostrils at the extremity of the snout. Upper
   teeth small, pointed; lower much larger, dilated, erect,
   triangular, not very numerous. Spiracles wide.

A single species, _S. lichia_, is rather common in the Mediterranean
and the neighbouring parts of the Atlantic.

   LÆMARGUS.--All the fins small; two dorsal fins, without spine,
   the first at a considerable distance from the ventrals. Skin
   uniformly covered with minute tubercles. Nostrils near the
   extremity of the snout. The upper teeth small, narrow, conical;
   the lower teeth numerous, in several series, the point so much
   turned aside that the inner margin forms a cutting, non-serrated
   edge. Jaws feeble. Spiracles of moderate width.

  [Illustration: Fig. 123.--Dentition of the Greenland Shark. Some
  teeth are represented of the natural size; those of the lower jaw
  in three series.]

The “Greenland Shark” is an inhabitant of the Arctic regions, but
rarely straying to the latitudes of great Britain; it grows to a length
of about 15 feet, and, although it never or but rarely attacks man, is
one of the greatest enemies of the whale, which is often found with
large pieces bitten out of the tail by this Shark. Its voracity is so
great that, according to Scoresby, it is absolutely fearless of the
presence of man whilst engaged in feeding on the carcass of a whale,
so that it can be pierced through with a spear or knife without being
driven away. It is stated to be viviparous, and to produce about four
young at a birth.

  [Illustration: Fig. 124.--Læmargus borealis, Greenland Shark.]

   ECHINORHINUS.--Two very small dorsal fins, without spine, the
   first opposite to the ventrals. Skin with scattered large round
   tubercles. Nostrils midway between the mouth and the end of the
   snout. Teeth equal in both jaws, very oblique, the point being
   turned outwards; several strong denticulations on each side of
   the principal point. Spiracles small.

The “Spinous Shark” is readily recognised by the short bulky form of
its body, short tail, and large spinous tubercles. It is evidently a
ground-shark, which probably lives at some depth and but accidentally
comes to the surface. More frequently met with in the Mediterranean, it
has been found several times on the south coast of England, and near
the Cape of Good Hope.

_Euprotomicrus_ and _Isistius_ are two other genera of this family;
they are pelagic and but little known.


                        NINTH FAMILY--RHINIDÆ.

_No anal fin; two dorsal fins. Spiracles present. Pectoral fins large,
with the basal portion prolonged forwards, but not grown to the head._

   RHINA.--Head and body depressed, flat; mouth anterior.
   Gill-openings rather wide, lateral, partly covered by the base
   of the pectoral. Spiracles wide, behind the eyes. Teeth conical,
   pointed, distant. Dorsal fins on the tail.

The “Angel-fish,” or “Monk-fish” (_Rh. squatina_), approaches the
Rays as regards general form and habits. Within the temperate and
tropical zones it is almost cosmopolitan, being well known on the
coasts of Europe, eastern North America, California, Japan, South
Australia, etc.; it does not seem to exceed a length of five feet; it
is viviparous, producing about twenty young at a birth.

Extinct forms, closely allied to the “Angel-fish,” are found in the
Oolite, and have been described as _Thaumas_. The carboniferous genus,
_Orthacanthus_, may have been allied to this family, but it was armed
with a spine immediately behind the head.


                     TENTH FAMILY--PRISTIOPHORIDÆ.

_The rostral cartilage is produced, into an exceedingly long, flat
lamina, armed along each edge with a series of teeth_ (saw).

These Sharks resemble so much the common Saw-fishes as to be easily
confounded with them, but their gill-openings are lateral, and not
inferior. They are also much smaller in size, and a pair of long
tentacles are inserted at the lower side of the saw. The four species
known (_Pristiophorus_) occur in the Australian and Japanese seas.

_Squaloraja_, from the Lias, is supposed to have its nearest
affinities to this family.


                          B. BATOIDEI--RAYS.

In the typical Rays the body is excessively depressed, and forms, with
the expanded pectoral fins, a circular or sub-rhomboidal disk, of which
the slender tail appears as a more or less long appendage. In the two
families which we shall place first (_Pristidæ_ and _Rhinobatidæ_),
the general habit of the body still resembles that of the Sharks,
but the gill-openings are ventral, as in the true Rays; the anal fin
is invariably absent, and the dorsal fins, if developed, are placed
on the tail. The mode of life of those fishes is quite in accordance
with the form of their body. Whilst the species with a shark-like body
and muscular tail swim freely through the water, and are capable of
executing rapid and sustained motions, the true Rays lead a sedentary
life, moving slowly on the bottom, rarely ascending to the surface.
Their tail has almost entirely lost the function of an organ of
locomotion, acting in some merely as a rudder. They progress solely by
means of the pectoral fins, the broad and thin margins of which are set
in an undulating motion, entirely identical with that of the dorsal and
anal fins of the _Pleuronectidæ_. They are exclusively carnivorous,
like the Sharks, but unable to pursue and catch rapidly-moving
animals; therefore they feed chiefly on molluscous and crustaceous
animals. However, the colour of their integuments assimilates so
closely that of their surroundings, that other fishes approach them
near enough to be captured by them. The mouth of Rays being entirely
at the lower surface of the head, the prey is not directly seized with
the jaws; but the fish darts over its victim so as to cover and hold it
down with its body, when it is conveyed by some rapid motions to the
mouth.

Rays do not descend to the same depth as Sharks; with one
exception,[37] at least, none have been known to have been caught by a
dredge worked in more than 100 fathoms. The majority are coast fishes,
and have a comparatively limited geographical range, none extending
from the northern temperate zone into the southern. However, some,
if not all the species of the family _Myliobatidæ_, which includes
the giants of this division of Plagiostomes, have a claim of being
included among the Pelagic fishes, as they are frequently met with
in the open ocean at a great distance from the shore. It is probable
that the occurrence of such individuals in the open sea indicates the
neighbourhood of some bank or other comparatively shallow locality.
Many species are exclusively confined to fresh water, and occur far
inland, especially in tropical America.

The majority are oviparous. All have five pairs of gill-openings. The
number of known species is about the same as that of Sharks, viz. 140.


                        FIRST FAMILY--PRISTIDÆ.

_The snout is produced into an exceedingly long flat lamina, armed
with a series of strong teeth along each edge_ (saw).

   PRISTIS.--Body depressed and elongate, gradually passing into
   the strong and muscular tail. Pectoral fins, with the front
   margins quite free, not extending to the head. No tentacles
   below the saw. Teeth in the jaws minute, obtuse. Dorsal fins
   without spine, the first opposite or close to the base of the
   ventrals.

“Saw-fishes.” Abundant in tropical, less so in sub-tropical seas. They
attain to a considerable size, specimens with a saw 6 feet long and 1
foot broad at the base not being of uncommon occurrence. The saw, which
is their weapon of attack, renders them most dangerous to almost all
the other large inhabitants of the ocean. Its endoskeleton consists
of three, sometimes five, rarely four, hollow cylindrical tubes,
placed side by side, tapering towards the end, and incrusted with an
osseous deposit. These tubes are the rostral processes of the cranial
cartilage, and exist in all Rays, though in them they are shorter and
much less developed. The teeth of the saw are implanted in deep sockets
of the hardened integument. The teeth proper, with which the jaws
are armed, are much too small for inflicting wounds or seizing other
animals. Saw-fishes use this weapon in tearing pieces of flesh off
an animal’s body or ripping open its abdomen. The detached fragments
or protruding soft parts are then seized by them and swallowed. Five
distinct species of Saw-fishes are known.

Saws of extinct species have been found in the London clay of Sheppey
and in the Bagshot sands.


                      SECOND FAMILY--RHINOBATIDÆ.

_Tail strong and long, with two well-developed dorsal fins, and a
longitudinal fold on each side; caudal developed. Disk not excessively
dilated, the rayed portion of the pectoral fins not being continued to
the snout._

   RHYNCHOBATUS.--Dorsal fins without spine, the first opposite to
   the ventrals. Caudal fin with the lower lobe well developed.
   Teeth obtuse, granular, the dental surfaces of the jaws being
   undulated.

  [Illustration: Fig. 125.--Dentition of _Rhynchobatus_.]

Two species, _Rh. ancylostomus_ and _Rh. djeddensis_, are very common
on the tropical coasts of the Indian Ocean. They feed on hard-shelled
animals, and attain scarcely a length of 8 feet.

   RHINOBATUS.--Cranial cartilage produced into a long rostral
   process, the space between the process and pectoral fin
   being filled by a membrane. Teeth obtuse, with an indistinct
   transverse ridge. Dorsal fins without spine, both at a great
   distance behind the ventral fins. Caudal fin without lower lobe.

Numerous on the coasts of tropical and sub-tropical seas; about twelve
species. _Trygonorhina_ is an allied genus from South Australia.

The oolitic genus _Spathobatis_ is scarcely distinct from
_Rhinobatus_; and another fossil from Mount Lebanon has been
actually referred to this latter genus. _Trigorhina_ from Monte
Postale must be placed here.


                      THIRD FAMILY--TORPEDINIDÆ.

_The trunk is a broad, smooth disk. Tail with a longitudinal fold
on each side; a rayed dorsal fin is generally, and a caudal always,
present. Anterior nasal valves confluent into a quadrangular lobe.
An electric organ composed of vertical hexagonal prisms between the
pectoral fins and the head._

“Electric Rays.” The electric organs with which these fishes are armed
are large, flat, uniform bodies, lying one on each side of the head,
bounded behind by the scapular arch, and laterally by the anterior
crescentic tips of the pectoral fins. They consist of an assemblage
of vertical hexagonal prisms, whose ends are in contact with the
integuments above and below; and each prism is subdivided by delicate
transverse septa, forming cells, filled with a clear, trembling,
jelly-like fluid, and lined within by an epithelium of nucleated
corpuscles. Between this epithelium and the transverse septa and walls
of the prism there is a layer of tissue on which the terminations
of the nerves and vessels ramify. Hunter counted 470 prisms in each
battery of _Torpedo marmorata_, and demonstrated the enormous
supply of nervous matter which they receive. Each organ receives one
branch of the Trigeminal nerve and four branches of the Vagus, the
former, and the three anterior branches of the latter, being each as
thick as the spinal chord (electric lobes). The fish gives the electric
shock voluntarily, when it is excited to do so in self-defence or
intends to stun or to kill its prey; but to receive the shock the
object must complete the galvanic circuit by communicating with the
fish at two distinct points, either directly or through the medium
of some conducting body. If an insulated frog’s leg touches the fish
by the end of the nerve only, no muscular contractions ensue on the
discharge of the battery, but a second point of contact immediately
produces them. It is said that a painful sensation may be produced
by a discharge conveyed through the medium of a stream of water. The
electric currents created in these fishes exercise all the other known
powers of electricity: they render the needle magnetic, decompose
chemical compounds, and emit the spark. The dorsal surface of the
electric organ is positive, the ventral surface negative.

   [The literature on the electric organ of Torpedo is very
   extensive. Here may be mentioned _Lorenzini_, “Osservazioni
   intorno alle Torpedini,” (1678); _Walsh_, “On the Electric
   Property of the Torpedo,” in Philos. Trans., 1773; _Hunter_,
   “Anatomical Observations on the Torpedo,” _ibid._;
   _Davy_, “Observations on the Torpedo,” in Philos. Trans.,
   1834; _Matteucci_ and _Savi_, “Traité des Phénomènes
   Electro-Physiologiques,” 1844.]

Of the genus _Torpedo_ six species are known, distributed over the
Atlantic and Indian Oceans; three of them are rather common in the
Mediterranean, and one (_T. hebetans_) reaches the south coast of
England. They attain to a width of from two to three feet, and
specimens of that size are able to disable by a single discharge a
full-grown man, and, therefore, may prove dangerous to bathing persons.
Other genera, differing from _Torpedo_ in the position and structure of
some of the fins, are found in other tropical and sub-tropical seas,
viz. _Narcine_, _Hypnos_, _Discopyge_ (Peru), _Astrape_, and _Temera_.
All, like electric fishes generally, have a naked body.

A large fish, of the general appearance of a Torpedo, has been found at
Monte Bolca; and _Cyclobatis_, from the upper cretaceous limestone of
Lebanon, is probably another extinct representative of this family.


                        FOURTH FAMILY--RAJIDÆ.

_Disk broad, rhombic, generally with asperities or spines; tail with
a longitudinal fold on each side. The pectoral fins extend to the
snout. No electric organ; no serrated caudal spine._

   RAJA.--Two dorsal fins on the tail, without spine; tail with
   a rudimentary caudal fin, or without caudal. Each ventral fin
   divided into two by a deep notch. Teeth small, obtuse, or
   pointed. Pectoral fins not extending forwards to the extremity
   of the snout. Nasal valves separated in the middle, where they
   are without a free margin (see Fig. 1, p. 34).

  [Illustration: Fig. 126.--Raja lemprieri, from Tasmania.]

  [Illustration: Fig. 127.--Dermal spines of a male Thornback, Raja
  clavata.]

Of all the genera of _Batoidei_, Rays have the widest geographical
range; they are chiefly inhabitants of temperate seas, and much more
numerous in those of the Northern than of the Southern Hemisphere.
They advance more closely to the Arctic and Antarctic circles than
any other member of this group. More than thirty species are known,
of which the following are found on the British coast:--The Thornback
(_R. clavata_), the Homelyn Ray (_R. maculata_), the Starry Ray (_R.
radiata_), the Sandy Ray (_R. circularis_), the common Skate (_R.
batis_), the Burton Skate (_R. marginata_), and the Shagreen Skate (_R.
fullonica_). Some of these species, especially the Skates, attain a
considerable size, the disk measuring six and even seven feet across.
All are eatable, and some of them regularly brought to market. In the
majority of the species peculiar sexual differences have been observed.
In some, as in the Thornback, all or some of the teeth are pointed
in the male sex, whilst they are obtuse and flat in the female. The
males of all are armed with patches of claw-like spines, retractile in
grooves of the integument, and serially arranged occupying a space on
the upper side of the pectoral fin near the angle of the disk, and
frequently also the sides of the head. In species which are armed with
bucklers or asperities it is the female which is principally provided
with these dermal productions, the male being entirely or nearly
smooth. Also the colour is frequently different in the two sexes.

Other genera of this family are _Psammobatis_, _Sympterygia_, and
_Platyrhina_. Although probably this family was well represented in
cretaceous and tertiary formations, the remains found hitherto are
comparatively few. _Arthropterus_, from the Lias, seems to have been a
true Ray; and dermal spines of a species allied to the Thornback (_Raja
antiqua_) are abundant in the crag deposits of Suffolk and Norfolk.


                       FIFTH FAMILY--TRYGONIDÆ.

_The pectoral fins are uninterruptedly continued to, and confluent
at, the extremity of the snout. Tail long and slender, without lateral
longitudinal folds; vertical fins none, or imperfectly developed, often
replaced by a strong serrated spine._

The “Sting-Rays” are as numerous as the Rays proper, but they inhabit
rather tropical than temperate seas. The species armed with a spine
use it as a weapon of defence, and the wounds inflicted by it are, to
man, extremely painful, and have frequently occasioned the loss of a
limb. We have mentioned above (p. 190) that the danger arises from the
lacerated nature of the wound as well as from the poisonous property of
the mucus inoculated. The spines (Fig. 98, p. 190) are always barbed on
the sides, and may be eight or nine inches long in the larger species.
They are shed from time to time, and replaced by others growing behind
the one in function, as the teeth of the fishes of this order, or as
the fangs of a poisonous snake. Fossil species of _Trygon_ and
_Urolophus_ occur in the tertiary strata of Monte Bolca and Monte
Postale. The genera into which the various species have been divided
are the following:--

   UROGYMNUS.--Tail long, without fin or spine, sometimes with a
   narrow cutaneous fold below. Body densely covered with osseous
   tubercles. Teeth flattened.

Only one species is known (_U. asperrimus_), common in the Indian
Ocean, and with a body from 4 to 5 feet long; the skin is frequently
used for covering shields and the handles of swords and other weapons,
its rough surface offering a firm hold to the hand.

   TRYGON.--Tail very long, tapering, armed with a long
   arrow-shaped barbed spine. Body smooth or with tubercles. Nasal
   valves coalescent into a quadrangular flap. Teeth flattened.

Some twenty-five species are known, one of which (_T. pastinaca_)
extends from the south coast of England and the east coast of North
America through the Atlantic and Indian Ocean to Japan. The majority
of the species belong to the tropical parts of the Indian and Atlantic
Oceans; some inhabit exclusively freshwaters of eastern tropical
America. A closely allied genus is _Tæniura_, with six species.

   UROLOPHUS.--Tail of moderate length, with a distinct rayed
   terminal fin, armed with a barbed spine, without or with a
   rudimentary dorsal fin. Teeth flattened.

Seven species from tropical seas, apparently of small size.

  [Illustration: Fig. 128.--Urolophus cruciatus, from Australia.]

   PTEROPLATEA.--Body at least twice as broad as long; tail very
   short and thin, without or with a rudimentary fin, and with a
   serrated spine. Teeth very small, uni- or tri-cuspid.

Six species from temperate and tropical seas.


                      SIXTH FAMILY--MYLIOBATIDÆ.

_The disk is very broad, in consequence of the great development of
the pectoral fins, which, however, leave the sides of the head free,
and reappear at the extremity of the snout as a pair of detached
(cephalic) fins. Viviparous._

“Devil-fishes,” “Sea-devils,” or “Eagle-rays.” Generally of large
size, inhabiting temperate and tropical seas. Some genera possess a
pair of singular cephalic processes, which generally project in a
direction parallel to the longitudinal axis of the body, but are said
to be flexible in the living fish, and used for scooping food from the
bottom and conveying it to the mouth. In all the species the dentition
consists of perfectly flat molars, forming a kind of mosaic pavement in
both the upper and lower jaws: a most perfect mechanical arrangement
for crushing alimentary substances.

  [Illustration: Fig. 129.--Jaws of an Eagle-Ray, _Myliobatis
  aquila._]

   MYLIOBATIS.--Teeth sexangular, large, flat, tessellated, those
   in the middle much broader than long; several narrower series
   on each side. Tail very long and thin, with a dorsal fin near
   its root; generally a serrated spine behind the fin.

Seven species are known, two of which are European, one (_M. aquila_)
being almost cosmopolitan, and occasionally found on the British coast.
The young differ much from the adult, having no median series of larger
teeth, but all the teeth of equal size and regularly sexangular. Also
the tail is much longer in young examples than in old ones, and the
coloration more ornamental. Teeth of species very closely allied to, or
perhaps even identical with, existing species, are found in tertiary
formations.

   AËTOBATIS.--Form of the head, body, and tail as _Myliobatis_.
   The nasal valves remain separate, each forming a long flap.
   The lower dental lamina projects beyond the upper. Teeth flat,
   broad, forming a single series, equivalent to the median series
   of _Myliobatis_, there being no small lateral teeth.

  [Illustration: Fig. 130.--Aëtobatis narinari.]

One species only (_A. narinari_) which is found in almost all tropical
seas, and of exceedingly common occurrence in the Atlantic and Indian
Oceans; it does not seem to grow to a very large size (perhaps not
exceeding 5 feet in width), and is readily recognised by numerous round
bluish-white spots, with which the back is ornamented. Fossils of this
genus occur in the English Eocenes and the Swiss Molasse.

  [Illustration: Fig. 131.--Aëtobatis subarcuatus, from
  Bracklesham.]

RHINOPTERA.--The cephalic appendages are bent inwards, and situated
at the lower side of the snout. Nasal valves confluent into a broad
flap, with free margin. Teeth broad, flat, tessellated, in five or
more series, the middle being the broadest, and the others decreasing
in width outwards. Tail very slender, with a dorsal fin before the
serrated spine.

  [Illustration: Fig. 132.--Rhinoptera woodwardi; fossil.]

  [Illustration: Fig. 133.--Rhinoptera polyodon.]

Seven species from tropical and sub-tropical seas are known; of
_Rhinoptera polyodon_ nothing is known except the jaws; and as its
dentition is very peculiar, no opportunity should be lost of obtaining
and preserving entire animals. Teeth very similar to those of existing
species, and described as _Zygobatis_, occur in the Norwich Crag
and in Miocene formations of Switzerland.

   DICEROBATIS (CEPHALOPTERA).--Cephalic appendages pointing
   straight forwards or inwards. Nostrils widely separated from
   each other. Mouth inferior, wide. Both jaws with very numerous
   and very small flat or tubercular teeth. Tail very slender,
   with a dorsal fin between the ventrals, and with or without a
   serrated spine.

   CERATOPTERA.--Cephalic appendages pointing forwards or inwards.
   Mouth anterior; wide. Teeth in the lower jaw only, very small.
   Tail very slender, with a dorsal fin between the ventrals and
   without spine.

  [Illustration: Fig. 134.--Dicerobatis draco, from Misol.]

The species of these two last genera are not yet well distinguished;
about five of _Dicerobatis_ and two of _Ceratoptera_ are known from
tropical and temperate seas, but their occurrence in the latter is
rather sporadic. Some of them, if not all, attain an enormous size.
One mentioned by Risso, taken off Messina, weighed 1250 pounds.
Several observers speak of having seen them in pairs, the male being
usually the smaller. Of a pair mentioned by Risso the female was first
taken, and the male remained hovering about the boat for three days,
and was afterwards found floating dead on the surface. Still larger
individuals, but of uncertain species, are mentioned by Lacépède, who
says that one taken at Barbadoes required seven yoke of oxen to draw
it. A sketch of another, which was said to be twenty feet long, was
sent to Lacépède; and Sonnini speaks of one which appeared to him to be
longer and wider than the ship in which he was sailing. A fœtus taken
from the uterus of the mother captured at Jamaica, and preserved in
the British Museum, is five feet broad, and weighed twenty pounds. The
mother measured fifteen feet in width as well as in length, and was
between three and four feet thick. The capture of “Devil-fishes” of
such large size is attended with danger, as they not rarely attack and
capsize the boat. They are said to be especially dangerous when they
accompany their young, of which they bring forth one only at a time.


                    SECOND SUB-ORDER--HOLOCEPHALA.

_One external gill-opening only, covered by a fold of the skin, which
encloses a rudimentary cartilaginous gill-cover; four branchial clefts
within the gill-cavity. The maxillary and palatal apparatus coalescent
with the skull._

This suborder is represented in the living fauna by one family only,
_Chimæridæ_; it forms a passage to the following order of fishes, the
Ganoids. In external appearance, and with regard to the structure of
their organs of propagation, the Chimæras are Sharks (See Fig. 96, p.
184). The males are provided with “claspers” in connection with the
ventral fins, and the ova are large, encased in a horny capsule, and
few in number; and there is no doubt that they are impregnated within
the oviduct, as in Sharks. Chimæras are naked, but, as in _Scylliidæ_,
very young individuals possess a series of small “placoid” spines,
which occupy the median line of the back, and remind us of similar
dermal productions in the Rays. The males, besides, are provided with
a singular erectile appendage, spiny at its extremity, and received
in a groove on the top of the head. On the other hand, the relations
of the Chimæras to the Ganoid, and, more especially, Dipnoous type
become manifest in their notochordal skeleton and continuity of
cranial cartilage. The spine in front of the first dorsal fin is
articulated to the neural apophysis, and not merely implanted in the
soft parts, and immovable as in Sharks. A cartilaginous operculum
makes its appearance, and the external gill-opening is single. The
dentition is that of a Dipnoid, each “jaw” being armed with a pair of
broad dental plates, with the addition of a pair of smaller cutting
teeth in the upper “jaw.” Fossils of similar dental combination are
not rare in strata, commencing from the Lias and the bottom of the
Oolitic series; but it is impossible to decide in every case whether
the fossil should be referred to the Holocephalous or Dipnoous type.
According to Newberry, Chimæroid fishes commence in the Devonian with
_Rhynchodus_, the remains of which were discovered by him in Devonian
rocks of Ohio. Undoubted Chimæroids are _Elasmodus_, _Psaliodus_,
_Ganodus_, _Ischyodus_, _Edaphodon_, and _Elasmognathus_, principally
from mesozoic and tertiary formations. Very similar fossils occur
in the corresponding strata of North America. A single species of
_Callorhynchus_ has been discovered by H. Hector in the Lower Greensand
of New Zealand.

The living Chimæras are few in number, and remain within very moderate
dimensions, probably not exceeding a length of five feet, inclusive
of their long filamentous, diphycercal tail. They are referred to two
genera.

   CHIMÆRA.--Snout soft, prominent, without appendage. The dorsal
   fins occupying the greater part of the back, anterior with
   a very strong and long spine. Longitudinal axis of the tail
   nearly the same as that of the trunk, its extremity being
   provided with a low fin above and below, similar in form to a
   dorsal and anal fin. Anal fin very low.

Three species are known: _Ch. monstrosa_, from the coasts of Europe and
Japan and the Cape of Good Hope; _Ch. colliei_ from the west coast of
North America; and _Ch. affinis_ from the coast of Portugal. (See Fig.
96, p. 184.)

   CALLORHYNCHUS.--Snout with a cartilaginous prominence,
   terminating in a cutaneous flap. Two dorsal fins, the anterior
   with a very strong and long spine. Extremity of the tail
   distinctly turned upwards, with a fin along its lower edge, but
   without one above. Anal fin close to the caudal, short and deep.

One species (_C. antarcticus_) is common in the Southern temperate
zone. Cunningham describes the egg (see Fig. 81, p. 169), as being of
a dark greenish-black colour, and, in general, measuring from eight
to nine or even ten inches in length, by about three in breadth. It
consists of a central, somewhat spindle-shaped convex area (between
the horny walls of which the young fish lies), surrounded by a broad
plicated margin, which is fringed at the edge, and covered on the under
surface with fine light brownish-yellow hairs.


                        SECOND ORDER--GANOIDEI.

_Skeleton cartilaginous or ossified. Body with medial and paired
fins, the hinder pair abdominal. Gills free, rarely partially attached
to the walls of the gill-cavity. One external gill-opening only on
each side; a gill-cover. Air-bladder with a pneumatic duct. Ova small,
impregnated after exclusion. Embryo sometimes with external gills._

To this order belong the majority of the fossil fish remains of
palæozoic and mesozoic age, whilst it is very scantily represented
in the recent fauna, and evidently verging towards total extinction.
The knowledge of the fossil forms, based on mere fragments of the
hard parts of the body only, is very incomplete, and therefore their
classification is in a most unsatisfactory state. In the following
pages only the most important groups will be mentioned.

   [For a study of details we have to refer to _Agassiz_, “Poissons
   Fossiles;” _Owen_, “Palæontology,” Edinb. 1861, 8vo; _Huxley_,
   “Preliminary Essay upon the Systematic Arrangement of the Fishes
   of the Devonian Epoch,” in Mem. Geolog. Survey, Dec. 10; Lond.
   1861, and “Illustrations of the Structure of Crossopterygian
   Ganoids,” _ibid._ December 12, 1866; _Traquair_, “The Ganoids of
   the British Carboniferous Formations,” part I. “Palæoniscidæ.”
   Palæontogr. Soc. Lond. 1877.]

Eight suborders may be distinguished at present.


                     FIRST SUB-ORDER--PLACODERMI.

_Extinct. The head and pectoral region of the body encased in great
bony, sculptured plates, with dots of enamel; the remainder of the body
naked, or with ganoid scales; skeleton notochordal._

Comprises the oldest vertebrate remains, from Devonian and
Carboniferous formations. _Pterichthys_: (Figs. 135 and 136), tail
tapering, covered with small ganoid scales, without caudal fin; the
cephalic shield was probably moveably joined to the cuirass of the
trunk, and both were composed of several pieces; the abdominal shield
consisted of one single median plate, and two pairs of lateral plates,
a third small pair being sometimes observed detached in front of the
anterior pair; pectoral exceedingly long, consisting of two pieces
movably connected with each other; tail scaly, and short; a small
dorsal fin placed on the tail; a pair of small ventrals; jaws small,
with confluent denticles. Several species have been distinguished
in remains found in the strata of Caithness and other localities in
Scotland. _Coccosteus_ (Fig. 137, p. 354): all the bony plates are
firmly united, no pectoral spines; tail naked and long; a dorsal and
anal fin supported by interneural and interhæmal spines. Dentition
unknown. _Dinichthys_: a gigantic fish from the Devonian of North
America (estimated at from 15 to 18 feet in length), with the dermal
covering very similar to that of Coccosteus, but with a simple arched
dorsal shield. As in this latter genus the caudal extremity does not
possess external or internal bony parts, and the ventral plastron
of both genera corresponds in every particular; the dentition is so
singularly like that of Lepidosiren, that Newberry (Geolog. Survey of
Ohio, vol. ii. part 2) considers this genus to be in genetic relation
to the Dipnoi. The following genera have been united in a separate
family, _Cephalaspidæ_; viz. _Cephal__aspis_: head covered by a
continuous shield with tubercular surface, produced into a horn at each
posterior corner; a median dorsal backward prolongation bears a spine;
heterocercal. _Auchenaspis_ and _Didymaspis_: allied to the preceding,
but with the cephalic shield divided into a larger anterior and smaller
posterior piece. _Pteraspis_: with the cephalic shield finely striated
or grooved, composed of seven pieces. _Scaphaspis_ and _Cyathaspis_:
with the surface of the head-shield similarly sculptured as in
_Pteraspis_, but simple in the former, and composed of four pieces in
the latter. _Astrolepis_: attained to the gigantic size of between
twenty and thirty feet; its mouth was furnished with two rows of teeth,
of which the outer ones were small, the inner much larger.

   [See Ray Lankester, A. Monograph of the Fishes of the Old Red
   Sandstone of Britain. Part I. Cephalaspidæ. Lond. 1868 and 1870.
   4to.]

  [Illustration: Fig. 135.--Dorsal surface of Pterichthys, after
  Pander. _d_, Dorsal fin; _c_, pectoral member; 2–10,
  head-bucklers; 11–13, dorsal bucklers.]

  [Illustration: Fig. 136.--Ventral aspect of Pterichthys, after
  Pander. 15, mandible (?); 16–21, ventral bucklers.]

  [Illustration: Fig. 137.--Coccosteus, after Pander. _A_, Anal
  fin; _D_, Dorsal fin; _C_, Heterocercal tail; _c_, notochord;
  _n_, neurals; _h_, hæmals; 6–24, bucklers.]


                    SECOND SUB-ORDER--ACANTHODINI.

Extinct. _Body oblong, compressed, covered with shagreen; skull
not ossified; caudal heterocercal. Large spines, similar to those of
Chondropterygians, in front of some of the median and paired fins.
The spines are imbedded between the muscles, and not provided with a
proximal joint._

_Acanthodes_, _Chiracanthus_, from Devonian and Carboniferous
formations.


                       THIRD SUB-ORDER--DIPNOI.

_Nostrils two pairs, more or less within the mouth; limbs with
an axial skeleton. Lungs and gills. Skeleton notochordal. No
branchiostegals._[38]


                        FIRST FAMILY--SIRENIDÆ.

_Caudal fin diphycercal; no gular plates; scales cycloid. A pair of
molars, above and below, and one pair of vomerine teeth._

   LEPIDOSIREN.--Body eel-shaped, with one continuous vertical fin.
   Limbs reduced to cylindrical filaments, without fringe. Vomerine
   teeth conical, pointed. Each dental lamina or molar with strong
   cusps, supported by vertical ridges. No external branchial
   appendages; five branchial arches, with four intervening clefts.
   Conus arteriosus with two longitudinal valves. Ovaries closed
   sacs.

One species only is known from the system of the River Amazons (_L.
paradoxa_). It must be very locally distributed, as but a few
specimens have been brought to Europe, and all recent endeavours to
obtain others have been unsuccessful. Natterer, by whom this most
interesting fish was discovered, states that he obtained two specimens,
one on the Madeira River, near Borba; the other in a backwater of the
Amazons, above Villa Nova. The natives of the former place called it
Carámurú, and considered it very scarce. The larger individual was
nearly four feet long. It is said to produce a sound not unlike that
of a cat, and to feed on the roots of mandioca and other vegetables.
But, to judge from the dentition, this fish is much more likely to be
carnivorous, like the following. It is one of the greatest desiderata
of Natural History Collections.

   [Natterer, “Annalen des Wiener Museum’s,” 1839, ii.; Bischoff.
   “Annales des Sciences Naturelles,” 1840. xiv.]

   PROTOPTERUS.--Very similar in the general form of the body and
   dentition to _Lepidosiren_. Pectoral and ventral filaments with
   a fringe containing rays. Three small branchial appendages
   above the small gill-opening; six branchial arches, with five
   intervening clefts. Conus arteriosus with two longitudinal
   valves. Ovaries closed sacs.

_Protopterus annectens_ is the “Lepidosiren” which is commonly found in
Zoological collections. It is usually imported from the west coast of
Africa, where it abounds in many localities; but it is spread over the
whole of tropical Africa, and forms in many districts of the central
parts a regular article of food.

  [Illustration: Fig. 138.--Protopterus annectens. _g_,
  Branchial filaments; _v_, vent.]

During the dry season, specimens living in shallow waters which
periodically dry up, form a cavity in the mud, the inside of which they
line with a protecting capsule of mucus, and from which they emerge
again when the rains refill the pools inhabited by them. Whilst they
remain in this torpid state of existence, the clay-balls containing
them are frequently dug out, and if the capsules are not broken, the
fishes imbedded in them can be transported to Europe, and released
by being immersed in slightly tepid water. _Protopterus_ is
exclusively carnivorous, feeding on water-insects, frogs, and fishes,
and attains a length of six feet.

    [Owen, “Trans. Linn. Soc.” 1841, xviii.]

   CERATODUS.--Body elongate, compressed, with one continuous
   vertical fin. Limbs paddle-shaped, with broad, rayed fringe.
   Vomerine teeth incisor-like; molars with flat, undulated
   surface, and lateral prongs. No external branchial appendages.
   Conus arteriosus with transverse series of valves. Ovaries
   transversely lamellated.[39]

  [Illustration: Fig. 139.--_Ceratodus miolepis._]

Two species, _C. forsteri_ and _C. miolepis_, are known from fresh
waters of Queensland. The specimens hitherto obtained have come from
the Burnett, Dawson, and Mary rivers, some from the fresh waters of
the upper parts, others from the lower brackish portions. The fish is
said to attain to a weight of twenty pounds and to a length of 6 feet.
Locally, the settlers call it “Flat-head,” “Burnett- or Dawson-Salmon,”
and the aborigines “Barramunda,” a name which they appear to apply
also to other large-scaled freshwater fishes, as the Osteoglossum
leichardti. In the stomach there is generally found an enormous
quantity of the leaves of plants growing on the banks of rivers,
evidently eaten after they had fallen into the water and when in a
decomposing condition. The flesh of the fish is salmon-coloured, and
much esteemed as food.

The Barramunda is said to be in the habit of going on land, or at least
on mud-flats; and this assertion appears to be borne out by the fact
that it is provided with a lung. However, it is much more probable
that it rises now and then to the surface of the water in order to
fill its lung with air, and then descends again until the air is so
much deoxygenised as to render a renewal of it necessary. It is also
said to make a grunting noise, which may be heard at night for some
distance. This noise is probably produced by the passage of the air
through the œsophagus when it is expelled for the purpose of renewal.
As the Barramunda has perfectly developed gills, beside the lung, we
can hardly doubt that, when it is in water of normal composition,
and sufficiently pure to yield the necessary supply of oxygen, these
organs are sufficient for the purpose of breathing, and that the
respiratory function rests with them alone. But when the fish is
compelled to sojourn in thick muddy water charged with gases, which are
the products of decomposing organic matter (and this must be the case
very frequently during the droughts which annually exhaust the creeks
of tropical Australia), it commences to breathe air with its lung in
the way indicated above. If the medium in which it happens to be is
perfectly unfit for breathing the gills cease to have any function;
if only in a less degree the gills may still continue to assist in
respiration. The Barramunda, in fact, can breathe by either gills or
lungs alone, or by both simultaneously. It is not probable that it
lives freely out of the water, its limbs being much too flexible for
supporting the heavy and unwieldy body, and too feeble generally to be
of much use in locomotion on land. However, it is quite possible that
it is occasionally compelled to leave the water, although we cannot
believe that it can exist without it in a lively condition for any
length of time.

Of its propagation or development we know nothing, except that it
deposits a great number of eggs of the size of those of a newt, and
enveloped in a gelatinous case. We may infer that the young are
provided with external gills, as in Protopterus and Polypterus.

  [Illustration: Fig. 140.--Tooth of fossil _Ceratodus_ from
  Aust., near Bristol, natural size.]

The discovery of _Ceratodus_ does not date farther back than the year
1870, and proved to be of the greatest interest, not only on account
of the relation of this creature to the other living _Dipnoi_ and
_Ganoidei_, but also because it threw fresh light on those singular
fossil teeth which are found in strata of Triassic and Jurassic
formations in various parts of Europe, India, and America. These teeth,
of which there is a great variety with regard to general shape and
size, are sometimes two inches long, much longer than broad, depressed,
with a flat or slightly undulated, always punctated crown, with one
margin convex, and with from three to seven prongs projecting on the
opposite margin.

  [Illustration: Fig. 141.--Dipterus macrolepidotus.]


                   SECOND FAMILY--CTENODODIPTERIDÆ.

_Caudal fin heterocercal. Gular plates. Scales cycloid. Two pairs of
molars and one pair of vomerine teeth._

Extinct. _Dipterus_ (_Ctenodus_), _Heliodus_ from Devonian strata.


                    THIRD FAMILY--PHANEROPLEURIDÆ.

_Caudal fin diphycercal; vertical fin continuous. Gular plates.
Scales cycloid. Jaws with a series of minute conical teeth on the
margin._

Extinct. _Phaneropleuron_ from Devonian formations, and the
carboniferous _Uronemus_ are probably generically identical.


                    FOURTH SUB-ORDER--CHONDROSTEI.

_Skeleton notochordal; skull cartilaginous, with dermal ossifications;
branchiostegals few in number or absent. Teeth minute or absent.
Integuments naked or with bucklers. Caudal fin heterocercal, with
fulcra. Nostrils double, in front of the eyes._


                      FIRST FAMILY--ACIPENSERIDÆ.

_Body elongate, sub-cylindrical, with five rows of osseous bucklers.
Snout produced, subspatulate or conical, with the mouth at its lower
surface, small, transverse, protractile, toothless. Four barbels in a
transverse series on the lower side of the snout. Vertical fins with
a single series of fulcra in front. Dorsal and anal fins approximate
to the caudal. Gill-membranes confluent at the throat and attached to
the isthmus. Branchiostegals none. Gills four; two accessory gills.
Air-bladder large, simple, communicating with the dorsal wall of the
œsophagus._

  [Illustration: Fig. 142.--Tail of Acipenser. _a_, Fulcra;
  _b_, osseous bucklers.]

Sturgeons are, perhaps, the geologically youngest Ganoids, evidence
of their existence not having been met with hitherto in formations
of older date than the Eocene clay of Sheppey. They are exclusively
inhabitants of the temperate zone of the Northern Hemisphere, being
either entirely confined to fresh water, or passing, for the purpose of
spawning, a part of the year in rivers. They grow to a large size, and
are the largest fishes of the fresh waters of the Northern Hemisphere,
specimens 10 feet long being of common occurrence. The ova are very
small, and so numerous that one female has been calculated to produce
about three millions at one season; therefore their propagation, as
well as their growth, must be very rapid; and although in many rivers
their number is annually considerably thinned by the systematic manner
in which they are caught when they ascend the rivers in shoals from the
sea, no diminution has been observed. Wherever they occur they prove
to be most valuable on account of their wholesome flesh. In Russia,
besides, two not unimportant articles of trade are obtained from them,
viz. Caviare, which is prepared from their ovaries, and Isinglass,
which is made from the inner coats of their air-bladder. True Sturgeons
are divided into two genera, _Acipenser_ and _Scaphirhynchus_.

   ACIPENSER.--The rows of osseous bucklers are not confluent
   on the tail. Spiracles present. Caudal rays surrounding the
   extremity of the tail.

About twenty different species of Sturgeons may be distinguished from
European, Asiatic, and American rivers. The best known are the Sterlet
(_A. ruthenus_) from Russian rivers, celebrated for the excellency of
its flesh, but rarely exceeding a length of three feet; the Californian
Short-snouted Sturgeon (_A. brachyrhynchus_); the Hausen (_A. huso_),
from rivers, falling into the Black Sea and the Sea of Azow (rare
in Mediterranean), sometimes 12 feet long, and yielding an inferior
kind of isinglass; the Chinese Sturgeon (_A. sinensis_); the Common
Sturgeon of the United States (_A. maculosus_), which sometimes crosses
the Atlantic to the coasts of Great Britain; Güldenstædt’s Sturgeon
(_A. güldenstædtii_), common in European and Asiatic rivers, which
yields more than one-fourth of the caviare and isinglass exported from
Russia; the Common Sturgeon of Western Europe (_A. sturio_), which
attains to a length of 18 feet, and has established itself also on the
coasts of Eastern North America.

   SCAPHIRHYNCHUS.--Snout spatulate; posterior part of the tail
   attenuated and depressed, so that it is entirely enveloped by
   the osseous scutes. Spiracles none. The caudal rays do not
   extend to the extremity of the tail, which terminates in a
   filament.

Four species are known: one (_S. platyrhynchus_) from the
river-system of the Mississippi, and the three others from Central
Asia; all are exclusively freshwater fishes; their occurrence in so
widely distant rivers is one of the most striking instances by which
the close affinity of the North American and North Asiatic faunas is
proved.


                     SECOND FAMILY--POLYODONTIDÆ.

_Body naked, or with minute stellate ossifications. Mouth lateral,
very wide, with minute teeth in both jaws. Barbels none. Caudal fin
with fulcra. Dorsal and anal fins approximate to the caudal. Four gills
and a half; no opercular gill or pseudobranchia._

   POLYODON (SPATULARIA).--The snout is produced into an
   exceedingly long, shovel-like process, thin and flexible on
   the sides. Spiracles present. Gill-cover terminating in a very
   long tapering flap. One broad branchiostegal. Each branchial
   arch with a double series of very long, fine, and numerous
   gill-rakers, the two series being divided by a broad membrane.
   Air-bladder cellular. Upper caudal fulcra narrow, numerous.

The single species, _P. folium_, occurs in the Mississippi, and grows
to a length of about six feet, of which the rostral shovel takes about
one-fourth; in young examples it is comparatively still longer.

   PSEPHURUS differs from _Polyodon_ in having the rostral
   process less depressed and more conical. The gill-rakers are
   comparatively short, in moderate number, and distant from one
   another. Upper caudal fulcra enormously developed, and in small
   number (six).

_Psephurus gladius_ inhabits the Yan-tse-Kiang and Hoangho, the
distribution of the _Polyodontidæ_ being perfectly analogous to
that of _Scaphirhynchus_. It grows to an immense size, specimens
of 20 feet in length being mentioned by Basilewsky. The function of the
rostral process in the economy of these fishes is not yet sufficiently
explained. Martens believes that it serves as an organ of feeling,
the water of those large Asiatic and American rivers being too turbid
to admit of the Sturgeon seeing its prey, which consists of other
fishes. The eyes of _Psephurus_, as well as _Polyodon_, are
remarkably small. Both fishes are used as food.

  [Illustration: Fig. 143.--Psephurus gladius.]

Allied to the _Polyodontidæ_, and likewise provided with a
paddle-shaped production of the fore part of the head, is the fossil
genus _Chondrosteus_, remains of which occur in the Lias.


                    FIFTH SUB-ORDER--POLYPTEROIDEI.

_Paired fins with axial skeleton, fringed; dorsal fins two or more.
Branchiostegals absent, but generally gular plates. Vertebral column
diphycercal or heterocercal. Body scaly._


                      FIRST FAMILY--POLYPTERIDÆ.

_Scales ganoid; fins without fulcra. A series of dorsal spines, to
each of which an articulated finlet is attached; anal placed close to
the caudal fin, the vent being near the end of the tail. Abdominal
portion of the vertebral column much longer than the caudal._

   POLYPTERUS.--Teeth rasp-like, in broad bands in the jaws, on
   the vomer and palatine bones; jaws with an outer series of
   closely-set, larger, pointed teeth. Caudal fin surrounding the
   extremity of the vertebral column; ventral fins well developed.
   A spiracle on each side of the parietal, covered with an
   osseous plate. A single large gular plate. Air-bladder double,
   communicating with the ventral wall of the pharynx.

  [Illustration: Fig. 144.--Polypterus bichir.]

This Ganoid is confined to tropical Africa, occurring in abundance in
the rivers of the west coast and in the Upper Nile; but it has not
been found in the river-systems belonging to the Indian Ocean. It is
scarce in the Middle and Lower Nile, and the specimens found below the
Cataracts have been carried down, from southern latitudes, and do not
propagate their species in that part of the river. There is only one
species known, _Polypterus bichir_ (“Bichir” being its vernacular
name in Egypt), which varies in the number of the dorsal finlets,
the lowest being eight, the highest eighteen. It attains to a length
of four feet. Nothing is known of its mode of life, and observations
thereon are very desirable.

   CALAMOICHTHYS.--Distinguished from _Polypterus_ by its greatly
   elongate form, and the absence of ventral fins.

_C. calabaricus_, a dwarf form from Old Calabar.


                    SECOND FAMILY--SAURODIPTERIDÆ.

_Scales ganoid, smooth like the surface of the skull. Two dorsal fins;
paired fins obtusely lobate. Teeth conical. Caudal heterocercal._

Extinct. _Diplopterus_, _Megalichthys_, and _Osteolepis_ from Devonian
and Carboniferous formations.


                     THIRD FAMILY--COELACANTHIDÆ.

_Scales cycloid. Two dorsal fins, each supported by a single
two-pronged interspinous bone; paired fins obtusely lobate. Air-bladder
ossified; notochord persistent, diphycercal._

Extinct. _Coelacanthus_ from carboniferous strata; several other
genera, from the coal formations to the chalk, have been associated
with it--_Undina_, _Graphiurus_, _Macropoma_, _Holophagus_,
_Hoplopygus_, _Rhizodus_.


                     FOURTH FAMILY--HOLOPTYCHIIDÆ.

_Scales cycloid or ganoid, sculptured. Two dorsal fins; pectorals
narrow, acutely lobate; dentition dendrodont._

Extinct. In this family a peculiar type of dentition is found--the
jaws are armed with two kinds of teeth, small ones serially arranged,
and much larger fang-like teeth disposed at long intervals. Both kinds
show at their base in transverse sections a labyrinthic complexity
of structure, numerous fissures radiating from the central mass of
vasodentine which fills up the pulp cavity, and sending off small
ramifying branches. Genera belonging to this family are _Holoptychius_,
_Saurichthys_, _Glyptolepis_, _Dendrodus_, _Glyptolaemus_,
_Glyptopomus_, _Tristichopterus_, _Gyroptychius_, _Strepsodus_, from
Devonian and Carboniferous strata.


                   SIXTH SUB-ORDER--PYCNODONTOIDEI.

_Body compressed, high and short or oval, covered with rhombic scales
arranged in decussating pleurolepidal lines. Notochord persistent.
Paired fins without axial skeleton. Teeth on the palate and hinder part
of the lower jaw molar-like. Branchiostegals, but no gular plates._

Extinct. The regular lozenge-shaped pattern of the integuments of these
fishes is described by Sir P. Egerton thus: “Each scale bears upon its
inner anterior margin a thick solid bony rib, extending upwards beyond
the margin of the scale, and sliced off obliquely, above and below, on
opposite sides, for forming splices with the corresponding processes
of the adjoining scales. These splices are so closely adjusted that,
without a magnifying power or an accidental dislocation, they are not
perceptible. When _in situ_, and seen internally, these continuous
lines decussate with the true vertebral apophyses.” In some genera the
“pleurolepidal” lines are confined to the anterior part of the side.


                      FIRST FAMILY--PLEUROLEPIDÆ.

_Homocercal. Body less high. Fins with fulcra._

_Pleurolepis_ and _Homoeolepis_ from the Lias.


                     SECOND FAMILY--PYCNODONTIDÆ.

_Homocercal. The neural arches and ribs are ossified; the roots of
the ribs are but little expanded in the older genera, but enlarged in
the tertiary forms, so as to simulate vertebræ. Paired fins not lobate.
Obtuse teeth on the palate and the sides of the mandible; maxilla
toothless; incisor-like teeth in the intermaxillary and front of the
mandible. Fulcra absent in all the fins._

These fishes abound in Mesozoic and Tertiary formations. _Gyrodus_,
_Mesturus_, _Microdon_, _Coelodus_, _Pycnodus_, _Mesodon_, are some of
the genera distinguished by palæontologists. (See Fig. 102, p. 201.)


                  SEVENTH SUB-ORDER--LEPIDOSTEOIDEI.

_Scales ganoid, rhombic; fins generally with fulcra; paired fins
not lobate. Præ- and inter-operculum developed; generally numerous
branchiostegals, but no gular plate._


                      FIRST FAMILY--LEPIDOSTEIDÆ.

_Scales ganoid, lozenge-shaped. Skeleton completely ossified;
vertebræ convex in front and concave behind. Fins with fulcra; dorsal
and anal composed of articulated rays only, placed far backwards, close
to the caudal. Abdominal part of the vertebral column much longer
than caudal. Branchiostegals not numerous, without enamelled surface.
Heterocercal._

   _Lepidosteus._--Body elongate, sub-cylindrical; snout elongate,
   spatulate, or beak-shaped; cleft of the mouth wide; both jaws
   and palate armed with bands of rasp-like teeth and series
   of larger conical teeth. Four gills; no spiracles; three
   branchiostegals. Air-bladder cellular, communicating with the
   pharynx.

  [Illustration: Fig. 145.--Lepidosteus viridis.]

Fishes of this genus existed already in Tertiary times; their remains
have been found in Europe as well as North America. In our period
they are limited to the temperate parts of North America, Central
America, and Cuba. Three species can be distinguished which attain
to a length of about six feet. They feed on other fishes, and their
general resemblance to a pike has given to them the vernacular names of
“Gar-Pike,” or “Bony Pike.”


                        SECOND FAMILY--SAURIDÆ.

_Body oblong, with ganoid scales; vertebræ not completely ossified;
termination of the vertebral column homocercal; fins generally with
fulcra. Maxillary composed of a single piece; jaws with a single series
of conical pointed teeth. Branchiostegals numerous, enamelled, the
anterior broad gular plates._

Extinct. Numerous genera occur in Mesozoic formations; one with the
widest range is _Semionotus_, with distichous fulcra, from the Lias and
Jura; _Eugnathus_, with large posteriorly serrated scales, and fulcra
on nearly all fins; _Cephenoplosus_ from the Upper Lias; _Macrosemius_
from the Oolite; _Propterus_, _Ophiopsis_, _Pholidophorus_,
_Pleuropholis_, _Pachycormus_, _Oxygnathus_, _Ptycholepis_, _Conodus_,
_Eulepidotus_, _Lophiostomus_, etc.


                      THIRD FAMILY--STYLODONTIDÆ.

_Body rhombic or ovate, with ganoid scales; vertebræ not completely
ossified; termination of the vertebral column homocercal; fins with
fulcra. Maxillary composed of a single piece; jaws with several series
of teeth, the outer ones equal, styliform. Dorsal fin very long,
extending to the caudal. Branchiostegals numerous._

Extinct. _Tetragonolepis_ from the Lias (see Fig. 103, p. 207).


                     FOURTH FAMILY--SPHÆRODONTIDÆ.

_Body oblong, with rhombic ganoid scales; vertebræ ossified, but not
completely closed; homocercal; fins with fulcra. Maxillary composed of
a single piece; teeth in several series, obtuse; those on the palate
globular. Dorsal and anal fins short. Branchiostegals._

Extinct. The type genus of this family is _Lepidotus_, so named from
its large rhombic, dense, and polished scales. The dorsal is opposite
to the anal, and all the fins are provided with a double row of fulcra.
This genus ranges from the Lias to the Chalk; one species would seem
to have survived into tertiary times, if it should not prove to be a
_Lepidosteus_.


                    FIFTH FAMILY--ASPIDORHYNCHIDÆ.

_Body elongate, with ganoid scales; jaws prolonged into a beak;
termination of the vertebral column homocercal. Fins with fulcra;
a series of enlarged scales along the side of the body. Dorsal fin
opposite to the anal._

  [Illustration: Fig. 146.--Aspidorhynchus fisheri, from the
  Purbeck beds; _m_, mandible; _a_, presymphyseal bone.]

Extinct; mesozoic. _Aspidorhynchus_ has the upper jaw longer than the
lower; very peculiar is the occurrence of a single, solid, conical
bone, situated in front of the symphysis of the lower jaw, to which it
is joined by a suture. _Belonostomus_ with both jaws of equal length.


                      SIXTH FAMILY--PALÆONISCIDÆ.

_Body fusiform, with rhombic ganoid scales. Notochord persistent,
with the vertebral arches ossified. Heterocercal. All the fins with
fulcra; dorsal short. Branchiostegals numerous, the foremost pair
forming broad gulars. Teeth small, conical, or cylindrical._

Extinct. Many genera are known; from the Old Red
Sandstone--_Chirolepis_ and _Acrolepis_; from Carboniferous
rocks--_Cosmoptychius_, _Elonichthys_, _Nematoptychius_,
_Cycloptychius_, _Microconodus_, _Gonatodus_, _Rhadinichthys_,
_Myriolepis_, _Urosthenes_; from the Permian--_Rhabdolepis_,
_Palæoniscus_, _Amblypterus_ and _Pygopterus_; from the
Lias--_Centrolepis_, _Oxygnathus_, _Cosmolepis_, and _Thrissonotus_.

   [See Traquair, “The Ganoid Fishes of the British Carboniferous
   Formations.” Part I. _Palæoniscidæ._]


                     SEVENTH FAMILY--PLATYSOMIDÆ.

_Body generally high, compressed, covered with rhombic ganoid
scales arranged in dorso-ventral bands. Notochord persistent, with
the vertebral arches ossified. Heterocercal; fins with fulcra; dorsal
fin long, occupying the posterior half of the back. Branchiostegals
numerous. Teeth tubercular or obtuse._

Extinct. From Carboniferous and Permian formations--_Eurynotus_,
_Benedenius_, _Mesolepis_, _Eurysomus_, _Wardichthys_, _Chirodus_
(M’Coy), _Platysomus_.

    [See Traquair, “On the Structure and Affinities of the Platysomidæ”, in
    “Trans. Roy. Soc.,” Edinb., vol. xxix.]

[Illustration: Fig. 147.--Platysomus gibbosus.]


                      EIGHTH SUB-ORDER--AMIOIDEI.

_Vertebral column more or less completely ossified, heterocercal.
Body covered with cycloid scales. Branchiostegals present._


                        FIRST FAMILY--CATURIDÆ.

_Notochord persistent, with partially ossified vertebræ; homocercal;
fins with fulcra. Teeth in a single series, small, pointed._

Extinct. _Caturus_ from the Oolite to the Chalk.

  [Illustration: Fig. 148.--Caturus furcatus (Solenhofen).]


                      SECOND FAMILY--LEPTOLEPIDÆ.

_Scales cycloid. Vertebræ ossified; homocercal; fins without fulcra;
dorsal short. Teeth minute, in bands, with canines in front._

Extinct, and leading to the living representative of this suborder.
_Thrissops_ with the dorsal fin placed far backwards, and opposite
to the long anal. _Leptolepis_ with the dorsal fin opposite to the
ventrals, from the Lias and Oolite. These fishes, as far as the
preserved parts are concerned, cannot be distinguished from Teleosteous
fishes, to which they are referred by some Palæontologists.

  [Illustration: Fig. 149.--Leptolepis sprattiformis.]


                         THIRD FAMILY--AMIIDÆ.

_Skeleton entirely ossified; a single large gular plate; homocercal;
fins without fulcra; a long soft dorsal fin. Abdominal and caudal parts
of the vertebral column subequal in extent. Branchiostegals numerous._

  [Illustration: Fig. 150.--Amia calva; _g_, gular plate.]

   AMIA.--Body rather elongate, sub-cylindrical, compressed behind.
   Snout short, cleft of the mouth of moderate width. Jaws with
   an outer series of closely-set pointed teeth, and with a band
   of rasp-like teeth; similar teeth on the vomer, palatine, and
   pterygoid bones. Anal short; caudal fin rounded. Gills four;
   air-bladder bifurcate in front, cellular, communicating with the
   pharynx.

The “Bow-fin” or “Mud-fish” (_A. calva_) is not uncommon in many
of the fresh waters of the United States; it grows to a length of two
feet. Little is known about its habits; small fish, crustaceans, and
aquatic insects, have been found in its stomach. Wilder has observed
its respiratory actions; it rises to the surface, and, without emitting
any air-bubble whatever, opens the jaws widely, and apparently gulps in
a large quantity of air; these acts of respiration are more frequently
performed when the water is foul or has not been changed; and there
is no doubt that an exchange of oxygen and carbonic acid is effected,
as in the lungs of aërial vertebrates. The flesh of this fish is not
esteemed.

Fossil remains occur in tertiary deposits of North America, for
instance in the Wyoming territory; they have been distinguished as
_Protamia_ and _Hypamia_.


                     SECOND SUB-CLASS--TELEOSTEI.

_Heart with a non-contractile bulbus arteriosus; intestine without
spiral valve; optic nerves decussating; skeleton ossified, with
completely formed vertebræ; vertebral column diphycercal or homocercal;
branchiæ free._[40]

The Teleostei form the majority of the fishes of the present fauna, and
are the geological successors of the Palæichthyes, undoubted Teleostei
not ranging farther back than the Chalk. This sub-class comprises an
infinite variety of forms; and as, naturally, many Ganoid fishes lived
under similar external conditions, and led a similar mode of life as
certain Teleostei, we find not a few analogous forms in both series:
some Ganoids resembling externally the Teleosteous Siluroids, others
the Clupeoids, others the Chætodonts, others the Scombresoces, etc.
But there is no direct genetic relation between those fishes, as some
Naturalists were inclined to believe.

The Teleostei are divided into six orders:--

   A. ACANTHOPTERYGII.--Part of the rays of the dorsal, anal, and
   ventral fins not articulated, spines. The lower pharyngeals
   separate. Air-bladder, if present, without pneumatic duct in the
   adult.

   B. ACANTHOPTERYGII PHARYNGOGNATHI.--Part of the rays of the
   dorsal, anal, and ventral fins not articulated, spines. The
   lower pharyngeals coalesced. Air-bladder without pneumatic duct.

   C. ANACANTHINI.--Vertical and ventral fins without spinous rays.
   Ventral fins, if present, jugular or thoracic. Air-bladder, if
   present, without pneumatic duct. Lower pharyngeals separate.

   D. PHYSOSTOMI.--All the fin rays articulated; only the first
   of the dorsal and pectoral fins is sometimes ossified. Ventral
   fins, if present, abdominal, without spine. Air-bladder, if
   present, with a pneumatic duct.

   E. LOPHOBRANCHII.--Gills not laminated, but composed of small
   rounded lobes, attached to the branchial arches. Gill-cover
   reduced to a large simple plate. A dermal skeleton replaces more
   or less soft integuments.

   F. PLECTOGNATHI.--A soft dorsal fin opposite to the anal;
   sometimes elements of a spinous dorsal. Ventral fins none,
   or reduced to spines. Gills pectinate; air-bladder without
   pneumatic duct. Skin with rough scutes, or with spines, or naked.


                     FIRST ORDER--ACANTHOPTERYGII.

_Part of the rays of the dorsal, anal, and ventral fins are not
articulated, more or less pungent spines. The lower pharyngeals are
generally separate. Air-bladder, if present, without pneumatic duct in
the adult._[41]


             FIRST DIVISION--ACANTHOPTERYGII PERCIFORMES.

_Body more or less compressed, elevated or oblong, but not elongate;
the vent is remote from the extremity of the tail, behind the ventral
fins if they are present. No prominent anal papilla. No superbranchial
organ. Dorsal fin or fins occupying the greater portion of the
back; spinous dorsal well developed, generally with stiff spines, of
moderate extent, rather longer than, or as long as, the soft; the soft
anal similar to the soft dorsal, of moderate extent or rather short.
Ventrals thoracic, with one spine and with four or five rays._


                        FIRST FAMILY--PERCIDÆ.

_The scales extend but rarely over the vertical fins, and the lateral
line is generally present, continuous from the head to the caudal fin.
All the teeth simple and conical; no barbels. No bony stay for the
præoperculum._

A large family, represented by numerous genera and species in fresh
waters, and on all the coasts of the temperate and tropical regions.
Carnivorous.

Fossil Percoids abound in some formations, for instance, at Monte
Bolca, where species of _Labrax_, _Lates_, _Smerdis_ and _Cyclopoma_
(both extinct), _Dules_, _Serranus_, _Apogon_, _Therapon_, and
_Pristipoma_ have been recognised. _Paraperca_ is a genus recently
discovered in the Marles of Aix-en-Provence. A species of _Perca_ is
known from the freshwater deposit of Oeningen.

   PERCA.--All the teeth are villiform, without canines; teeth
   on the palatine bones and vomer; tongue toothless. Two dorsal
   fins, the first with thirteen or fourteen spines; anal fin with
   two spines. Præoperculum and præorbital serrated. Scales small;
   head naked above. Branchiostegals seven. Vertebræ more than
   twenty-four.

The “Freshwater Perch” (_Perca fluviatilis_) is too familiarly known
to require description. It is generally distributed over Europe and
Northern Asia; and equally common in North America, there being no
sufficient ground for separating specifically the specimens of the
Western Hemisphere. It frequents especially still waters, and sometimes
descends into brackish water. Its weight does not seem to exceed 5
lbs. The female deposits her ova, united together by a viscid matter,
in lengthened or net-shaped bands, on waterplants. The number of
the eggs of one spawn may exceed a million. Two other species, _P.
gracilis_, from Canada, and _P. schrenckii_, from Turkestan, have been
distinguished, but they are very imperfectly known. An allied genus is
_Siniperca_, from Northern China.

  [Illustration: Fig. 151.--Perca fluviatilis, the Perch.]

   PERCICHTHYS.--Differing from _Perca_ especially in the number of
   the fin-spines, which are nine or ten in the first dorsal, and
   three in the anal fin. The upper surface of the head scaly.

These fishes represent the Freshwater Perches of the Northern
Hemisphere in the fresh waters of the temperate parts of South America.
Two species have been described from Patagonia, and one or two from
Chili and Peru.

   LABRAX.--All the teeth are villiform, without canines;
   teeth on the palatine bones, vomer, and the tongue. Two dorsal
   fins, the first with nine spines; anal fin generally with three.
   Præoperculum serrated, and with denticulations along its lower
   limb; præorbital with the margin entire. Scales rather small.
   Branchiostegals seven; well developed pseudobranchiæ.

The “Bass” are fishes common on the coasts of Europe and the Atlantic
coasts, and in the fresh waters of the United States and Canada. The
three European species are almost exclusively inhabitants of the sea,
entering brackish, but never fresh waters, whilst the American species,
the number of which is still uncertain, seem to affect principally
fresh water, although some are also found in the sea. The best known
European species is _Labrax lupus_ (see p. 41, Fig. 4), common on
the British coasts. It is a voracious fish, with a remarkably large
stomach, and received from the ancient Romans the appropriate name of
_lupus_. By the Greeks it was so highly esteemed that Archestratus
termed this or one of the two other closely-allied species, taken near
Milet, “offspring of the gods.” They attributed to it a tender regard
for its own safety; and Aristotle says that it is the most cunning of
fishes; and that, when surrounded by the net, it digs for itself a
channel of escape through the sand. Specimens of from two to three feet
are not scarce, but its flesh is nowadays much less esteemed than in
ancient times. Of the North American species _Labrax lineatus_ and
_Labrax rufus_ are the most common.

   LATES.--All the teeth are villiform, without canines; teeth on
   the palatine bones and vomer, but none on the tongue. Two dorsal
   fins--the first with seven or eight, the anal fin with two or
   three, spines. Præoperculum with strong spines at the angle and
   the lower limb; also the præorbital is strongly serrated. Scales
   of moderate size. Branchiostegals seven; pseudobranchiæ present.

Three well-known species belong to this genus. The Perch of the Nile
and other rivers of tropical Africa (_Lates niloticus_); the Perch of
the Ganges and other East Indian rivers, which enters freely brackish
water, and extends to the rivers of Queensland (_Lates calcarifer_).
These two species attain to a large size, the Indian species to a
length of five feet. Hamilton says that “the vulgar English in Calcutta
call it ‘Cockup,’ and that it is one of the lightest and most esteemed
foods brought to table in that city.” Specimens two feet in length and
caught in salt water are by far the best quality. The third species
(_Lates colonorum_) is found in Australia only, and does not appear to
grow to the same large size as its congeners.

Allied to _Lates_ is _Psammoperca_ from Australia.

   PERCALABRAX.--All the teeth villiform, without canines; teeth on
   the palatine bones and vomer, but none on the tongue. Two dorsal
   fins--the first with eleven, the anal fin with three spines.
   Præoperculum serrated along its hinder margin, and with strong
   spinous teeth below; præorbital not serrated. Scales rather
   small. Branchiostegals seven; pseudobranchiæ present.

This Perch (_Percalabrax japonicus_) is one of the most common fishes
on the coasts of China, Japan, and Formosa; the Japanese name it
“Zuzuki,” or “Seengo.”

   ACERINA.--All the teeth villiform, without canines; teeth on
   the vomer, but none on the palatine bones or the tongue. One
   continuous dorsal fin, of which the spinous portion consists of
   from thirteen to nineteen spines; two anal spines. Body rather
   low, with rather small scales. Bones of the skull with wide
   muciferous cavities; præoperculum denticulated.

Small freshwater perches, of which _A. cernua_, named “Pope” in
England, is the most common, and has the widest distribution in Central
Europe and Siberia. The two other species have a more restricted range,
_A. schrætzer_ being confined to the Danube and other rivers
emptying into the Black Sea; and _A. czekanowskii_ to Siberian
rivers. This genus is not represented in the Western Hemisphere.

   LUCIOPERCA.--Teeth in villiform bands, those in the jaws with
   additional canines; palatine bones toothed. Two dorsal fins--the
   first with from twelve to fourteen, the anal fin with two
   spines. Præoperculum serrated; scales small.

The “Pike-Perches” are inhabitants of many lakes and rivers of the
temperate northern zone. The European species is confined to the
eastern two-thirds of the continent, and one of the most esteemed
freshwater fishes; it attains to a length of three or four feet,
and to a weight of from 25 to 30 lbs. It has been recommended for
acclimatisation in England, and there is no doubt that in certain
localities it might prove a valuable addition to the native fauna; but
like all its congeners it is very voracious and destructive to smaller
fishes. Two other species inhabit rivers of European and Asiatic
Russia, and two or three the fresh waters of North America.

   PILEOMA.--All the teeth minute, villiform, without canines;
   teeth on the vomer and palatine bones. Two dorsal fins--the
   first with fourteen or fifteen spines. Body rather elongate,
   with small scales. Præoperculum not serrated.

Small freshwater perches abundant in the United States. Like the
following genus, and some others which need not be mentioned here,
they can be regarded as small, dwarfed representatives of the
preceding genera. The species seem to be numerous, but have not yet
been sufficiently well distinguished. The latest and best account of
them is by L. Vaillant, “Recherches sur les Poissons d’eaux douces de
l’Amérique septentrionale (_Etheostomatidæ_),” in Nouv. Archiv. du
Muséum d’Hist. Nat. de Paris, ix., 1873.

   BOLEOSOMA.--Allied to _Pileoma_, but with only nine or ten
   feeble spines in the first dorsal fin. North America.

   ASPRO.--Body elongate, cylindrical; snout thick, projecting
   beyond the mouth, which is situated at its lower side. All
   the teeth villiform, without canines; teeth on the vomer and
   palatine bones. Two separate dorsals. Præoperculum serrated;
   præorbital entire. Scales small.

Two small Perches from the Danube and some other rivers of the
continent of Europe, _Aspro vulgaris_ and _A. zingel_.

   CENTROPOMUS.--Body oblong, compressed, with scales of
   moderate size. All the teeth villiform, without canines; teeth
   on the vomer and palatine bones. Two dorsal fins, the first with
   eight strong spines, the anal with three, the second of which is
   very strong and long. Præoperculum with a double denticulated
   edge.

Numerous species are known from the West Indies and Central America.
These fishes are found in fresh, brackish, and salt water, and some of
the species indiscriminately enter all three kinds of water. They do
not grow to any large size, but are esteemed as food.

   ENOPLOSUS.--Body much elevated, the depth being still more
   increased by the high vertical fins. All the teeth are
   villiform, without canines; teeth on the vomer, palatine bones,
   and the tongue. Two dorsal fins, the first with seven spines.
   Præoperculum serrated, with spinous teeth at the angle. Scales
   of moderate size.

A small and very common marine species (_E. armatus_) on the coast
of Australia, especially New South Wales. It is readily recognised by
the peculiar shape of its body, and eight black transverse bands on a
whitish ground.

       *       *       *       *       *

This, and the preceding genus, leads to the true “Sea perches,” which
never, or but rarely, enter fresh water:--

   CENTROPRISTIS.--Body oblong, with scales of small or moderate
   size. Teeth villiform, with small canines in both jaws; vomerine
   teeth placed in an angular band, or a short triangular patch;
   teeth on the palatine bones, but none on the tongue. One dorsal,
   with the formula 10/12 or less; anal fin 3/7(6). Præoperculum
   serrated; sometimes with the angle projecting, and armed with
   long spines.

About twenty species of small size are known from temperate and
tropical seas.

ANTHIAS.--Body rather short, compressed, with scales of moderate
size. Teeth villiform, with small canines in both jaws; teeth on the
vomer, and palatine teeth. One dorsal, generally with ten spines; anal
fin with three; caudal forked. The rays of one or more fins may be
prolonged. Præoperculum serrated.

About twenty species are known from temperate and tropical seas; they
are mostly of small size, and agreeably coloured, pink and yellow
being the predominant colours. _Anthias sacer_ is common in the
Mediterranean, and was well known to the ancients. Aristotle says that
the fishers of Sponges call it sacred, because no voracious fishes came
to the places which it frequented, and the diver might descend with
safety.--_Callanthias_ is a genus closely allied to _Anthias_.

   SERRANUS.--Body oblong, compressed, with small scales. Teeth
   villiform, with very distinct canines in both jaws; teeth on the
   vomer and palatine bones, none on the tongue. One dorsal, mostly
   with nine or eleven, rarely with eight, ten or twelve spines;
   anal fin with three: all the spines being stout. Præoperculum
   serrated behind and at the angle, but not below.

  [Illustration: Fig. 152.--Serranus altivelis.]

The “Sea perches proper” are found on the shores of all temperate and
tropical seas, most abundantly in the latter. A few species enter
brackish and even fresh water, one having been found as high up the
Ganges as the confines of Nepal. However, all spawn in the sea. The
variety of species is almost infinite, about 150 being tolerably
well known, and many more having been described. The distinction of
the species is most difficult, and nearly impossible to those who
have no opportunity of closely and long observing them in nature,
as they are not only subject to great variation of colour, but also
to considerable changes dependent on age. Many are most agreeably
coloured, and ornamented with spots, or cross bands or longitudinal
stripes; colours which become more uniform with age in those species
which attain to a large size. The majority remain of rather small
size, growing to a length of one or two feet; but not a few reach
more than twice that length, and may even become dangerous to man.
Instances of bathers having been attacked by a gigantic species not
uncommon at the Seychelles and Aden are on record, the persons having
died from the injuries received. Almost all the species are eatable,
and many are esteemed as food. One species is common on the British
coasts (_S. cabrilla_), and probably some of the more southern species
(_S. scriba_ and _S. gigas_) occasionally wander as far northwards as
the British Channel. The species figured, _S. altvelis_, is locally
distributed over nearly all the tropical parts of the Indian Ocean, and
distinguished by particularly high dorsal and anal fins. _Anyperodon_
and _Prionodes_ are two genera closely allied to _Serranus_.

   PLECTROPOMA.--Form of the body and dentition (see p. 127, Fig.
   54) similar to that of _Serranus_, with a præoperculum serrated
   behind, and armed with spinous teeth below, which are directed
   forwards. Dorsal fin with from seven to thirteen spines.

About thirty species from tropical seas are known. _Trachypoma_ is
allied to this genus.

   POLYPRION.--Body oblong, rather compressed, covered with small
   scales. All the teeth are villiform; teeth on the vomer,
   palatine bones, and the tongue. One dorsal with eleven or twelve
   spines; anal with three. Præoperculum denticulated; a strong,
   rough, longitudinal ridge on the operculum.

Two species are known: one from the European coasts (_P. cernium_),
and one from Juan Fernandez (_P. kneri_). They attain to a weight of
80 lbs. and more. The European species has the habit of accompanying
floating wood, to which they are attracted by the small marine species
generally surrounding such objects, and affording a supply of food. It
is known by the name of “Stone-bass,” and excellent eating.

   GRAMMISTES.--Body rather short, compressed, covered with minute
   scales imbedded in the thick skin. All the teeth are villiform;
   teeth on the vomer and palatine bones. Two dorsal fins, the
   first with seven spines. Præoperculum without serrature, but
   with three short spines. A short skinny barbel is frequently
   developed at the chin.

Three species are known from the Indo-Pacific; they are of small
size. One, _G. orientalis_, is black, with six or seven white
longitudinal stripes, and one of the most common coast-fishes of that
ocean.

   RHYPTICUS.--Body oblong, compressed, covered with minute scales
   imbedded in the thick skin. All the teeth are villiform; teeth
   on the vomer and palatine bones. The spines of the vertical fins
   are but little developed, always in small number and short, and
   may disappear entirely. Præoperculum not serrated, with some
   obtuse spines.

Four species are known: three from the West Indies and one from the
Galapagoes Islands.

Other genera allied to the two preceding are _Aulacocephalus_ from
Mauritius, Reunion, and Japan; and _Myriodon_ from the coasts of
Australia.

   DIPLOPRION.--Body rather elevated, compressed, with small
   scales. All the teeth villiform; teeth on the vomer and palatine
   bones. Two dorsal fins, the first with eight spines; anal with
   two. Præoperculum with a double denticulated limb.

  [Illustration: Fig. 153.--Mesoprion monostigma.]

The single species known (_D. bifasciatum_), is very common in the East
Indian Archipelago, and on the coasts of Southern China and Japan. It
is of small size, and ornamented with two broad black cross-bands.

   MESOPRION.--Body oblong, compressed, covered with scales of
   moderate size. Teeth villiform, with canines in both jaws;
   teeth on the vomer and palatine bones. One dorsal fin, with
   ten or eleven, rarely with more spines; anal fin with three.
   Præoperculum serrated; in some species (_Genyoroge_) a more or
   less distinct spinous knob projects from the surface of the
   interoperculum, and is received in a more or less deep notch of
   the præopercular margin.

  [Illustration: Fig. 154.--Opercles _a_, of _Mesoprion_;
  _b_, of _Genyoroge_; _o_, knob received in a notch
  of the præoperculum.]

About seventy species are known from tropical seas in both hemispheres,
but it is noteworthy that the species with the peculiar protuberance
of the interoperculum are confined to the Indo-Pacific. The coloration
is much more simple than in the small-scaled Serrani, a uniform hue
of greenish, pink, or red prevailing; species with longitudinal bands
are scarce, but not rarely dark cross-bands or a large spot on the
side occur. The majority of the species remain within very moderate
dimensions, specimens exceeding three feet in length being scarce. They
are generally eaten, and some of the species belong to the commonest
fishes of the tropics, as _M. bengalensis_, _chrysurus_, _gembra_,
_griseus_, and others.

_Glaucosoma_ from Japan and Australia is allied to _Mesoprion_.

   DULES.--Body oblong, compressed, with scales of moderate size,
   and very indistinctly ctenoid. All the teeth are villiform;
   teeth on the vomer and palatine bones. One dorsal with ten
   spines; anal fin with three. Præoperculum serrated. Six
   branchiostegals only.

About ten species are known, inhabiting fresh waters of the coasts of
the Indo-Pacific, and being especially common in the islands of this
region, and also in Tropical Australia. Some live also in brackish
water. Though of small size they are esteemed as food.

   THERAPON.--Body oblong, compressed, with scales of moderate
   size. All the teeth are villiform, those of the vomer and
   palatine bones being rudimentary, and frequently absent. One
   dorsal, with a depression in its upper margin, and twelve or
   thirteen spines; anal fin with three. Præoperculum serrated.
   Air-bladder with two divisions, an anterior and posterior. Six
   branchiostegals.

About twenty species are known, the distribution of which nearly
coincides with _Dules_, but as some of the species are more or less
marine, the genus is spread over the whole area of the tropical
Indo-Pacific. Other species, especially those of Australian rivers,
are entirely limited to fresh water. _Th. theraps_, _Th. servus_, and
_Th. cuvieri_ belong to the most common fishes of that area, extending
from the east coast of Africa to Polynesia. They are readily recognised
by the blackish longitudinal bands with which the body is ornamented.
All the species are of small size. _Helotes_ is closely allied to this
genus.

   PRISTIPOMA.--Body oblong, compressed, with ctenoid scales of
   moderate size. Cleft of the mouth horizontal, not very wide,
   with the jaws nearly equal in length anteriorly; a central pit
   below the chin; villiform teeth in the jaws without canines;
   palate toothless. One dorsal, with eleven to fourteen spines;
   anal with three. Vertical fins not scaly, or with scales along
   the base only. Præoperculum serrated. Branchiostegals, seven.

  [Illustration: Fig. 155.--Lower view of mandible of Pristipoma
  manadense.]

About forty species are known, all from the sea. They are extremely
common between the tropics, some of the species extending into the
neighbouring sub-tropical parts. They do not attain a large size, and
generally have a plain coloration. _Conodon_ is an allied genus.

  [Illustration: Fig. 156.--Hæmulon brevirostrum.]

   HÆMULON.--Body oblong, compressed, with ctenoid scales of
   moderate size. Cleft of the mouth horizontal, generally wide,
   with the jaws equal in length anteriorly; a central pit below
   the chin; villiform teeth in the jaws, without canines; palate
   toothless. One dorsal, with twelve or thirteen spines; anal with
   three; the soft portions of the vertical fins scaly to their
   margins. Præoperculum serrated. Branchiostegals, seven.

Marine; sixteen species are known from the coasts of Tropical America;
they are of rather small size. The species figured occurs on both sides
of Central America. _Hapalogenys_ is an allied genus.

   DIAGRAMMA.--Body oblong, compressed, covered with rather small
   ctenoid scales. Upper profile of the head parabolic; cleft of
   the mouth small, horizontal; from four to six pores under the
   mandible, but without central pit. Teeth villiform, without
   canines; palate toothless. One dorsal fin, with from nine to
   fourteen spines; anal with three. Vertical fins not scaly.
   Præoperculum serrated; infraorbital not armed. Branchiostegals,
   six or seven.

  [Illustration: Fig. 157.--Diagramma orientale, from the
  Indo-Pacific.]

Forty species are known, which, with very few exceptions, belong to
the tropical parts of the Indo-Pacific. Some attain to a size not very
common among Sea-Perches, viz. to a length of from three to four feet.
Many are agreeably coloured with black bands or spots. All appear to be
esteemed as food. _Hyperoglyphe_ from Australia is allied to this
genus.

   LOBOTES.--Body rather elevated, compressed, with ctenoid scales
   of moderate size. Eye rather small. Snout obtuse, with oblique
   cleft of the mouth, and with the lower jaw longest. Teeth
   villiform, without canines; palate toothless. One dorsal fin
   with twelve spines; anal with three. Præoperculum denticulated.
   Branchiostegals, six.

A remarkable fish (_L. auctorum_) on account of its extraordinary
range. Common in many localities, scarcer in others, it occurs in the
East Indies, and on all the Atlantic coasts of tropical and temperate
America. Döderlein found it on the coast of Sicily in 1875. It lives in
salt and brackish water, and is known to attain to a length of two feet.

   HISTIOPTERUS.--Body rather elevated, strongly compressed, with
   very small scales. Snout much produced, the anterior profile of
   the head being concave. Mouth small, at the end of the snout.
   Teeth villiform, without canines; palate toothless. Some of the
   spines and rays of the vertical and pectoral fins very long. One
   dorsal, with about ten spines; anal with three. Præopercular
   margin partly serrated. Branchiostegals, six.

Marine. Four species are known from Japan and South Australia. The
species figured attains to a length of 20 inches, and is esteemed as
food. It is known at Melbourne by the names of “Boar Fish” or “Bastard
Dorey.”

  [Illustration: Fig. 158.--Histiopterus recurvirostris.]

   GERRES.--Body oblong, or rather elevated, covered with scales
   of moderate size, which are either entirely smooth or minutely
   ciliated. Mouth very protractile, and descending when thrust
   out. Eye rather large. No canine teeth; dentition feeble, and
   palate toothless. The two divisions of the dorsal fin are nearly
   separated by a deep incision. Formula of the vertical fins--D.
   9/10 A. 2·3/7·9. Caudal fin forked. Præoperculum generally
   without denticulation. Lower pharyngeal bones coalescent.

  [Illustration: Fig. 159.--Gerres altispinis, from the mouth of
  the Ganges.]

More than thirty species are known of this genus, which bear so close a
resemblance to one another that their distinction is rather difficult.
They live in the seas between the Tropics, and some, perhaps all, of
the species enter fresh water. Very rarely they exceed a length of ten
inches; nearly all have a plain silvery coloration. The coalescence
of their lower pharyngeals renders their systematic position rather
uncertain, and, indeed, some Ichthyologists have referred them to the
Pharyngognaths.

   SCOLOPSIS.--Body oblong, covered with scales finely serrated
   and of moderate size. Jaws nearly equal in length anteriorly;
   cleft of the mouth horizontal. Teeth villiform, without canines;
   palate toothless. One dorsal fin. Formula of the vertical fins:
   D. 10/9 A. 3/7. Caudal fin forked. Præoperculum distinctly
   denticulated; infraorbital ring with a spine directed backwards.
   Branchiostegals, five.

  [Illustration: Fig. 160.--Infraorbital spine of Scolopsis
  monogramma.]

Marine, and of small size. Twenty-five species are known from the
tropical parts of the Indo-Pacific. _Heterognathodon_ is an allied
genus, but without the infraorbital spine.

   DENTEX.--Body oblong, covered with ctenoid scales of
   moderate size. Cleft of the mouth nearly horizontal, with the
   jaws equal in length anteriorly. Canine teeth in both jaws;
   palate toothless. One dorsal fin. Formula of the vertical fins:
   D. 10·13/10·12 A. 3/8·9. Caudal fin forked. Præoperculum without
   serrature; præorbital unarmed and broad, there being a wide
   space between the eye and the cleft of the mouth. Cheek covered
   by more than three series of scales. Branchiostegals, six.

Marine Fishes, rather locally distributed in the Mediterranean, on the
south coast of Africa, in the Red Sea, East Indian Archipelago, and
on the coasts of China and Japan. About fourteen species are known,
some of which attain a weight of 30 lbs. and more. They form a not
unimportant article of food where they are found in any number, as on
the Cape of Good Hope. The species found in the Mediterranean (_D.
vulgaris_) wanders sometimes to the south coast of England, and is
one of the larger species. The coloration of these fishes is rather
uniform, silvery, or pink, or greenish. _Symphorus_ is an allied genus
from the Indo-Pacific.

   SYNAGRIS.--Body rather elongate, covered with ciliated
   scales of moderate size. Cleft of the mouth horizontal, with
   the jaws equal in length anteriorly. One continuous dorsal,
   with feeble spines; dorsal 10/9, anal 3/7. Caudal deeply
   forked. Teeth villiform, with canines at least in the upper
   jaw. Infraorbital not armed; præoperculum without, or with a
   very indistinct serrature. Cheek with three series of scales.
   Branchiostegals six.

Marine fishes of small size; about twenty species are known from the
tropical parts of the Indo-Pacific. _Pentapus_, _Chætopterus_, and
_Aphareus_ are allied genera from the same area.

   MAENA.--Body oblong, compressed, covered with ciliated scales
   of moderate size. Mouth very protractile, the intermaxillary
   pedicles extending backwards to the occiput. Teeth villiform;
   minute teeth on the vomer. One dorsal, scaleless, with feeble
   spines. D. 11/11, A. 3/9. Caudal fin forked. Præoperculum
   without serrature. Branchiostegals six.

Small fishes from the Mediterranean, known to the ancients; valueless
as food. Three species.

   SMARIS.--Body oblong or cylindrical, covered with rather small
   ciliated scales. Mouth very protractile, the intermaxillary
   pedicles extending backwards to the occiput. Teeth villiform.
   Palate toothless. One dorsal, scaleless, with eleven or more
   very feeble spines; anal with three. Caudal fin forked.
   Præoperculum without serrature. Branchiostegals six.

Small fishes from the Mediterranean. Six species.

   CÆSIO.--Body oblong, covered with ciliated scales of moderate
   size. Cleft of the mouth more or less oblique, with the
   jaws equal in length anteriorly, or with the lower somewhat
   projecting. Teeth villiform; palate generally toothless. One
   dorsal, with from nine to thirteen very feeble spines, with the
   anterior part highest, and the posterior covered with minute
   scales. Caudal fin deeply forked. Præoperculum without, or with
   minute, serrature.

Small fishes from the Indo-Pacific. Twelve species.

   ERYTHRICHTHYS.--Body elongate, covered with small ciliated
   scales. Mouth very protractile, the pedicles of the
   intermaxillary extending to the occiput. Dentition quite
   rudimentary or entirely absent Two dorsal fins connected by
   a series of very feeble spines; also the anterior spines are
   feeble. Præoperculum not serrated.

  [Illustration: Fig. 161.--Erythrichthys nitidus.]

  [Illustration: Fig. 162.--Enlarged scale.]

  [Illustration: Fig. 163.--Protractile mouth.]

Small fishes from various tropical and temperate seas. Four species:
the species figured occurs, but is not common, on the coasts of
Western Austria, Tasmania, and New Zealand.

   OLIGORUS.--Body oblong, covered with small scales. Cleft of the
   mouth rather oblique, the lower jaw being the longer. Teeth
   villiform, without canines; teeth on the vomer and palatine
   bones. One dorsal, with eleven spines; anal with three; caudal
   fin rounded. Præoperculum with a single smooth or obtusely
   denticulated margin.

To this genus belong two fishes well known on account of the excellent
flavour of their flesh. The first (_O. macquariensis_) is called
by the colonists “Murray-Cod,” being plentiful in the Murray River
and other rivers of South Australia. It attains to a length of more
than three feet, and to a weight of nearly 100 lbs. The second (_O.
gigas_) is found in the sea, on the coast of New Zealand, and called
by the Maoris and colonists “Hapuku.” Its average weight is about 45
lbs., but occasionally large specimens of more than a hundredweight
are caught. At certain localities it is so plentiful that it may form
an important article of trade. Dr. Hector, who has had opportunity of
examining it in a fresh state, has pointed out anatomical differences
from the Murray-Cod, from which it appears that it would be better
placed in a distinct genus.

  [Illustration: Fig. 164.--The Murray-Cod, _Oligorus
  macquariensis_.]

   GRYSTES.--Body oblong, covered with scales of moderate size. All
   the teeth villiform, without canines; teeth on the vomer and
   palatine bones. One dorsal fin with ten spines; anal with three;
   caudal fin rounded. Præoperculum with a single smooth margin.

One species, from the fresh waters of the United States (_G.
salmonoides_), attains to a length of more than two feet. It is
known by the name of “Growler,” and eaten.

   ARRIPIS.--Body oblong, covered with scales of moderate size. All
   the teeth villiform, without canines; teeth on the vomer and
   palatine bones. One dorsal fin, with nine slender spines; anal
   with three. Præoperculum denticulated.

  [Illustration: Fig. 165.--_Arripis salar_, South Australia.]

Three species are known, from the coasts of Southern Australia and New
Zealand. They are named by the colonists Salmon or Trout, from their
elegant form and lively habits, and from the sport they afford to the
angler. Their usual size is from 1 to 3 lbs., but specimens of double
that weight are taken. The smaller specimens are the more delicate and
better flavoured. When not fresh, they are liable to assume poisonous
properties; and cases of poisoning are not unfrequently caused by them.

   HURO.--Body oblong, compressed, covered with scales of moderate
   size. All the teeth villiform; bones of the head without
   serrature. Mouth rather oblique, with the lower jaw projecting.
   Two dorsal fins, the first with six spines.

The “Black Bass” of Lake Huron (_Huro nigricans_).

   AMBASSIS.--Body short, strongly compressed, covered with large
   thin deciduous scales. Mouth oblique, with the lower jaw
   longest; teeth villiform, without conspicuously larger canines;
   teeth on the vomer and palatine bones. Two dorsal fins, the
   first with seven, the anal with three spines; a horizontal
   spine pointing forwards in front of the dorsal fin. The lower
   limb of the præoperculum with a double serrated margin.

This genus comprises the smallest of all Percoids, some of the species
not much exceeding one inch in length. They are most abundant on the
coasts of the tropical Indo-Pacific, and in the fresh waters belonging
to that area. The species are numerous (some thirty having been
described), and very difficult to distinguish. Their coloration is very
plain, a silvery hue prevailing over the whole fish.

   APOGON.--Body rather short, covered with large deciduous scales.
   Mouth oblique, with the lower jaw longest; teeth villiform,
   without canines; teeth on the vomer and palatine bones. Two
   dorsal fins, the first with six or seven, the anal with two
   spines. Præoperculum with a double edge on the margin, one or
   both edges being serrated. Seven branchiostegals.

  [Illustration: Fig. 166.--Apogon frenatus.]

Although of similarly small size, the fishes of this genus represent a
more highly developed form of the Percoid type than _Ambassis_. Their
distribution coincides very much with that of _Ambassis_, but they
are chiefly marine, comparatively few of the species entering fresh
water. They belong to the kind of fishes which, from their habit,
are termed “Coral Fishes,” being found in greatest abundance on, or
in the neighbourhood of, coral reefs, in company with Chætodonts,
Pomacentridæ, and others. Their colours also are ornamental and highly
diversified, as is generally the case in coral fishes, the majority of
the species showing transverse or longitudinal bands or large spots,
and numerous other smaller markings which, in the dead fish, soon
disappear. Nearly one hundred species have been described, of which
a few only occur in the Atlantic, one extending northwards into the
Mediterranean.

_Chilodipterus_, _Acropoma_, and _Scombrops_ are allied genera, but
with canine teeth in one or both jaws.

   POMATOMUS.--Body oblong, covered with scales of moderate size.
   Eye very large. All the teeth villiform, without canines; teeth
   on the vomer and palatine bones. Two dorsal fins, the first with
   seven, the anal with two spines. No serration on any of the
   bones of the head. Branchiostegals seven.

One species only is known, _P. telescopium_, which grows to a length
of nearly two feet. It is not uncommon in the Mediterranean and
neighbouring parts of the Atlantic, but only occasionally caught, as it
lives habitually at a greater depth than any other Percoid as far as is
known at present, probably at depths from 80 to 200 fathoms; a habit
sufficiently indicated by its exceedingly large eye.

PRIACANTHUS.--Body short, compressed, covered with small rough
scales, which extend also over the short snout. Lower jaw and chin
prominent. Eye large. All the teeth villiform, without canines; teeth
on the vomer and palatine bones. One dorsal fin with ten spines, anal
with three. Præoperculum serrated, with a more or less prominent, flat,
triangular spine at the angle.

A very natural genus, easily recognised, and without direct relation to
the other Percoid genera. The species, of which seventeen are known,
are spread over nearly all the tropical seas, and belong to the more
common fishes. They scarcely exceed a length of twelve inches, and are
very uniformly coloured, red, pink, and silvery prevailing.

       *       *       *       *       *

The following three genera form a group by themselves, which, however,
is defined rather by its geographical limits and similarity of general
appearance than by distinctive anatomical characters. The species are
abundant in the fresh waters of the United States, and well known by
the name of “Sun Fishes.” They rarely exceed a length of six inches,
and are not used as food. The number of species is uncertain.

   CENTRARCHUS.--Body short, compressed, with scales of moderate
   size. All the teeth villiform, without canines; teeth on the
   vomer, palatines, and on the tongue. One dorsal fin; anal
   generally with more than three spines. Præoperculum without
   serrature; operculum not lobed.

   BRYTTUS.--Body short, compressed, with scales of moderate size.
   All the teeth villiform, without canines; teeth on the vomer and
   palatine bones. One dorsal fin with nine or ten, anal with three
   spines. Præoperculum not serrated; operculum with a rounded
   membranaceous coloured lobe behind.

   POMOTIS.--Body short, compressed, with scales of moderate
   length. All the teeth villiform, without canines; teeth on the
   vomer, but none on the palatine bones. One dorsal, with from
   nine to eleven spines, anal with three. Præoperculum entire
   or minutely serrated; operculum with a rounded membranaceous
   coloured lobe behind.

       *       *       *       *       *

A NORTH AMERICAN Freshwater genus, _Aphredoderus_, occupies a perfectly
isolated position in the system, and is evidently the type of a
distinct family. It resembles the “Sun-fishes” of the same country with
regard to the structure of the vertical fins, but has the vent situated
in front of the ventrals, which are composed of more than five soft
rays. The body is oblong, compressed, covered with ctenoid scales. The
dorsal fin is single, and has three spines in front. Infraorbital and
præoperculum with spinous teeth. Villiform teeth in the jaws, on the
vomer and palatine bones. _A. sayanus_ from the southern streams and
fresh waters of the Atlantic States.

To complete the list of Percoid genera, we have to mention the
following:--_Siniperca_, _Etelis_, _Niphon_, _Aprion_, _Apsilus_,
_Pentaceros_, _Velifer_, _Datnioides_, _Percilia_, _Lanioperca_.


                     SECOND FAMILY--SQUAMIPINNES.

_Body compressed and elevated, covered with scales, either finely
ctenoid or smooth. Lateral line continuous, not continued over the
caudal fin. Mouth in front of the snout, generally small, with lateral
cleft. Eye lateral, of moderate size. Six or seven branchiostegals.
Teeth villiform or setiform, in bands, without canines or incisors.
Dorsal fin consisting of a spinous and soft portion of nearly equal
development; anal with three or four spines, similarly developed as
the soft dorsal, both being many-rayed. The vertical fins more or less
densely covered with small scales. The lower rays of the pectoral fin
branched, not enlarged; ventrals thoracic, with one spine and five soft
rays. Stomach coecal._

The typical forms of this family are readily recognised by the form
of their body, and by a peculiarity from which they derive their
name _Squamipinnes_; the soft, and frequently also the spinous part
of their dorsal and anal fins are so thickly covered with scales
that the boundary between fins and body is entirely obliterated. The
majority are inhabitants of the tropical seas, and abound chiefly
in the neighbourhood of coral-reefs. The beauty and singularity of
distribution of the colours of some of the genera, as _Chætodon_,
_Heniochus_, _Holacanthus_, is scarcely surpassed by any other group
of fishes. They remain within small dimensions, and comparatively few
are used as food. They are carnivorous, feeding on small invertebrates.
Only a few species enter brackish water.

Extinct representatives of this family are not scarce at Monte Bolca
and in other tertiary formations. All, at least those admitting of
definite determination, belong to existing genera, viz. _Holacanthus_,
_Pomacanthus_, _Ephippium_, _Scatophagus_. Very singular is the
occurrence of _Toxotes_ in the Monte Bolca strata.

The following genera have no teeth on the palate:--

   CHÆTODON.--One dorsal fin, without any notch in its upper
   margin, and with the soft and spinous portions similarly
   developed; none of the spines elongate. Snout short or of
   moderate length. Præoperculum without, or with a fine,
   serration, and without spine at the angle. Scales generally
   large or of moderate size.

  [Illustration: Fig. 167.--Chætodon ephippium.]

Seventy species are known from the tropical parts of the Atlantic and
Indo-Pacific, nearly all being beautifully ornamented with bands or
spots. Of the ornamental markings a dark or bicoloured band, passing
through the eye and ascending towards the back, is very generally
found in these fishes; it frequently occurs again in other marine
Acanthopterygians, in which it is not rarely a sign of the immature
condition of the individual. The Chætodonts are most numerous in the
neighbourhood of the coral-reefs of the Indo-Pacific, the species
figured (_C. ephippium_) being as common in the East Indian
Archipelago as in Polynesia, like many others of its congeners.

   CHELMO differs from _Chætodon_ only in having the snout produced
   into a more or less long tube.

  [Illustration: Fig. 168.--Chelmo marginalis, from the coast of
  Australia.]

Only four species are known, locally distributed in the tropical seas.
_Ch. rostratus_, the oldest species known, is said to have the instinct
of throwing a drop of water from its bill so as to light upon any
insect resting on a leaf, and thus make it fall, that it may instantly
dart upon it. This statement is erroneous, and probably rests upon
the mistaken notion that the long bill is especially adapted for this
manœuvre, which, indeed, is practised by another fish of this family
(_Toxotes_). The long slender bill of Chelmo (which is a true saltwater
fish) rather enables it to draw from holes and crevices animals which
otherwise could not be reached by it.

   HENIOCHUS.--One dorsal, with from eleven to thirteen spines, the
   fourth of which is more or less elongate and filiform. Snout
   rather short or of moderate length. Præoperculum without spine.
   Scales of moderate size.

Four species are known from the tropical Indo-Pacific. _H.
macrolepidotus_ is one of the most common fishes of that area; the
species figured (_H. varius_) retains in a conspicuous manner
horn-like protuberances on bones of the head, with which the young of
all the species of this genus seem to be armed.

  [Illustration: Fig. 169.--Heniochus varius.]

   HOLACANTHUS.--Præoperculum with a strong spine at the angle. One
   dorsal, with from twelve to fifteen spines. Scales of moderate
   or small size.

Forty species are known, which, in their geographical distribution
accompany, and are quite analogous to, the Chætodonts. One of the most
common and most beautiful is called “Emperor of Japan” by the Dutch,
which name has been adopted by Bloch for its specific designation,
_Holacanthus imperator_. Its body is blue, longitudinally traversed
by about thirty yellow bands; the ocular band, and the side behind the
head, are black, edged with yellow; the caudal fin is yellow. It is a
large species of this genus, sometimes attaining a length of 15 inches,
and as an article of food is one of the most esteemed of all the Indian
species. With regard to beauty of colours it is surpassed by another
allied species, _H. diacanthus_, which likewise ranges from the east
coast of Africa to Polynesia.

   POMACANTHUS differs from _Holacanthus_ in having from eight to
   ten spines only in the dorsal fin.

The single species (_P. paru_) on which this genus is founded is
one of the most common fishes of the West Indies, and offers one of
the most remarkable instances of variation of colour within the limits
of the same species: some specimens being ornamented with more or less
distinct yellowish cross-bands, others with yellow crescent-shaped
spots; in others black spots predominate.

  [Illustration: Fig. 170.--Scatophagus multifasciatus.]

   SCATOPHAGUS.--Two dorsal fins, united at the base, the first
   with ten or eleven spines; only the second is scaly. A recumbent
   spine before the dorsal, pointing forwards. Anal with four
   spines. Snout rather short. Præoperculum without spine. Scales
   very small.

Four species are known, from the Indian Ocean, of which _S. argus_
is the most generally known, in fact, one of the most common Indian
shore-fishes. It freely enters large rivers, and is said not to be
particular in the selection of its food. The species figured (_S.
multifasciatus_) represents _S. argus_ on the coasts of Australia.

  [Illustration: Fig. 171.--Bony enlargement of cranial bones of
  Ephippus. _a_, Enlargement of the frontal, and _b_,
  of the supraoccipital bones; _c_, interorbital septum;
  _d_, basis cranii. ⅓ nat. size.]

   EPHIPPUS.--Snout short, with the upper profile parabolic. Dorsal
   fin deeply emarginate between the spinous and soft portions,
   the former with nine spines, the third of which is rather
   elongate, and flexible; spinous portion not scaly; anal spines
   three. Pectoral fin short. Præoperculum without spine. Scales of
   moderate size, or rather small.

Two or three species are known from the warmer parts of the Atlantic
and Indian Oceans. The Atlantic species (_E. faber_) shows the
remarkable peculiarity that in old specimens (12 and more inches long)
the occipital crest, and sometimes some of the anterior neural and
hæmal spines are enormously enlarged into a globular bony mass. This
can hardly be regarded as a pathological change of the bone, as it has
been found in all old specimens, without exception.

_Drepane_ is allied to _Ephippus_, but has very long falciform pectoral
fins. The single species _D. punctata_ is common in the Indian Ocean
and on the coasts of Australia. _Hypsinotus_, from Japan, appears to
inhabit a greater depth than the other Squamipinnes.

_Scorpis_ and _Atypichthys_ are genera distinguished from the
preceding by the presence of vomerine teeth. They belong to the
coast-fauna of Australia, New Zealand, and Chili.

   TOXOTES.--Body short, compressed, covered with scales of
   moderate size. Snout pointed, with a wide lateral mouth and
   projecting lower jaw. One dorsal, with five strong spines
   situated on the posterior part of the back; the soft portion
   and the anal fin scaly, the latter with three spines. Villiform
   teeth in the jaws, on the vomer and palatine bones. Scales of
   moderate size, cycloid.

  [Illustration: Fig. 172.--Toxotes jaculator.]

Two species are known from the East Indies, one (_T. jaculator_),
which is the more common, ranging to the north coast of Australia. It
has received its name from its habit of throwing a drop of water at an
insect which it perceives close to the surface, in order to make it
fall into it. The Malays, who call it “Ikan sumpit,” keep it in a bowl,
in order to witness this singular habit, which it continues even in
captivity.


                        THIRD FAMILY--MULLIDÆ.

_Body rather low and slightly compressed, covered with large thin
scales, without or with an extremely fine serrature. Two long erectile
barbels are suspended from the hyoid, and are received between the rami
of the lower jaw and opercles. Lateral line continuous. Mouth in front
of the snout, with the cleft lateral and rather short; teeth very
feeble. Eye lateral, of moderate size. Two short dorsal fins remote
from each other, the first with feeble spines; anal similar to the
second dorsal. Ventrals with one spine and five rays. Pectorals short.
Branchiostegals four; stomach siphonal._

The “Red Mullets” form a very natural family, which, on account of
slight modifications of the dentition, has been divided into several
sub-genera--_Upeneoides_, _Upeneichthys_, _Mullus_, _Mulloides_, and
_Upeneus_. They are marine fishes, but many species enter brackish
water to feed on the animalcules abounding in the flora of brack-water.
About forty different species are known chiefly from tropical seas,
the European species (_M. barbatus_, see p. 43, Fig. 7), extending
far northwards into the temperate zone. None attain to a large size,
specimens of from two to three lbs. being not common, but all are
highly esteemed as food.

The most celebrated is the European species (of which there is one
only, _M. surmuletus_ being probably the female). The ancient Romans
called it _Mullus_, the Greeks τριγλη. The Romans priced it above any
other fish; they sought for large specimens far and wide, and paid
ruinous prices for them.

              “Mullus tibi quatuor emptus
    Librarum, cœnæ pompa caputque fuit,
    Exclamare libet, non est hic improbe, non est
    Piscis: homo est; hominem, Calliodore, voras.”
                                     MARTIAL, x. 31.

Then, as nowadays, it was considered essential for the enjoyment of
this delicacy that the fish should exhibit the red colour of its
integuments. The Romans brought it, for that purpose, living into the
banqueting room, and allowed it to die in the hands of the guests, the
red colour appearing in all its brilliancy during the death struggle of
the fish. The fishermen of our times attain the same object by scaling
the fish immediately after its capture, thus causing a permanent
contraction of the chromatophors containing the red pigment (see p.
183).


                        FOURTH FAMILY--SPARIDÆ.

_Body compressed, oblong, covered with scales, the serrature of which
is very minute, and sometimes altogether absent. Mouth in front of the
snout, with the cleft lateral. Eye lateral, of moderate size. Either
cutting teeth in front of the jaws, or molar teeth on the side; palate
generally toothless. One dorsal fin, formed by a spinous and soft
portion of nearly equal development. Anal fin with three spines. The
lower rays of the pectoral fin are generally branched, but in one genus
simple. Ventrals thoracic, with one spine and five rays._

The “Sea-breams” are recognised chiefly by their dentition, which is
more specialised than in the preceding families, and by which the
groups, into which this family has been divided, are characterised.
They are inhabitants of the shores of all the tropical and temperate
seas. Their coloration is very plain. They do not attain to a large
size, but the majority are used as food.

The extinct forms found hitherto are rather numerous; the oldest come
from the cretaceous formation of Mount Lebanon; some belong to living
genera, as _Sargus_, _Pagellus_; of others from Eocene and Miocene
formations no living representative is known--_Sparnodus_, _Sargodon_,
_Capitodus_, _Soricidens_, _Asima_.

_First Group--Cantharina._--More or less broad cutting, sometimes
lobate, teeth in front of the jaws; no molars or vomerine teeth;
the lower pectoral rays are branched. Partly herbivorous, partly
carnivorous. The genera belonging to this group are:--_Cantharus_
from the European and South African coasts, of which one species (_C.
lineatus_), is common on the coasts of Great Britain, and locally known
by the names “Old Wife,” “Black Sea-bream;” _Box_, _Scatharus_, and
_Oblata_ from the Mediterranean and neighbouring parts of the Atlantic;
_Crenidens_ and _Tripterodon_ from the Indian Ocean; _Pachymetopon_,
_Dipterodon_, and _Gymnocrotaphus_ from the Cape of Good Hope;
_Girella_ and _Tephræops_ from Chinese, Japanese, and Australian Seas;
_Doydixodon_ from the Galapagos Islands and the coasts of Peru.

  [Illustration: Fig. 173.--Tephræops richardsonii, from King
  George’s Sound.]

_Second Group--Haplodactylina._--In both jaws flat and generally
tricuspid teeth; no molars; vomerine teeth. The lower pectoral rays
simple, not branched. Vegetable feeders. Only one genus is known,
_Haplodactylus_, from the temperate zone of the Southern Pacific.

_Third Group--Sargina._--Jaws with a single series of incisors
in front, and with several series of rounded molars on the side. One
genus is known, _Sargus_, which comprises twenty species; several
of them occur in the Mediterranean and the neighbouring parts of the
Atlantic, and are popularly called “Sargo,” “Sar,” “Saragu:” names
derived from the word Sargus, by which name these fishes were well
known to the ancient Greeks and Romans. One of the largest species is
the “Sheep’s-head” (_Sargus ovis_), from the coasts of the United
States, which attains to a weight of 15 lbs., and is highly esteemed on
account of the excellency of its flesh. Singularly enough, this genus
occurs also on the east coast of Africa, one of these East-African
species being identical with _S. noct_ from the Mediterranean.
These fishes evidently feed on hard-shelled animals, which they crush
with their molar teeth.

  [Illustration: Fig. 174.--The Sheep’s-head, _Sargus ovis_,
  of North America.]

  [Illustration: Fig. 175.--Scale of Lethrinus.]

_Fourth Group--Pagrina._--Jaws with conical teeth in front and molar
teeth on the sides. Feeding, as the preceding, on hard-shelled animals,
like Mollusks and Crustaceans. This group is composed of several
genera:--

   LETHRINUS.--Cheeks scaleless. Body oblong, covered with scales
   of moderate size (L. lat. 45–50). Canine teeth in front; lateral
   teeth in a single series, broadly conical or molar-like. Formula
   of the fins: D. 10/9, A. 3/8.

More than twenty species are known, all of which, with one exception,
occur in the tropical Indo-Pacific. The species, forming this
exception, occurs, singularly enough, on the west coast of Africa,
where more than one Indian genus reappears in isolated representative
species. Some Lethrini attain to a length of three feet.

_Sphærodon_ is closely allied to _Lethrinus_, but has scales on the
cheek. One species from the Indo-Pacific.

   PAGRUS.--Body oblong, compressed, with scales of moderate size.
   Several pairs of strong canine-like teeth in both jaws; molars
   arranged in two series. Cheeks scaly. The spines of the dorsal
   fin, eleven or twelve in number, are sometimes elongate, and can
   be received in a groove; anal spines three.

Thirteen species are known, chiefly distributed in the warmer parts
of the temperate zones, and more scantily represented between the
tropics. Several species (_P. vulgaris, P. auriga, P. bocagii_) occur
in the Mediterranean and the neighbouring parts of the Atlantic; one
(_P. argyrops_) is well known on the coasts of the United States
under the names of “Scup,” “Porgy,” or “Mishcup,” and one of the most
important food fishes, growing to a length of 18 inches and a weight
of 4 lbs.; another (_P. unicolor_) is one of the best-known sea-fishes
of Southern Australia and New Zealand, where it is called “Snapper;”
it is considered very good eating, like all the other species of this
genus, and attains, like some of them, a length of more than 3 feet and
a weight exceeding 20 lbs.

   PAGELLUS.--Body oblong, compressed, with scales of moderate
   size. Jaws without canines; molars on the sides arranged in
   several series. Cheeks scaly. The spines of the dorsal fin, from
   eleven to thirteen in number, can be received in a groove; anal
   spines three.

Seven species are known, the majority of which are European, as
_P. erythrinus_, common in the Mediterranean, and not rare on the
south coast of England, where it is generally termed “Becker;”
_P. centrodontus_, the common “Sea-bream” of the English coasts,
distinguished by a black spot on the origin of the lateral line; in the
young, which are called “Chad” by Cornish and Devon fishermen, this
spot is absent; _P. owenii_, the “Axillary or Spanish Sea-Bream,”
likewise from the British coasts. _Pagellus lithognathus_, from the
coasts of the Cape of Good Hope, attains to a length of four feet, and
is one of the fishes which are dried for export and sale to whalers.

   CHRYSOPHRYS.--Body oblong, compressed, with scales of moderate
   size. Jaws with four or six canine teeth in front, and with
   three or more series of rounded molars on each side. Cheeks
   scaly. The spines of the dorsal fin, eleven or twelve in number,
   can be received in a groove; anal spines three.

Some twenty species are known from tropical seas and the warmer parts
of the temperate zones. Generally known is _Ch. aurata_, from the
Mediterranean, occasionally found on the south coast of England,
where it is named “Gilthead.” The French call it “Daurade,” no doubt
from the Latin _Aurata_, a term applied to it by ancient authors. The
Greeks named it Chrysophrys (_i.e._ golden eyebrow), in allusion to
the brilliant spot of gold which it bears between its eyes. According
to Columella, the Aurata was among the number of the fishes brought
up by the Romans in their vivaria; and the inventor of those vivaria,
one Sergius Orata, is supposed to have derived his surname from
this fish. It is said to grow extremely fat in artificial ponds.
Duhamel states that it stirs up the sand with the tail, so as to
discover the shell-fish concealed in it. It is extremely fond of
mussels, and its near presence is sometimes ascertained by the noise
which it makes while breaking their shells with its teeth. Several
species found on the Cape of Good Hope attain to as large a size as
_Pagellus lithognathus_, and are preserved for sale like that species.
_Chrysophrys hasta_ is one of the most common species of the East
Indian and Chinese coasts, and enters large rivers.

_Fifth Group--Pimelepterina._--In both jaws a single anterior series
of cutting teeth, implanted by a horizontal posterior process, behind
which is a band of villiform teeth. Villiform teeth on the vomer,
palatines and the tongue. Vertical fins densely covered with minute
scales. Only one genus is known, _Pimelepterus_, with six species from
tropical seas. These fishes are sometimes found at a great distance
from the land.


                     FIFTH FAMILY--HOPLOGNATHIDÆ.

_Body compressed and elevated, covered with very small ctenoid scales.
Lateral line continuous. The bones of the jaws have a sharp dentigerous
edge, as in Scarus. The teeth, if at all conspicuous, being continuous
with the bone, forming a more or less indistinct serrature; no teeth
on the palate. The spinous portion of the dorsal fin is rather more
developed than the soft; the spines strong; anal with three spines,
similar to the soft dorsal. Ventrals thoracic, with one spine and five
soft rays._

One genus only is known, _Hoplognathus_, with four species from
Australian, Japanese, and Peruvian coasts.

  [Illustration: Fig. 176.--Teeth of Hoplognathus.]


                       SIXTH FAMILY--CIRRHITIDÆ.

_Body oblong, compressed, covered with cycloid scales; lateral
line continuous. Mouth in front of the snout, with lateral cleft.
Eye lateral, of moderate size. Cheeks without a bony stay for the
præoperculum. Generally six, sometimes five or three branchiostegals.
Dentition more or less complete, composed of small pointed teeth,
sometimes with the addition of canines. One dorsal fin, formed by a
spinous and soft portion, of nearly equal development. Anal with three
spines, generally less developed than the soft dorsal. The lower rays
of the pectoral fins simple and generally enlarged; ventrals thoracic,
but remote from the root of the pectorals, with one spine and five
rays._

The fishes of this family may be readily recognised by their
thickened, undivided lower pectoral rays, which in some are evidently
auxiliary organs of locomotion, in others, probably, organs of
touch. They differ from the following family, the Scorpænidæ, in
lacking the bony connection between the infraorbital ring and the
præoperculum. Two groups may be distinguished in this family, which,
however, are connected by an intermediate genus (_Chironemus_). The
first, distinguished by the presence of vomerine teeth, consists of
_Cirrhites_ and _Chorinemus_, small prettily coloured fishes. The
former genus is peculiar to the Indo-Pacific, and consists of sixteen
species; the second, with three species, seems to be confined to
the coasts of Australia and New Zealand. The second group lacks the
vomerine teeth, and comprises the following genera:--

   CHILODACTYLUS.--One dorsal fin, with from sixteen to nineteen
   spines; anal fin of moderate length; caudal forked. One of the
   simple pectoral rays more or less prolonged, and projecting
   beyond the margin of the fin. Teeth in villiform bands; no
   canines. Præoperculum not serrated. Scales of moderate size.
   Air-bladder with many lobes.

  [Illustration: Fig. 177.--_Chilodactylus macropterus_, from
  Australia.]

Seventeen species are known, chiefly from the temperate parts of the
Southern Pacific, and also from the coasts of Japan and China. They
belong to the most valuable food-fishes, as they grow to a considerable
size (from five to twenty-five lbs.), and are easily caught in
numbers. At the Cape of Good Hope they are very abundant, and preserved
in large quantities for export.

_Mendosoma_ from the coast of Chili, and _Nemadactylus_ from Tasmania,
are allied genera.

   LATRIS.--Dorsal fin deeply notched; the spinous portion with
   seventeen spines; anal fin many-rayed. None of the simple
   pectoral rays passes the margin of the fin. Teeth villiform; no
   canines. Præoperculum minutely serrated. Scales small.

Two species only are known from Tasmania and New Zealand, which belong
to the most important food-fishes of the Southern Hemisphere. _Latris
hecateia_ or the “Trumpeter,” ranges from sixty to thirty lbs. in
weight, and is considered by the colonists the best flavoured of any of
the fishes of South Australia, Tasmania, and New Zealand, and consumed
smoked as well as fresh. The second species, _Latris ciliaris_, is
smaller, scarcely attaining a weight of twenty lbs., but more abundant;
it is confined to the coast of New Zealand.

  [Illustration: Fig. 178.--Skull of _Scorpæna percoides_;
  _so_, Suborbital ring; _pr_, Præoperculum; _st_,
  Bony stay, connecting the sub-orbital with the præoperculum.]


                      SEVENTH FAMILY--SCORPÆNIDÆ.

_Body oblong, more or less compressed, covered with ordinary scales,
or naked. Cleft of the mouth lateral or subvertical. Dentition feeble,
consisting of villiform teeth; and generally without canines. Some
bones of the head armed, especially the angle of the præoperculum,
its armature receiving additional support by a bony stay, connecting
it with the infraorbital ring. The spinous portion of the dorsal fin
equally or more developed than the soft and than the anal. Ventrals
thoracic, generally with one spine and five soft rays, sometimes
rudimentary._

This family consists of carnivorous marine fishes only; some resemble
the Sea-Perches in form and habits, as _Sebastes_, _Scorpæna_, etc.,
whilst others live at the bottom of the sea, and possess in various
degrees of development those skinny appendages resembling the fronds of
seaweeds, by which they either attract other fishes, or by which they
are enabled more effectually to hide themselves. Species provided with
those appendages have generally a coloration resembling that of their
surroundings, and varying with the change of locality. The habit of
living on the bottom has also developed in many Scorpænoids separate
pectoral rays, by means of which they move or feel. Some of the genera
live at a considerable depth, but apparently not beyond 300 fathoms.
Nearly all are distinguished by a powerful armature either of the head,
or fin spines, or both; and in some the spines have been developed into
poison organs.

The only fossil representative known at present is a species of
_Scorpæna_ from the Eocene of Oran.

   SEBASTES.--Head and body compressed; crown of the head scaly to,
   or even beyond, the orbits; no transverse groove on the occiput.
   Body covered with scales of moderate or small size, and without
   skinny tentacles. Fin-rays not elongate; one dorsal, divided by
   a notch into a spinous and soft portion, with twelve or thirteen
   spines; the anal with three. No pectoral appendages. Villiform
   teeth in the jaws, on the vomer, and generally on the palatine
   bones. Vertebræ more than twenty-four.

About twenty species are known, principally from seas of the temperate
zones, as from the coasts of Northern Europe (_S. norvegicus_, _S.
viviparus_), of Japan, California, New Zealand, and Van Diemen’s Land.
All seem to prefer deep water to the surface, and _Sebastes macrochir_
has been obtained at a depth of 345 fathoms. In their general form
they resemble the Sea-Perches, attain to a weight of from one to four
lbs., and are generally esteemed as food.

   SCORPÆNA.--Head large, slightly compressed, generally with a
   transverse naked depression on the occiput; bones of the head
   armed with spines, and generally with skinny tentacles. Scales
   of moderate size. Mouth large, oblique. Villiform teeth in the
   jaws, and at least on the vomer. One dorsal, 12–13/9, A. 3/5.
   Pectoral fins without detached rays, large, rounded, with the
   lower rays simple and thickened. Air-bladder none. Vertebræ
   twenty-four.

  [Illustration: Fig. 179.--Head of Scorpæna percoides, from New
  Zealand.]

  [Illustration: Fig. 180.--Scorpæna bynoensis, from the coasts of
  Australia.]

About forty species are known from tropical and sub-tropical seas.
They lead a sedentary life, lying hidden in the sand, or between rocks
covered with seaweed, watching for their prey, which chiefly consists
of small fishes. Their strong undivided pectoral rays aid them in
burrowing in the sand, and in moving along the bottom. The type of
their coloration is very much the same in all the species, viz. an
irregular mottling of red, yellow, brown, and black colours, but the
distribution of these colours varies exceedingly, not only in the same
species but also in the same individuals. They do not attain to any
considerable size, probably never exceeding a length of 18 inches.
Their flesh is well flavoured. Wounds inflicted by their fin-spines are
exceedingly painful, but not followed by serious consequences.

_Glyptauchen_ and _Lioscorpius_ are genera closely allied to
_Scorpæna_, from Australian seas.

_Setarches_ is also allied to the preceding genera, and provided with
very large eyes, in accordance with the depth (215 fathoms) which the
two species known at present inhabit; one has been found near Madeira,
the other near the Fiji Islands.

   PTEROIS.--Head and body compressed; scales of small or moderate
   size. Bones of the head armed with numerous spinous projections,
   between which often skinny tentacles are developed. The dorsal
   spines and pectoral rays are more or less prolonged, passing
   beyond the margin of the connecting membrane. Twelve or thirteen
   dorsal spines. Villiform teeth in the jaws and on the vomer.

Nine species are known from the tropical Indo-Pacific. They belong
to the most singularly formed and most beautifully coloured fishes
of the Tropics, and formerly were believed to be able to fly, like
Dactylopterus. But the membrane connecting their pectoral rays is
much too short and feeble to enable them to raise themselves from the
surface of the water.

   APISTUS.--Head and body compressed, covered with ctenoid scales
   of rather small size. Some bones of the head, and especially
   the præorbital, are armed with spines. One dorsal with fifteen
   spines; the anal with three. The pectoral fin is elongate, and
   one ray is completely detached from the fin. Villiform teeth in
   the jaws, on the vomer, and palatine bones. Air-bladder present.
   A cleft behind the fourth gill.

Two species from the Indian Ocean. These fishes are very small, but
of interest on account of the prolongation of their pectoral fins,
which indicates that they can take long flying leaps out of the water.
However, this requires confirmation by actual observation.

   AGRIOPUS.--Head and body compressed, scaleless; head without
   any, or with very feeble, armature. Cleft of the mouth small, at
   the end of the produced snout. One dorsal fin, which commences
   from the head, the spinous portion being formed by from
   seventeen to twenty-one strong spines; anal short. Villiform
   teeth in the jaws, generally none on the vomer.

Seven species. This singular genus is peculiar to the temperate parts
of the South Pacific, occurring at the Cape, on the coast of South
Australia, and Chili. The largest species (_A. torvus_) attains a
length of two and a half feet. Nothing is known of its mode of life.

   SYNANCEIA.--General appearance of the fish, especially of the
   head, monstrous. Scales none; skin with numerous soft warty
   protuberances or filaments. Mouth directed upwards, wide. Eyes
   small. From thirteen to sixteen dorsal spines; pectoral fins
   very large. Villiform teeth in the jaws, and sometimes on the
   vomer.

Four species are known from the Indo-Pacific, of which _S. horrida_ and
_S. verrucosa_ are the most generally distributed, and, unfortunately,
the most common. They are justly feared on account of the great danger
accompanying wounds which they inflict with their poisoned dorsal
spines, as has been already noticed above, p. 191. The greatest length
to which they attain does not seem to exceed eighteen inches. They are
very voracious fishes, and their stomach is of so great a capacity that
they are able to swallow fishes one-third of their own bulk.

   MICROPUS.--Head and body strongly compressed, short, and deep;
   no scales, but the skin is covered with minute tubercles. Snout
   very short, with nearly vertical anterior profile. Præorbital,
   præ- and inter-operculum with spines on the edge. Dorsal fin
   with seven or eight, anal with two spines. Pectorals short,
   ventrals rudimentary. Jaws with villiform teeth.

These fishes belong to the smallest of Acanthopterygians, scarcely
exceeding 1½ inches in length. Two species are known, which are rather
common on the coral reefs of the Pacific.

   CHORISMODACTYLUS.--Head and body rather compressed,
   scaleless, with skinny flaps. Bones of the head with prominent
   ridges; the præorbital, præoperculum, and operculum armed; a
   depression on the occiput. One dorsal fin, with thirteen spines;
   the anal with two. Three free pectoral appendages. Ventral fins
   with one spine and five rays. Villiform teeth in the jaws only.

Only one small species, _Ch. multibarbis_, is known, from the coasts of
India and China.

  [Illustration: Fig. 181.--Chorismodactylus multibarbis.]

To complete the list of Scorpænoid genera, we have to mention
_Tænianotus_, _Centropogon_, _Pentaroge_, _Tetraroge_, _Prosopodasys_,
_Aploactis_, _Trichopleura_, _Hemitripterus_, _Minous_ and _Pelor_.


                        EIGHTH FAMILY--NANDIDÆ.

_Body oblong, compressed, covered with scales. Lateral line
interrupted. Dorsal fin formed by a spinous and soft portion, the
number of spines and rays being nearly equal; anal fin with three
spines, and with the soft portion similar to the soft dorsal. Ventral
fins thoracic, with one spine, and five or four rays. Dentition more or
less complete, but feeble._

This small family consists of two very distinct groups.

A. _Plesiopina._ Marine fishes of small size, with pseudobranchiæ
and only four ventral rays. _Plesiops_ from the coral-reefs of the
Indo-Pacific, and _Trachinops_ from the coast of New South Wales,
belong to this group.

B. _Nandina._ Freshwater fishes of small size from the East Indies,
without pseudobranchiæ, and five ventral rays. The genera are _Badis_,
_Nandus_, and _Catopra_.


                      NINTH FAMILY--POLYCENTRIDÆ.

_Body compressed, deep, scaly. Lateral line none. Dorsal and anal
fins long, both with numerous spines, the spinous portion being the
more developed. Ventrals thoracic, with one spine and five soft rays.
Teeth feeble. Pseudobranchiæ hidden._

Only two genera, each represented by one or two species in the Atlantic
rivers of Tropical America, _Polycentrus_ and _Monocirrhus_,
belong to this family. They are small insectivorous fishes.


                       TENTH FAMILY--TEUTHIDIDÆ.

_Body oblong, strongly compressed, covered with very small scales.
Lateral line continuous. Eye lateral, of moderate size. A single series
of cutting incisors in each jaw; palate toothless. One dorsal fin,
the spinous portion being the more deve__loped; anal with seven
spines. Ventral fins thoracic, with an outer and an inner spine, and
with three soft rays between._

This family consists of one very natural genus, _Teuthis_, readily
recognised by the singular structure of the fins. In all the species
the fin-formula is D. 13/10. A. 7/9. The incisors are small, narrow,
and provided with a serrated edge. The air-bladder is large, and
forked anteriorly as well as posteriorly. Their skeleton shows several
peculiarities: the number of vertebræ is twenty-three, ten of which
belong to the abdominal portion. The abdominal cavity is surrounded
by a complete ring of bones, the second piece of the coracoid being
exceedingly long, and extending along the whole length of the abdomen,
where it is joined to a spinous process of the first interhæmal. The
pubic bones are slender, long, firmly attached to each other, without
leaving a free space between them. They are fastened by a long process
which passes the symphysis of the radii, and extends on to that of the
humeri.

  [Illustration: Fig. 182.--Teuthis nebulosa, Indian Ocean.]

Thirty species are known, all from the Indo-Pacific; but they do not
extend eastwards beyond 140° long., or to the Sandwich Islands. They
are herbivorous, and do not exceed a length of fifteen inches.


            SECOND DIVISION--ACANTHOPTERYGII BERYCIFORMES.

_Body compressed, oblong, or elevated; head with large muciferous
cavities which are covered with a thin skin. Ventral fins thoracic,
with one spine and more than five soft rays_ (_in_ Monocentris _with
two only_).

One family only belongs to this division.


                           FAMILY--BERYCIDÆ.

_Body short, with ctenoid scales, which are rarely absent. Eyes
lateral, large_ (_except_ Melamphaës). _Cleft of the mouth lateral,
oblique; jaws with villiform teeth; palate generally toothed. Opercular
bones more or less armed. Eight (four) branchiostegals._

This family offers several points of biological interest. All
its members are strictly marine; but only two of the genera are
surface-forms (_Holocentrum_ and _Myripristis_). All the others
descend considerably below the surface, and even some of the species
of _Myripristis_ habitually inhabit depths of from 50 to 100 fathoms.
_Polymixia_ and _Beryx_ have been found in 345 fathoms. _Melamphaës_
must live at a still greater depth, as we may infer from the small
size of its eye; this fish is not likely to come nearer to the surface
than to about 200 fathoms. The other genera named have extremely large
eyes, and, therefore, may be assumed to ascend into such superficial
strata as are still lit up by a certain proportion of sun-rays. The
highly-developed apparatus for the secretion of superficial mucus, with
which these fishes are provided, is another sign of their living at a
greater depth than any of the preceding families of Acanthopterygians.
In accordance with this vertical distribution, Berycoid fishes have a
wide horizontal range, and several species occur at Madeira as well as
in Japan.

Fossil Berycoids show a still greater diversity of form than living;
they belong to the oldest Teleosteous fishes, the majority of the
Acanthopterygians found in the chalk being representatives of this
family. _Beryx_ has been found in several species, with other genera
now extinct: _Pseudoberyx_, with abdominal ventrals, from Mount
Lebanon; _Berycopsis_, with cycloid scales; _Homonotus_, _Stenostoma_,
_Sphenocephalus_, _Acanus_, _Hoplopteryx_, _Platycornus_, with
granular scales; _Podocys_, with a dorsal fin extending to the neck;
_Acrogaster_, _Macrolepis_, and _Rhacolepis_, from the chalk of Brazil.
Species of _Holocentrum_ and _Myripristis_ occur in the Monte Bolca
formation.

   MONOCENTRIS.--Snout obtuse, convex, short; eye of moderate size.
   Villiform teeth on the palatine bones, but none on the vomer.
   Opercular bones without armature. Scales very large, bony,
   forming a rigid carapace. Ventrals reduced to a single strong
   spine and a few rudimentary rays.

  [Illustration: Fig. 183.--Monocentris japonicus.]

One species only is known (_M. japonicus_) from the seas off Japan
and Mauritius. It does not attain to any size, and is not common.

   HOPLOSTETHUS.--Snout very short and obtuse; eye large.
   Villiform teeth on the palatine bones, but none on the vomer.
   Operculum unarmed, a strong spine at the scapulary and the angle
   of the præoperculum. Scales ctenoid, of moderate size; abdominal
   edge serrated. One dorsal, with six spines; ventrals with six
   soft rays; caudal deeply forked.

One species only is known (_H. mediterraneus_), which occurs in the
Mediterranean, the neighbouring parts of the Atlantic, and in the sea
off Japan.

   TRACHICHTHYS.--Snout very short and obtuse, with prominent chin;
   eye large. Villiform teeth on the palatine bones and on the
   vomer. A strong spine at the scapulary and at the angle of the
   præoperculum. Scales rather small; abdomen serrated. One dorsal,
   with from three to six spines; ventral with six soft rays.
   Caudal forked.

Four species are known from New Zealand and Madeira.

_Anoplogaster_ is an allied genus from tropical parts of the
Atlantic; it is scaleless.

   BERYX.--Snout short, with oblique cleft of the mouth and
   prominent chin; eye large. Villiform teeth on the palatine bones
   and vomer. Opercular bones serrated; no spine at the angle of
   the præoperculum. Scales ctenoid, of moderate or large size. One
   dorsal, with several spines; ventrals with seven or more soft
   rays. Anal with four spines; caudal forked.

  [Illustration: Fig. 184.--Beryx decadactylus.]

Five species are known from Madeira, the tropical Atlantic, and
the seas of Japan and Australia. The species figured is _B.
decadactylus_, common at Madeira, and occurring near Japan at a
depth of 345 fathoms; it attains a length of 1½ feet.

   MELAMPHAES.--Head large and thick, with very thin bones, nearly
   all the superficial bones being transformed into wide muciferous
   channels. Eye small. Palate toothless; no barbels; opercles not
   armed. Scales large, cycloid. One dorsal, with six spines; anal
   spines very feeble; caudal forked. Ventrals with seven rays.

Two species, deep-sea fishes of the Atlantic; they are very scarce, as
only three or four specimens have been found hitherto.

   POLYMIXIA.--Snout short, with the cleft of the mouth nearly
   horizontal; eye large. Two barbels at the throat. Opercles
   without armature. Scales of moderate size. One dorsal. Anal with
   three or four spines; caudal forked; ventrals with six or seven
   soft rays.

Three species are known: _P. nobilis_ from Madeira and St. Helena, _P.
lowei_ from Cuba, and _P. japonica_ from Japan; the latter species from
a depth of 345 fathoms. Average size eighteen inches.

   MYRIPRISTIS.--Snout short, with oblique cleft of the mouth and
   prominent chin; eye large or very large. Villiform teeth on the
   vomer and palatine bones. Opercular bones serrated; præoperculum
   without spine. Scales large, ctenoid. Two dorsals, the first
   with ten or eleven spines; anal with four spines; caudal
   forked; ventrals with seven soft rays. Air-bladder divided by
   a contraction in two parts, the anterior of which is connected
   with the organ of hearing.

Eighteen species from the tropical seas of both hemispheres, the
majority living near the coast at the surface. The coloration is
(principally) red or pink on the back and silvery on the sides. They
attain a length of about 15 inches, and are esteemed as food.

   HOLOCENTRUM.--Snout somewhat projecting, with the cleft of
   the mouth nearly horizontal; eye large. Villiform teeth on
   the vomer and palatine bones. Opercular bones and præorbital
   serrated; operculum with two spines behind; a large spine at the
   angle of the præoperculum. Scales ctenoid, of moderate size. Two
   dorsals, the first with twelve spines; anal with four spines,
   the third being very long and strong; caudal forked. Ventrals
   with seven soft rays.

  [Illustration: Fig. 185.--_Holocentrum unipunctatum_, from
  the South Sea.]

About thirty species are known from the tropical seas of both
hemispheres; all are surface fishes, and very common. The young have
the upper part of the snout pointed and elongate, and were described as
a distinct genus (_Rhynchichthys_). The coloration of the adult is
uniform; red, pink, and silvery prevailing. They attain to a length of
about 15 inches, and are esteemed as food.


             THIRD DIVISION--ACANTHOPTERYGII KURTIFORMES.

_One dorsal fin only, much shorter than the anal, which is long and
many-rayed. No superbranchial organ._

One family only belongs to this division.


                           FAMILY--KURTIDÆ.

_Body compressed, oblong, deep in front, attenuated behind. Snout
short. The spines of the short dorsal are few in number, if developed.
Scales small or of moderate size. Villiform teeth in the jaws, on the
vomer, and palatine bones._

This family consists of a small number of species only, which form
two distinct genera, _Pempheris_ and _Kurtus_. They are shore fishes
of tropical seas. In both the air-bladder shows some peculiarity: in
_Pempheris_ it is divided into an anterior and posterior portion; in
_Kurtus_ it is lodged within the ribs, which are dilated, convex,
forming rings. The number of vertebræ is respectively twenty-four and
twenty-three.


           FOURTH DIVISION--ACANTHOPTERYGII POLYNEMIFORMES.

_Two rather short dorsal fins, somewhat remote from each other; free
filaments at the humeral arch, below the pectoral fins; muciferous
canals of the head well developed._

One family only belongs to this division.


                          FAMILY--POLYNEMIDÆ.

_Body oblong, rather compressed, covered with smooth or very feebly
ciliated scales. Lateral line continuous. Snout projecting beyond the
mouth, which is inferior, with lateral cleft. Eye lateral, large.
Villiform teeth in the jaws and on the palate. Ventrals thoracic, with
one spine and five rays._

The fishes of this natural family have been divided, on slight
differences, into three genera--_Polynemus_, _Pentanemus_, and
_Galeoides_. They are found in rather numerous species on the coasts
between the tropics, and the majority enter brackish or even fresh
water. Very characteristic are the free filaments which in this family
are organs of touch; they are inserted on the humeral arch at some
distance from the pectoral fin; but, nevertheless, can be regarded
only as a detached portion of that fin; they can be moved quite
independently of the fin; their number varies from three to fourteen,
according to the species; in some they are exceedingly elongate, twice
as long as the fish, in others they are not longer or even shorter than
the pectoral. It is evident from the whole organisation of these fishes
that they live on muddy bottom or in thick water, such as is found
near the mouths of great rivers. Their eyes are large, but generally
obscured by a filmy skin, so that those feelers must be of great use
to them in finding their way and their food. The Polynemoids are very
useful to man: their flesh is esteemed, and some of the species are
provided with an air-bladder which yields a good sort of isinglass,
and forms an article of trade in the East Indies. Some of these fishes
attain to a length of four feet.

  [Illustration: Fig. 186.--_Pentanemus quinquarius_, from the
  West Coast of Africa and the West Indies.]


             FIFTH DIVISION--ACANTHOPTERYGII SCIÆNIFORMES.

_The soft dorsal is more, generally much more, developed than the
spinous, and than the anal. No pectoral filaments; head with the
muciferous canals well developed._

Also this division is composed of one family only.


                           FAMILY--SCIÆNIDÆ.

_Body rather elongate, compressed, covered with ctenoid scales.
Lateral line continuous, and frequently extending over the caudal fin.
Mouth in front of the snout. Eye lateral, of moderate size. Teeth in
villiform bands, sometimes with the addition of canines; no molars or
incisor-like teeth in the jaws; palate toothless. Præoperculum unarmed,
and without bony stay. Ventrals thoracic, with one spine and five soft
rays. Bones of the head with wide muciferous channels. Stomach coecal.
Air-bladder frequently with numerous appendages_ (see pp. 144 and
_seq._)

The fishes of the “_Meagre_” family are chiefly coast-fishes of the
tropical and sub-tropical Atlantic and Indian Oceans, preferring the
neighbourhood of the mouths of large rivers, into which they freely
enter, some of the species having become so completely naturalised in
fresh water that they are never found nowadays in the sea. Some of the
larger species wander far from their original home, and are not rarely
found at distant localities as occasional visitors. In the Pacific
and on the coast of Australia, where but a few large rivers enter the
ocean, they are extremely rare and, in the Red Sea, they are absent.
Many attain a large size, and almost all are eaten.

No fossil species have been as yet discovered.

   POGONIAS.--Snout convex, with the upper jaw overlapping the
   lower. Mandible with numerous small barbels. No canines. The
   first dorsal with ten stout spines. Two anal spines, the second
   very strong. Scales of moderate size.

To this fish (_P. chromis_) more especially is given the name of
“Drum,” from the extraordinary sounds which are produced by it and
other allied Sciænoids. These sounds are better expressed by the word
drumming than by any other, and are frequently noticed by persons in
vessels lying at anchor on the coasts of the United States, where those
fishes abound. It is still a matter of uncertainty by what means the
“Drum” produces the sounds. Some naturalists believe that it is caused
by the clapping together of the pharyngeal teeth, which are very large
molar teeth. However, if it be true that the sounds are accompanied
by a tremulous motion of the vessel, it seems more probable that they
are produced by the fishes beating their tails against the bottom of
the vessel in order to get rid of the parasites with which that part
of their body is infested. The “Drum” attains to a length of more than
four feet, and to a weight exceeding a hundred lbs. Its air-bladder has
been figured on p. 146.

_Micropogon_ is closely allied to _Pogonias_, but has conical
pharyngeal teeth. Two species from the western parts of the Atlantic.

  [Illustration: Fig. 187.--Pharyngeal bones and teeth of
  _Pogonias chromis_. A, Upper; B, Lower pharyngeals.]

   UMBRINA.--Snout convex, with the upper jaw overlapping the
   lower; a short barbel under the symphysis of the mandible. The
   first dorsal with nine or ten flexible spines, the anal with one
   or two. Scales of moderate size.

  [Illustration: Fig. 188.--_Umbrina nasus_, from Panama.]

Twenty species are known from the Mediterranean, Atlantic, and Indian
Ocean. One well known to the ancients, under the name of _Umbra_, is
the _Umbrina cirrhosa_ of the Mediterranean, the “Umbrine” or “Ombre”
of the French, and the “Corvo” of the Italians. It ranges to the Cape
of Good Hope, and attains a length of three feet. Also on the coasts
of the United States several species occur, as _U. alburna_, _U.
nebulosa_, etc.

  [Illustration: Fig. 189.--_Umbrina nasus_, from Panama.]

   SCIÆNA (including _Corvina_).--The upper jaw overlapping
   the lower, or both jaws equal in front. Interorbital space
   moderately broad and slightly convex. Cleft of the mouth
   horizontal or slightly oblique. The outer series of teeth is
   generally composed of teeth larger than the rest, but there are
   no canines. Eye of moderate size, barbel none.

  [Illustration: Fig. 190.--Sciæna richardsonii.]

Some fifty species are known, but their distinctive characters have
been but imperfectly pointed out. They are found in all the seas
and rivers in which Sciænoids generally occur, and many are entirely
confined to fresh water, for instance the species figured, _Sciæna
richardsonii_, from Lake Huron; _Sc. amazonica_; _Sc. obliqua_,
_ocellata_, _oscula_, etc., from fresh waters of the United States.
_Sciæna diacanthus_ and _Sc. coitor_ belong to the most common fishes
of the coasts of the East Indies, ascending the great rivers for a long
distance from the sea. One of the European species, _Sciæna aquila_,
has an extremely wide range; it not rarely reaches the British coasts,
where it is known as “Meagre,” and has been found at the Cape of Good
Hope and on the coast of southern Australia. Like some of the other
species it attains to a length of six feet, but the majority of the
species of this genus remain within smaller dimensions. A part of the
species have the second anal ray very strong, and have been placed into
a distinct genus, _Corvina_,--thus, among others, _Sc. nigra_ from the
Mediterranean, and _Sc. richardsonii_.

_Pachyurus_ is closely allied to _Sciæna_, but has the vertical fins
densely covered with small scales.

   OTOLITHUS.--Snout obtuse or somewhat pointed, with the lower jaw
   longer. The first dorsal with nine or ten feeble spines. Canine
   teeth more or less distinct. Præoperculum denticulated. Scales
   of moderate or small size.

About twenty species are known from the tropical and sub-tropical parts
of the Atlantic and Indian Oceans. The air-bladder is figured on p. 144.

   ANCYLODON differs from _Otolithus_ in having very long
   arrow-shaped or lanceolate canine teeth. Coasts of tropical
   America.

   COLLICHTHYS.--Body elongate; head very broad, with the upper
   surface very convex; cleft of the mouth wide and oblique;
   no large canines. Eye small. No barbel. Scales small, or of
   moderate size. The second dorsal very long, caudal pointed.

Three species from the East Indian and Chinese coasts. The great
development of the muciferous system on the head and the small eye
leads one to suppose that these fishes live in muddy water near the
mouths of large rivers. The air-bladder has been described on p. 144.

Other genera belonging to this family are _Larimus_, _Eques_, _Nebris_,
and _Lonchurus_.

  [Illustration: Fig. 191.--Histiophorus pulchellus.]


             SIXTH DIVISION--ACANTHOPTERYGII XIPHIIFORMES.

_The upper jaw is produced into a long cuneiform weapon._

These fishes form one small family only, _Xiphiidæ_.

The “Sword-fishes” are pelagic fishes, occurring in all tropical and
sub-tropical seas. Generally found in the open ocean, always vigilant,
and endowed with extraordinary strength and velocity, they are but
rarely captured, and still more rarely preserved. The species found
in the Indian and Pacific Oceans belong to the genus _Histiophorus_,
distinguished from the common Mediterranean Sword-fish, or _Xiphias_,
by the presence of ventral fins, which, however, are reduced to two
long styliform appendages. The distinction of the species is beset with
great difficulties, owing to the circumstance that but few examples
exist in museums, and further, because the form of the dorsal fin,
the length of the ventrals, the shape and length of the sword, appear
to change according to the age of the individuals. Some specimens or
species have only the anterior dorsal rays elevated, the remainder of
the fin being very low, whilst in others all the rays are exceedingly
elongate, so that the fin, when erected, projects beyond the surface of
the water. It is stated that Sword-fishes, when quietly floating with
the dorsal fin erect, can sail before the wind, like a boat.

Sword-fishes are the largest of Acanthopterygians, and not exceeded in
size by any other Teleostean; they attain to a length of from 12 to 15
feet, and swords have been obtained more than three feet long, and with
a diameter of at least three inches at the base. The sword is formed by
the prolongation and coalescence of the maxillary and intermaxillary
bones; it is rough at its lower surface, owing to the development
of rudimentary villiform teeth, very hard and strong, and forms a
most formidable weapon. Sword-fishes never hesitate to attack whales
and other large Cetaceans, and by repeatedly stabbing these animals
generally retire from the combat victorious. The cause which excites
them to those attacks is unknown; but they follow this instinct so
blindly that they not rarely attack boats or large vessels in a similar
manner, evidently mistaking them for Cetaceans. Sometimes they actually
succeed in piercing the bottom of a ship, endangering its safety; but
as they are unable to execute powerful backward movements they cannot
always retract their sword, which is broken off by the exertions of the
fish to free itself. A piece of a two-inch plank of a whale-boat, thus
pierced by a sword-fish, in which the broken sword still remains, is
preserved in the British Museum.

The Rev. Wyatt Gill, who has worked as a missionary for many years in
the South Sea Islands, communicates that young Sword-fishes are easily
caught in strong nets, but no net is strong enough to hold a fish of
six feet in length. Specimens of that size are now and then captured
by hook and line, a small fish being used as bait. Individuals with
the sword broken off are not rarely observed. Larger specimens cannot
be captured by the natives, who are in great fear of them. They easily
pierce their canoes, and only too often dangerously wound persons
sitting in them.

The Mediterranean Sword-fish is constantly caught in the nets of the
Tunny-fishers off the coast of Sicily, and brought to market, where its
flesh sells as well as that of the Tunny.

The remarkable changes which Sword-fishes undergo at an early stage of
their growth have been noticed above, p. 173 and _seq._

Sword-fishes are as old a type as the Berycoids. Their remains have
been found in the chalk of Lewes, and more frequently in the London
clay of Sheppy, where an extinct genus, _Coelorhynchus_, has been
recognised.


          SEVENTH DIVISION--ACANTHOPTERYGII TRICHIURIFORMES.

_Body elongate, compressed or band-like; cleft of the mouth wide,
with several strong teeth in the jaws or on the palate. The spinous
and soft portions of the dorsal fin and the anal are of nearly equal
extent, long, many-rayed, sometimes terminating in finlets; caudal fin
forked, if present._


                         FAMILY--TRICHIURIDÆ.

Marine fishes inhabiting the tropical and sub-tropical seas; some of
them are surface-fishes, living in the vicinity of the coast, whilst
others descend to moderate depths, as the Berycoids. All are powerful
rapacious fishes, as is indicated by their dentition.

The oldest of the extinct genera are _Enchodus_ and _Anenchelum_; they
were formerly referred to the Scombroids, but belong to this family.
The former has been found in the chalk of Lewes and Mæstricht; the
latter is abundant in the Eocene schists of Glaris. _Anenchelum_ is
much elongate, and exhibits in the slender structure of its bones the
characteristics of a deep-sea fish; it resembles much _Lepidopus_,
but has some long rays in the ventrals. Other Eocene genera are
_Nemopteryx_ and _Xiphopterus_. In the Miocene of Licata in Sicily
_Trichiuridæ_ are well represented, viz. by a species of _Lepidopus_,
and by two genera, _Hemithyrsites_ and _Trichiurichthys_, which are
allied to _Thyrsites_ and _Trichiurus_, but covered with scales.

The following is a complete list of the genera referred to this
family:--

   NEALOTUS.--Body incompletely clothed with delicate scales. Small
   teeth in the jaws and on the palatine bones; none on the vomer.
   Two dorsal fins, the first continuous and extending to the
   second; finlets behind the second and anal fins. Each ventral
   fin represented by a single small spine. A dagger-shaped spine
   behind the vent. Caudal fin well developed.

One specimen only of this fish (_N. tripes_), 10 inches long, has
been obtained off Madeira; it evidently lives at a considerable depth,
and comes to the surface only by accident.

   NESIARCHUS.--Body covered with small scales. Several strong
   fangs in the jaws; no teeth on the palate. First dorsal not
   extending to the second. No detached finlets. Ventrals small,
   but perfectly developed, thoracic. Caudal fin present. A
   dagger-shaped spine behind the vent.

A rather large fish (_N. nasutus_), very rarely found in the sea
off Madeira. The two or three specimens found hitherto measure from
three to four feet in length. Probably living at the same depth as the
preceding genus.

   APHANOPUS.--Scales none. Two very long dorsal fins; caudal well
   developed; ventrals none. A strong dagger-shaped spine behind
   the vent. Strong teeth in the jaws; none on the palate.

One species only is known, named _A. carbo_ from its coal-black
colour; it is evidently a deep-sea fish, very rarely obtained in the
sea off Madeira. Upwards of four feet long.

   EUOXYMETOPON.--Body naked, very long and thin. Profile of the
   head regularly decurved from the nape to the snout, the occiput
   and forehead being elevated and trenchant. Jaws with fangs;
   palatine teeth present. One dorsal only, continued from the head
   to the caudal fin, which is distinct. A dagger-shaped spine
   behind the vent. Pectoral fins inserted almost horizontally,
   with the lowest rays longest, and with the posterior border
   emarginate. Ventral fins rudimentary, scale-like.

This is another deep-sea form of this family, but, at present, no
observations have been made as regards the exact depth at which it
occurs. A specimen has been known since the year 1812; it was found on
the coast of Scotland, and described as _Trichiurus lepturus_. The
same species has been re-discovered in the West Indies, where, however,
it is also extremely scarce.

   LEPIDOPUS.--Body band-like; one single dorsal extends along
   the whole length of the back; caudal well developed. Ventrals
   reduced to a pair of scales. Scales none. Several fangs in the
   jaws; teeth on the palatine bones.

  [Illustration: Fig. 192.--Lepidopus caudatus.]

The Scabbard-fish (_L. caudatus_) is rather common in the Mediterranean
and warmer parts of the Atlantic, extending northwards to the south
coast of England, where it is an occasional visitor, and southwards
to the Cape of Good Hope. More recently it has been observed on the
coasts of Tasmania and New Zealand. We may, therefore, justly consider
it to be a deep-sea fish, which probably descends to the same depth as
the preceding allied forms. It grows to a length of five or six feet,
but its body is so much compressed that it does not weigh more than
as many pounds. It is well known in New Zealand, where it is called
“Frost-fish,” and esteemed as the most delicious fish of the colony.
A still more attenuated species (_L. tenuis_) occurs in the sea off
Japan, at a depth of some 340 fathoms.

   TRICHIURUS.--Body band-like, tapering into a fine point, without
   caudal fin. One single dorsal extending the whole length of the
   back. Ventrals reduced to a pair of scales, or entirely absent.
   Anal fin rudimentary, with numerous extremely short spines,
   scarcely projecting beyond the skin. Long fangs in the jaws;
   teeth on the palatine bones, none on the vomer.

The “Hairtails” belong to the tropical marine fauna, and although
generally found in the vicinity of land, they wander frequently out to
sea, perhaps merely because they follow some ocean-currents. Therefore
they are not rarely found in the temperate zone, the common West Indian
species (_T. lepturus_), for instance, on the coast of England. They
attain to a length of about four feet. The number of their vertebræ is
very large, as many as 160, and more. Six species are known.

   EPINNULA.--Body rather elongate, covered with minute scales,[*.
   see below] The first dorsal fin continuous, with spines of
   moderate strength, and extending on to the second; finlets none;
   ventrals well developed. Lateral lines two. Teeth of the jaws
   strong; palatine teeth, none.

The “Domine” of the Havannah, _E. magistralis_.

   THYRSITES.--Body rather elongate, for the greater part naked.
   The first dorsal continuous, with the spines of moderate
   strength, and extending on to the second. From two to six
   finlets behind the dorsal and anal. Several strong teeth in the
   jaws; teeth on the palatine bones.

The species of this genus attain to a considerable size (from four to
five feet), and are valuable food fishes; _Th. atun_ from the Cape
of Good Hope, South Australia, New Zealand, and Chili, is preserved,
pickled or smoked. In New Zealand it is called “Barracuda” or “Snoek,”
and exported from the colony into Mauritius and Batavia as a regular
article of commerce, being worth over £17 a ton; _Th. pretiosus_, the
“Escholar” of the Havannah, from the Mediterranean, the neighbouring
parts of the Atlantic, and the West Indies; _Th. prometheus_ from
Madeira, Bermuda, St. Helena, and Polynesia; _Th. solandri_ from
Amboyna and Tasmania is probably the same as _Th. prometheus_.

Young specimens of this (or, perhaps, the following) genus have been
described as _Dicrotus_. In them the finlets are not yet detached
from the rest of the fin; and the ventral fins, which are entirely
obsolete in the adult fish, are represented by a long crenulated spine.

   GEMPYLUS.--Body very elongate, scaleless. The first dorsal fin
   continuous, with thirty and more spines, and extending on to the
   second. Six finlets behind the dorsal and anal. Several strong
   teeth in the jaws, none on the palate.

One species (_G. serpens_), inhabiting considerable depths of the
Atlantic and Pacific Oceans.

                        FAMILY--PALÆORHYNCHIDÆ.

This family has been formed for two extinct genera:
_Palæorhynchus_ from the schists of Glaris, and
_Hemirhynchus_ from tertiary formations near Paris. These genera
resemble much the _Trichiuridæ_ in their long, compressed body,
and long vertical fins, but their jaws, which are produced into a long
beak, are toothless, or provided with very small teeth. The dorsal fin
extends the whole length of the back, and the anal reaches from the
vent nearly to the caudal, which is forked. The ventrals are composed
of several rays and thoracic. The vertebræ long, slender, and numerous,
and, like all the bones of the skeleton, thin, indicating that these
fishes were inhabitants of considerable depths of the ocean. Both
the jaws of _Palæorhynchus_ are prolonged into a beak, whilst in
_Hemirhynchus_ the upper exceeds the lower in length.


         EIGHTH DIVISION--ACANTHOPTERYGII COTTO-SCOMBRIFORMES.

_Spines developed, in one of the fins at least. Dorsal fins either
continuous or close together; the spinous dorsal, if present, always
short; sometimes modified into tentacles, or into a suctorial disk;
soft dorsal always long, if the spinous is absent; anal similarly
developed as the soft dorsal, and both generally much longer than
the spinous, sometimes terminating in finlets. Ventrals, thoracic or
jugular, if present, never modified into an adhesive apparatus. No
prominent anal papilla._

Marine fishes, with few exceptions.


                       FIRST FAMILY--ACRONURIDÆ.

_Body compressed, oblong or elevated, covered with minute scales.
Tail generally armed with one or more bony plates or spines, which
are developed with age, but absent in very young individuals. Eye
lateral, of moderate size. Mouth small; a single series of more or
less compressed, sometimes denticulated, sometimes pointed incisors in
each jaw; palate toothless. One dorsal fin, the spinous portion being
less developed than the soft; anal with two or three spines; ventral
fins thoracic. Air-bladder forked posteriorly. Intestines with more
or less numerous circumvolutions. Nine abdominal, and thirteen caudal
vertebræ._

Inhabitants of the tropical seas, and most abundant on coral-reefs.
They feed either on vegetable substances or on the superficial animal
matter of corals.

Extinct species of _Acanthurus_ and _Naseus_ have been discovered in
the Monte Bolca formation.

   ACANTHURUS.--Jaws with a single series of lobate incisors, which
   are sometimes movable. An erectile spine hidden in a groove on
   each side of the tail. Ventral fins with one spine and generally
   five rays. Scales ctenoid, sometimes with minute spines.
   Branchiostegals five.

The fishes of this genus, which sometimes are termed “Surgeons,”
are readily recognised by the sharp lancet-shaped spine with which
each side of the tail is armed. When at rest the spine is hidden
in a sheath; but it can be erected and used by the fish as a very
dangerous weapon, by striking with the tail towards the right and
left. “Surgeons” occur in all tropical seas, with the exception of the
eastern part of the Pacific, where they disappear with the corals. They
do not attain to any size, the largest species scarcely exceeding a
length of eighteen inches. Many are agreeably or showily coloured, the
ornamental colours being distributed in very extraordinary patterns.
The larger species are eatable, and some even esteemed as food. It
is stated that the fry of some species periodically approaches, in
immense numbers, the coasts of some of the South Sea Islands (Caroline
Archipelago), and serves as an important article of food to the
natives. Nearly fifty species are known.

  [Illustration: Fig. 193.--Acanthurus leucosternum, Indian Ocean.]

At an early period of their growth these fishes present so different an
aspect that they were considered a distinct genus, _Acronurus_.
The form of the body is more circular and exceedingly compressed. No
scales are developed, but the skin forms numerous oblique parallel
folds. The gill-cover and the breast are shining silvery.

   NASEUS.--Tail with two (rarely one or three) bony keeled plates
   on each side (in the adult). Head sometimes with a bony horn or
   crest-like prominence directed forwards. Ventral fins composed
   of one spine and three rays. From four to six spines in the
   dorsal; two anal spines. Scales minute, rough, forming a sort of
   fine shagreen. Air-bladder forked behind. Intestinal tract with
   many circumvolutions.

Twelve species are known from the tropical Indo-Pacific, but none
of them extend eastwards beyond the Sandwich Islands. In their mode
of life these fishes resemble the _Acanthuri_. Likewise, the young
have a very different appearance, and are unarmed, and were described
as a distinct genus, _Keris_. One of the most common species is _N.
unicornis_, which, when adult (22 inches long), has a horn about 2
inches long, whilst it is merely a projection in front of the eye in
individuals of 7 inches in length.

_Prionurus_ is an allied genus with a series of several keeled bony
laminæ on each side of the tail.

  [Illustration: Fig. 194.--Naseus unicornis.]


                       SECOND FAMILY--CARANGIDÆ.

_Body more or less compressed, oblong or elevated, covered with small
scales or naked; eye, lateral. Teeth, if present, conical. No bony
stay for the præoperculum. The spinous dorsal is less developed than
the soft or than the anal, either continuous with, or separated from,
the soft portion; sometimes rudimentary. Ventrals thoracic, sometimes
rudimentary or entirely absent. No prominent papilla near the vent.
Gill-opening wide. Ten abdominal and fourteen caudal vertebræ._

  [Illustration: Fig. 195.--Semiophoris velitans.]

Inhabitants of tropical and temperate seas. Carnivorous. They appear
first in cretaceous formations, where they are represented by
_Platax_ and some Caranx-like genera (_Vomer_ and _Aipichthys_ from
the chalk of Comen in Istria). They are more numerous in various
Tertiary formations, especially in the strata of Monte Bolca, where
some still existing genera occur, as _Zanclus_, _Platax_, _Caranx_
(_Carangopsis_), _Argyriosus_ (_Vomer_), _Lichia_, _Trachynotus_. Of
the extinct genera the following belong to this family:--_Pseudovomer_
(_Licata_), _Amphistium_, _Archæus_, _Ductor_, _Plionemus_ (?), and
_Semiophorus_. _Equula_ has been recently discovered in the Miocene
marls of Licata in Sicily.

   CARANX (including _Trachurus_).--Body more or less compressed,
   sometimes sub-cylindrical. Cleft of the mouth of moderate width.
   The first dorsal fin continuous, with about eight feeble spines,
   sometimes rudimentary; the soft dorsal and anal are succeeded
   by finlets in a few species. Two anal spines, somewhat remote
   from the fin. Scales very small. Lateral line with an anterior
   curved, and a posterior straight, portion, either entirely or
   posteriorly only covered by large plate-like scales, several
   of which are generally keeled, the keel ending in a spine.
   Dentition feeble. Air-bladder forked posteriorly.

  [Illustration: Fig. 196.--Plates of the lateral line of Caranx
  hippos.]

The “Horse-mackerels” are found in abundance in almost all temperate
and, especially, tropical seas. Many species wander to other parts
of the coast, or to some distance from land, and have thus gradually
extended their range over two or more oceanic areas; some are found
in all tropical seas. The species described are very numerous, about
ninety having been properly characterised and distinguished. Some
attain to a length of three feet and more, and all are eatable. They
feed on other fish and various marine animals.

Of the most noteworthy species the following may be mentioned:--_C.
trachurus_, the common British Horse-mackerel, distinguished by having
the lateral line in its whole length armed with large vertical plates;
it is almost cosmopolitan within the temperate and tropical zones
of the northern and southern hemispheres. _C. crumenophthalmus_,
_C. carangus_, and _C. hippos_, three of the most common sea-fishes,
equally abundant in the Atlantic and Indo-Pacific oceans; _C. ferdau_,
from the Indo-Pacific, upwards of three feet in length. _C. armatus_,
_ciliaris_, _gallus_, etc., which have an exceedingly short and
compressed body, with rudimentary spinous dorsal fin, and with some of
the rays of the dorsal and anal prolonged into filaments.

  [Illustration: Fig. 197.--Caranx ferdau.]

   ARGYRIOSUS is closely allied to _Caranx_, especially to the
   last-named species, but the lateral line has no plates whatever;
   and the body is scaleless, chiefly of a bright silvery colour.

Two species from the tropical Atlantic.

   MICROPTERYX.--Body much compressed, with prominent trenchant
   abdomen, covered with small scales; lateral line not shielded;
   præopercular margin entire. Cleft of the mouth rather small;
   præorbital of moderate width. The first dorsal continuous, with
   seven feeble spines. No detached finlets. Small teeth on the
   vomer and palatine bones.

_Micropteryx chrysurus_ is a semi-pelagic fish, and very common in
the tropical Atlantic, less so in the Indian Ocean.

   SERIOLA.--Body oblong, slightly compressed, with rounded
   abdomen, covered with very small scales; lateral line not
   shielded; præopercular margin entire. Cleft of the mouth of
   moderate width, or rather wide. The first dorsal continuous,
   with feeble spines. No detached finlets. Villiform teeth in the
   jaws, on the vomer and palatine bones.

These fishes are often called “Yellow-tails,” and occur in nearly
all the temperate and tropical seas, sometimes at a great distance
from land. Twelve species are known, and the majority have a wide
geographical range. The larger grow to a length of from four to five
feet, and are esteemed as food, especially at St. Helena, the Cape of
Good Hope, in Japan, Australia, and New Zealand.

_Seriolella_ and _Seriolichthys_, the latter from the Indo-Pacific, and
distinguished by a finlet behind the dorsal and anal, are allied genera.

   NAUCRATES.--Body oblong, sub-cylindrical, covered with
   small scales; a keel on each side of the tail. The spinous
   dorsal consists of a few short free spines; finlets none.
   Villiform teeth in the jaws, on the vomer and palatine bones.

The “Pilot-fish” (_N. ductor_) is a truly pelagic fish, known in
all tropical and temperate seas. Its name is derived from its habit of
keeping company with ships and large fish, especially Sharks. It is the
_Pompilus_ of the ancients, who describe it as pointing out the
way to dubious or embarrassed sailors, and as announcing the vicinity
of land by its sudden disappearance. It was therefore regarded as a
sacred fish. The connection between the Shark and the Pilot-fish has
received various interpretations, some observers having perhaps added
more sentiment than is warranted by the actual facts. It was stated
that the Shark never seized the Pilot-fish, that the latter was of
great use to its big companion in conducting it and showing it the way
to its food. Dr. Meyen in his “Reise um die Erde” states: “The pilot
swims constantly in front of the Shark; we ourselves have seen three
instances in which the Shark was led by the Pilot. When the Shark
neared the ship the Pilot swam close to the snout, or near one of the
pectoral fins of the animal. Sometimes he darted rapidly forwards or
sidewards as if looking for something, and constantly went back again
to the Shark. When we threw overboard a piece of bacon fastened on a
great hook, the Shark was about twenty paces from the ship. With the
quickness of lightning the Pilot came up, smelt at the dainty, and
instantly swam back again to the Shark, swimming many times round his
snout and splashing, as if to give him exact information as to the
bacon. The Shark now began to put himself in motion, the Pilot showing
him the way, and in a moment he was fast upon the hook.[42] Upon a
later occasion we observed two Pilots in sedulous attendance on a Blue
Shark, which we caught in the Chinese Sea. It seems probable that the
Pilot feeds on the Sharks’ excrements, keeps his company for that
purpose, and directs his operations solely from this selfish view.” We
believe that Dr. Meyen’s opinion, as expressed in his last words, is
perfectly correct. The Pilot obtains a great part of his food directly
from the Shark, in feeding on the parasitic crustaceans with which
Sharks and other large fish are infested, and on the smaller pieces of
flesh which are left unnoticed by the Shark when it tears its prey.
The Pilot also, being a small fish, obtains greater security when in
company of a Shark, which would keep at a distance all other fishes of
prey that would be likely to prove dangerous to the Pilot. Therefore,
in accompanying the Shark, the Pilot is led by the same instinct which
makes it follow a ship. With regard to the statement that the Pilot
itself is never attacked by the Shark all observers agree as to its
truth; but this may be accounted for in the same way as the impunity
of the swallow from the hawk, the Pilot-fish being too nimble for the
unwieldy Shark.

The Pilot-fish does not always leave the vessels on their approach
to land. In summer, when the temperature of the sea-water is several
degrees above the average, Pilots will follow ships to the south
coast of England into the harbour, where they are generally speedily
caught. Pilot-fish attain a length of 12 inches only. When very young
their appearance differs so much from the mature fish that they have
been described as a distinct genus, _Nauclerus_. This fry is
exceedingly common in the open ocean, and constantly obtained in the
tow-net; therefore the Pilot-fish retains its pelagic habits also
during the spawning season, and some of the spawn found by voyagers
floating on the surface is, without doubt, derived from this species.

CHORINEMUS.--Body compressed, oblong; covered with small scales,
singularly shaped, lanceolate, and hidden in the skin. The first dorsal
is formed by free spines in small numbers; the posterior rays of the
second dorsal and anal are detached finlets. Small teeth in the jaws,
on the vomer and palatine bones.

Twelve species are known from the Atlantic and Indo-Pacific; some enter
brackish water, whilst others are more numerous at some distance from
the shore. They attain to a length of from 2 to 4 feet. In the young,
which have been described as _Porthmeus_, the spines and finlets are
connected by membrane with the rest of the fin.

_Lichia_ is an allied genus from the Mediterranean, tropical Atlantic,
and the coast of Chili; five species.

   TEMNODON.--Body oblong, compressed, covered with cycloid scales
   of moderate size. Cleft of the mouth rather wide. Jaws with
   a series of strong teeth; smaller ones on the vomer and the
   palatine bones. The first dorsal with eight feeble spines
   connected by membrane; finlets none. Lateral line not shielded.
   The second dorsal and anal covered with very small scales.

_Temnodon saltator_, sometimes called “Skip-jack,” is spread over
nearly all the tropical and sub-tropical seas; it frequents principally
the coasts, but is also met with in the open sea. On the coasts of the
United States it is well known by the name of “Blue-fish,” being highly
esteemed as food, and furnishing excellent sport. It is one of the most
rapacious fishes, destroying an immense number of other shore-fishes,
and killing many more than they can devour. It grows to a length of 5
feet, but the majority of those brought to market are not half that
length.

   TRACHYNOTUS.--Body more or less elevated, compressed, covered
   with very small scales. Cleft of the mouth rather small, with
   short convex snout. Opercles entire. The first dorsal composed
   of free spines in small number. No finlets. Teeth always small,
   and generally lost with age.

Ten species are known from the tropical Atlantic and Indo-Pacific; they
rarely exceed a length of 20 inches. Some of the most common marine
fishes belong to this genus, for instance _T. ovatus_, which ranges
over the entire tropical zone.

PAMMELAS (_perciformis_) is allied to the preceding genus; from the
coast of New York.

  [Illustration: Fig. 198.--Magnified scale of Psettus argenteus.]

   PSETTUS.--Body much compressed and elevated; snout rather short.
   One dorsal, entirely covered with scales, with seven or eight
   spines; anal fin with three. Ventrals very small, rudimentary.
   Teeth villiform; no teeth on the palate. Scales small, ctenoid.

Only three species are known; one, _P. sebæ_, from the west coast of
Africa, the two others from the Indo-Pacific. _P. argenteus_ is a very
common fish, attaining to a length of about 10 inches.

  [Illustration: Fig. 199.--Psettus argenteus.]

   PLATAX.--Body much compressed and elevated; snout very short.
   One dorsal, with the spinous portion nearly entirely hidden, and
   formed by from three to seven spines; anal with three. Ventrals
   well developed, with one spine and five rays. Teeth setiform,
   with an outer series of rather larger teeth, notched at the top;
   palate toothless. Scales of moderate size or rather small.

These fishes are called “Sea-bats,” from the extraordinary length of
some portion of their dorsal and anal fins and of their ventrals. These
long lobes are generally of a deep black colour. In mature and old
individuals the fin-rays are much shorter than in the young, which have
been described as distinct species. There are probably not more than
seven species of “Sea-bats,” if so many, and they all belong to the
Indian Ocean and Western Pacific, where they are very common.

   ZANCLUS.--Body much compressed and elevated. One dorsal, with
   seven spines, the third of which is very elongate. No teeth on
   the palate. Scales minute, velvety.

One species (_Z. cornutus_), which is extremely common in the
Indo-Pacific. It is easily recognised by its snout, which is produced
like that of _Chelmon_, and by the broad black bands crossing the
yellow ground-colour. It attains to a length of eight inches, and
undergoes during growth similar changes as _Acanthurus_.

   ANOMALOPS.--Body oblong, covered with small, rough scales. Snout
   very short, convex, with wide cleft of the mouth. Eyes very
   large; below the eye, in a cavity of the infraorbital ring,
   there is a glandular phosphorescent organ. Villiform teeth in
   the jaws and on the palatine bones, none on the vomer. First
   dorsal fin short, with a few feeble spines connected by membrane.

This genus, of which one species only is known (_A. palpebratus_),
represents the family of Horse-Mackerels in the depths of the sea; but
we do not know, at present, at what depth it lives. Only six specimens
have been obtained hitherto from the vicinity of Amboyna, the Fidji,
and Paumotu Islands; the largest was twelve inches long.

   CAPROS.--Body compressed and elevated. Mouth very protractile.
   Scales rather small, spiny. First dorsal with nine spines, anal
   with three. Ventral fins well developed. Minute teeth in the
   jaws and on the vomer; none on the palatine bones.

The “Boar-fish” (_C. aper_) is common in the Mediterranean, and not
rarely found on the south coast of England.

Allied are _Antigonia_ and _Diretmus_, known from a few individuals
obtained at Madeira and Barbadoes; they are probably fishes which but
rarely come to the surface.

   EQUULA.--Body more or less compressed, elevated or oblong,
   covered with small, deciduous, cycloid scales. Mouth very
   protractile. Minute teeth in the jaws; none on the palate. One
   dorsal. Formula of the fins: D. 8/1516, A. 3/14, V. 1/5. The
   lower præopercular margin serrated.

  [Illustration: Fig. 200.--Equula edentula.]

Small species, abundant in the Indo-Pacific, disappearing on the coasts
of Japan and Australia. Some eighteen species have been described.

_Gazza_ is very similar to _Equula_, but armed with canine teeth in the
jaws.

Other genera referred to this family are _Lactarius_ (_L. delicatulus_,
common, and eaten on the East Indian coasts), _Seriolella_, _Paropsis_,
and _Platystethus_.


                        THIRD FAMILY--CYTTIDÆ.

_Body elevated, compressed, covered with small scales, or with
bucklers, or naked; eye lateral. Teeth conical, small. No bony stay
for the præoperculum. Dorsal fin composed of two distinct portions.
Ventrals thoracic. No prominent papilla near the vent. Gill-opening
wide. More than ten abdominal and more than fourteen caudal
vertebræ._

The fishes of the “Dory” family are truly marine, and inhabit the
temperate zone of the Northern and Southern Hemispheres. Some fossils
from tertiary formations (one from Licata) belong to the genus Zeus.

   ZEUS.--A series of bony plates runs along the base of the dorsal
   and anal fins; another series on the abdomen. Three or four anal
   spines.

“John Dorys” are found in the Mediterranean, on the eastern temperate
shores of the Atlantic, on the coasts of Japan and Australia. Six
species are known, all of which are highly esteemed for the table. The
English name given to one of the European species (_Zeus faber_) seems
to be partly a corruption of the Gascon “Jau,” which signifies cock,
“Dory” being derived from the French Dorée, so that the entire name
means Gilt-Cock. Indeed, in some other localities of Southern Europe it
bears the name of _Gallo_. The same species occurs also on the coasts
of South Australia and New Zealand. The fishermen of Roman Catholic
countries hold this fish in special respect, as they recognise in a
black round spot on its side the mark left by the thumb of St. Peter
when he took the piece of money from its mouth.

  [Illustration: Fig. 201.--Cyttus australis.]

   CYTTUS.--Body covered with very small scales; no osseous
   bucklers on any part of the body. Two anal spines; ventral fins
   composed of one spine and six or eight rays.

Three species are known from Madeira, South Australia, and New Zealand.


                      FOURTH FAMILY--STROMATEIDÆ.

_Body more or less oblong and compressed, covered with very small
scales; eye lateral. Dentition very feeble; œsophagus armed with
numerous horny, barbed processes. No bony stay for the præoperculum.
Dorsal fin single, long, without distinct spinous division. More than
ten abdominal and more than fourteen caudal vertebræ._

This small family consists of strictly marine and partly pelagic
species referred to two genera, _Stromateus_ and _Centrolophus_.
The former lacks ventral fins, at least in the adult stage, and is
represented by about ten species in almost all the tropical and warmer
seas. _Centrolophus_, hitherto known from two or three European species
only (of which one occasionally reaches the south coast of England,
where it is named “Black-fish”), has recently been discovered on the
coast of Peru, and has probably a much wider range.


                      FIFTH FAMILY--CORYPHÆNIDÆ.

_Body compressed; eye lateral. Teeth small, conical, if present;
œsophagus smooth. No bony stay for the præoperculum. Dorsal fin single,
long, without distinct spinous division. More than ten abdominal and
more than fourteen caudal vertebræ._

All the members of this family have pelagic habits. Representatives of
it have been recognized in some fossil remains: thus _Goniognathus_
from the Isle of Sheppey, and the living genus _Mene_ (_Gastrocnemus_)
at Monte Bolca.

   CORYPHÆNA.--Body compressed, rather elongate; adult specimens
   with a high crest on the top of the head; cleft of the mouth
   wide. A single dorsal extending from the occiput almost to the
   caudal, which is deeply forked; no distinct dorsal and anal
   spines. The ventrals are well developed, and can be received
   in a groove on the abdomen. Scales very small. Rasp-like teeth
   in the jaws, on the vomer and the palatine bones. Air-bladder
   absent.

  [Illustration: Fig. 202.--Dolphin from the Atlantic.]

Generally, though by misapplication of the name, called “Dolphins.”
About six species are known, each of which is probably distributed
over all the tropical and sub-tropical seas. Strictly pelagic in their
habits, they are most powerful swimmers; they congregate in shoals,
and pursue unceasingly the Flying-Fish, which try to escape their
enemies by long flying leaps. They attain to a length of six feet,
and are eagerly caught by sailors on account of their well-flavoured
flesh. The beauty of their, unfortunately fugitive, colours has ever
been a subject of admiration. As far as the colours are capable of
description, those of the common species (_C. hippurus_), which is
often seen in the Mediterranean, are silvery blue above, with markings
of a deeper azure, and reflections of pure gold, the lower parts being
lemon-yellow, marked with pale blue. The pectoral fins are partly lead
colour, partly yellow; the anal is yellow, the iris of the eye golden.
These iridescent colours change rapidly whilst the fish is dying, as in
the Mackerel. The form of the body, and especially of the head, changes
considerably with age. Very young specimens, from one to six inches
in length, are abundant in the open sea, and frequently obtained in
the tow-net. Their body is cylindrical, their head as broad as high,
and the eye relatively very large, much longer than the snout. As the
fish grows the body is more compressed, and finally a high crest is
developed on the head, and the anterior part of the dorsal fin attains
a height equal to that of the body.

   BRAMA.--Body compressed, and more or less elevated, covered with
   rather small scales; cleft of the mouth very oblique, with the
   lower jaw longest. Dorsal and anal fins many-rayed, the former
   with three or four, the latter with two or three, spines; caudal
   deeply forked. Ventrals thoracic, with one spine and five rays.
   The jaws with an outer series of stronger teeth.

Pelagic fishes which, like the allied genus _Taractes_, range over
almost all the tropical and temperate seas.

   LAMPRIS.--Body compressed and elevated, covered with very small
   deciduous scales; cleft of the mouth narrow. A single dorsal,
   without a spinous portion. Ventrals composed of numerous rays.
   Teeth none.

  [Illustration: Fig. 203.--Lampris luna.]

The “Sun-fish” (_L. luna_) is one of the most beautiful fishes of
the Atlantic. It attains to the large size of four feet in length, is
bluish on the back, with round silvery spots, which colour prevails
on the lower parts; the fins are of a deep scarlet. It is said to be
excellent eating. It is a pelagic fish, not rare about Madeira, but
extending far northwards in the Atlantic; it seems to be rarer in the
Mediterranean. All the specimens hitherto obtained were full-grown
or nearly so. The skeleton exhibits several peculiarities, viz. an
extraordinary development and dilatation of the humeral arch, and great
strength of the numerous and closely-set ribs.

Other Coryphænoid genera are _Pteraclis_, _Schedophilus_, _Diana_,
_Ausonia_, and _Mene_; all pelagic forms.


                        SIXTH FAMILY--NOMEIDÆ.

_Body oblong, more or less compressed, covered with cycloid scales of
moderate size; eye lateral. No bony stay for the præoperculum. Dorsal
fin with a distinct spinous portion separated from the soft; sometimes
finlets; caudal forked. More than ten abdominal, and more than fourteen
caudal vertebræ._

Marine fishes; pelagic, at least when young.

  [Illustration: Fig. 204.--Gastrochisma melampus.]

   GASTROCHISMA.--Cleft of the mouth wide. Finlets behind the
   dorsal and anal fins. The ventral fins are exceedingly broad
   and long, and can be completely concealed in a fold of the
   abdomen.

_G. melampus_, from the coast of New Zealand; scarce.

   NOMEUS.--Cleft of the mouth narrow. No finlets. The ventral fin
   is long and broad, attached to the abdomen by a membrane, and
   can be received in a fissure of the abdomen.

_N. gronovii_ is a common pelagic fish in the Atlantic and Indian
Oceans; of small size.

Other genera belonging to this family are _Psenes_ and _Cubiceps_.


                      SEVENTH FAMILY--SCOMBRIDÆ.

_Body oblong, scarcely compressed, naked or covered with small
scales; eye lateral. Dentition well developed. No bony stay for the
præoperculum. Two dorsal fins; generally finlets. Ventrals thoracic,
with one spine and five rays. More than ten abdominal, and more than
fourteen caudal vertebræ._

The fishes of the “Mackerel” family are pelagic forms, abundant in all
the seas of the tropical and temperate zones. They are one of the four
families of fishes which are the most useful to man, the others being
the Gadoids, Clupeoids, and Salmonoids. They are fishes of prey, and
unceasingly active, their power of endurance in swimming being equal
to the rapidity of their motions. Their muscles receive a greater
supply of blood-vessels and nerves than in other fishes, and are of a
red colour, and more like those of birds or mammals. This energy of
muscular action causes the temperature of their blood to be several
degrees higher than in other fishes. They wander about in shoals, spawn
in the open sea, but periodically approach the shore, probably in the
pursuit of other fishes on which they feed.[43]

_Scombridæ_ are well represented in tertiary formations: in the Eocene
schists of Glaris two extinct genera, _Palimphyes_ and _Isurus_, have
been discovered. In Eocene and Miocene formations _Scomber_, _Thynnus_,
and _Cybium_ are not uncommon.

   SCOMBER.--The first dorsal continuous, with feeble spines; five
   or six finlets behind the dorsal and anal. Scales very small,
   and equally covering the whole body. Teeth small. Two short
   ridges on each side of the caudal fin.

Mackerels proper are found in almost all temperate and tropical seas,
with the exception of the Atlantic shores of temperate South America,
where they have not been found hitherto. In Europe, and probably
also on the coast of England, three species occur: _S. scomber_, the
common Mackerel, which lacks an air-bladder; _S. pneumatophorus_, a
more southern species, with an air-bladder; and _S. colias_, like the
former, but with a somewhat different coloration, and often called
“Spanish” Mackerel. On the Cape of Good Hope, in Japan, on the coast
of California, in South Australia, and New Zealand, Mackerels are
abundant, which are either identical with, or very closely allied
to, the European species. On the coasts of the United States the
same species occur which tenant the western parts of the Atlantic.
Altogether seven species are known.

  [Illustration: Fig. 205.--Thynnus thynnus.]

   THYNNUS.--The first dorsal continuous, with the spines rather
   feeble; from six to nine finlets behind the dorsal and anal.
   Scales of the pectoral region crowded, forming a corslet. Teeth
   rather small. A longitudinal keel on each side of the tail.

The best-known species of this genus is the “Tunny” (_Thynnus
thynnus_), abundant in the Mediterranean, and ranging to the south
coast of England and to Tasmania. It is one of the largest fishes of
the ocean, attaining to a length of 10 feet, and to a weight of more
than 1000 lbs. The fishery of the Tunny is systematically carried on in
the Mediterranean, and dates from the most remote antiquity. Its salted
preparation was esteemed by the Romans under the name of _Saltamentum
sardicum_. Its flesh is extensively eaten now, fresh as well as
preserved.

_Thynnus pelamys_, or the “Bonito,” is equally well known, and ranges
over all the tropical and temperate seas; it eagerly pursues the
Flying-fish, and affords welcome sport and food to the sailor. In its
form it resembles the Tunny, but is more slender and rarely above three
feet long.

Some of the other species are provided with very long pectoral fins,
and generally called by sailors “Albacore.” They are said to grow to a
length of six feet; Bennett in his “Whaling Voyage,” vol. ii. p. 278,
makes the following observations on _Th. germo_, from the Pacific:
“Ships when cruising slowly in the Pacific Ocean, are usually attended
by myriads of this fish for many successive months. A few days’ rapid
sailing is, nevertheless, sufficient to get rid of them, however
numerous they may be, for they seldom pay more than very transient
visits to vessels making a quick passage. When the ship is sailing with
a fresh breeze they swim pertinaciously by her side and take the hook
greedily, but should she be lying motionless or becalmed they go off
to some distance in search of prey, and cannot be prevailed upon to
take the most tempting bait the sailor can devise. It is probably as a
protection from their chief enemy, the Sword-fish, that they seek the
society of a ship. I am not aware that the Shark is also their enemy;
but they seemed to have an instinctive dread of this large fish, and
when it approached the ship, would follow it in shoals, and annoy it in
the same manner as the smaller birds may be seen to annoy those of a
larger and predaceous kind, as the hawk or owl. They are very voracious
and miscellaneous feeders. Flying-fish, Calmars, and small shoal-fish
are their most natural food; though they do not refuse the animal
offal from a ship. Amongst the other food contained in their maw, we
have found small Ostracions, File-fish, Sucking-fish, Janthina shells,
and pelagic crabs; in one instance a small Bonita, and in a second a
Dolphin eight inches long, and a Paper-nautilus shell containing its
sepia-tenant. It was often amusing to watch an Albacore pursuing a
Flying-fish, and to mark the precision with which it swam beneath the
feeble æronaut, keeping him steadily in view, and preparing to seize
him at the moment of his descent. But this the Flying-fish would often
elude by instantaneously renewing his leap, and not unfrequently escape
by extreme agility.”

   PELAMYS.--The first dorsal continuous, with the spines rather
   feeble; from seven to nine finlets behind the dorsal and
   anal. Scales of the pectoral region forming a corslet. Teeth
   moderately strong. A longitudinal keel on each side of the tail.

Five species are known, of which _P. sarda_ is common in the Atlantic
and Mediterranean.

   AUXIS.--Differing from the preceding two genera in having very
   small teeth in the jaws only, none on the palate.

_Auxis rochei_ common in the Atlantic, Mediterranean, and Indian
Ocean.

   CYBIUM.--The first dorsal continuous, with the spines rather
   feeble; generally more than seven finlets behind the dorsal and
   anal. Scales rudimentary or absent. Teeth strong; a longitudinal
   keel on each side of the tail.

Twelve species from the tropical Atlantic and Indian Ocean;
frequenting more the coast-region than the open sea; attaining to a
length of four or five feet.

   ELACATE.--Body covered with very small scales; head depressed;
   cleft of the mouth moderately wide; no keel on the tail. The
   spinous dorsal is formed by eight small free spines; finlets
   none. Villiform teeth in the jaws, on the vomer and the palatine
   bones.

_Elacate nigra_, a coast fish common in the warmer parts of the
Atlantic and the Indian Ocean.

   ECHENEIS.--The spinous dorsal fin is modified into an adhesive
   disk, occupying the upper side of the head and neck.

This genus is closely allied to the preceding, from which it differs
only by the transformation of the spinous dorsal fin into a sucking
organ. The spines being composed of two halves, each half is bent down
towards the right and the left, forming a support to a double series of
transverse lamellæ, rough on their edges, the whole disk being of an
oval shape and surrounded by a membranous fringe. Each pair of lamellæ
is formed out of one spine, which, as usual, is supported at the base
by an interneural spine. By means of this disk the “Sucking-fishes”
or “Suckers” are enabled to attach themselves to any flat surface,
a series of vacuums being created by the erection of the usually
recumbent lamellæ. The adhesion is so strong that the fish can only be
dislodged with difficulty, unless it is pushed forward by a sliding
motion. The Suckers attach themselves to sharks, turtles, ships, or any
other object which serves their purpose. They cannot be regarded as
parasites, inasmuch as they obtain their food independently of their
host. Being bad swimmers they allow themselves to be carried about by
other animals or vessels endowed with a greater power of locomotion.
They were as well known to the ancients as they are to the modern
navigators. Aristotle and Aelian mention the Sucker under the name of
φθεὶρ, or the _Louse_; “In the sea between Cyrene and Egypt there is a
fish about the Dolphin (_Delphinus_), which they call the Louse; this
becomes the fattest of all fishes, because it partakes of the plentiful
supply of food captured by the Dolphin.” Later writers, then, repeat
a story, the source of which is unknown, viz. that the “Remora” is
able to arrest vessels in their course, a story which has been handed
down to our own time. It need not be stated that this is an invention,
though it cannot be denied that the attachment of one of the larger
species may retard the progress of a sailing vessel, especially when,
as is sometimes the case, several individuals accompany the same ship.
An account of a somewhat ingenious way of catching sleeping turtles by
means of a Sucking-fish held by a ring fastened round its tail, appears
to have originated rather from an experiment than from regular practice.

Ten different species are known, of which _Echeneis remora_ and
_Echeneis naucrates_ are the most common. The former is short and grows
to a length of eight inches only, the latter is a slender fish, not
rarely found three feet long. The bulkiest is _Echeneis scutata_, which
attains to a length of two feet; individuals of that size weighing
about eight lbs.

The number of pairs of lamellæ varies in the various species, from 12
to 27. The caudal fin of some of the species undergoes great changes
with age. In young specimens the middle portion of the fin is produced
into a long filiform lobe. This lobe becomes gradually shorter, and the
fin shows a rounded margin in individuals of middle age. When the fish
approaches the mature state, the upper and lower lobes are produced,
and the fin becomes subcrescentic or forked.

   [See Günther, “On the History of Echeneis.” Ann. and Mag. Nat.
   Hist., 1860.]


                      EIGHTH FAMILY.--TRACHINIDÆ.

_Body elongate, low, naked or covered with scales. Teeth small,
conical. No bony stay for the præoperculum. One or two dorsal fins,
the spinous portion being always shorter and much less developed than
the soft; the anal similarly developed as the soft dorsal; no finlets.
Ventrals with one spine and five rays. Gill-opening more or less
wide. Ten or more than ten abdominal, and more than fourteen caudal
vertebræ._

Carnivorous coast-fishes of small size, found in every quarter of the
globe, but scarcely represented in the Arctic zone (_Trichodon_); on
the other hand, they are rather numerous towards the Antarctic circle.
All are bad swimmers, generally moving along the bottom in small
depths. Only one genus (_Bathydraco_) is known from the deep-sea.

A genus which shows the principal characters of this family
(_Callipteryx_), has been found in the tertiary deposits of Monte
Bolca; it is scaleless. A second genus, _Trachinopsis_, has been
recently described by Sauvage from the Upper Tertiary of Lorca in
Spain; and a third (_Pseudoeleginus_) from the Miocene of Licata.

This family may be subdivided into five groups:--

   1. In the URANOSCOPINA the eyes are on the upper surface of the
   head, directed upwards; the lateral line is continuous.

   URANOSCOPUS.--Head large, broad, thick, partly covered with bony
   plates; cleft of the mouth vertical. Scales very small. Two
   dorsal fins, the first with from three to five spines; ventrals
   jugular; pectoral rays branched. Villiform teeth in the jaws,
   on the vomer and palatine bones; no canines. Generally a long
   filament below and before the tongue. Gill-cover armed.

The position of the eyes on the upper surface of the head, which these
fishes have in common with many others, is well expressed by the name
_Uranoscopus_ (Stare-gazer). Their eyes are very small, and can be
raised or depressed at the will of the fish. They are inactive fishes,
generally lying hidden at the bottom between stones, watching for their
prey. The delicate filament attached to the bottom of their mouth, and
playing in front of it in the current of water which passes through the
mouth, serves to lure small animals within reach of the fish. Eleven
species are known from the Indo-Pacific and Atlantic, and one (_U.
scaber_) from the Mediterranean; they attain rarely a length of twelve
inches.

   LEPTOSCOPUS.--Form of the head as in _Uranoscopus_, but entirely
   covered with a thin skin. Scales small, cycloid. One continuous
   dorsal; ventrals jugular; pectoral rays branched. Villiform
   teeth in both jaws, on the vomer and palatine bones; canines
   none. No oral filament. Gill-cover unarmed.

  [Illustration: Fig. 206.--Leptoscopus macropygus.]

_Leptoscopus macropygus_, not rare on the coast of New Zealand.

Other genera of Stare-gazers are _Agnus_ from the Atlantic coasts of
North America; _Anema_ from the Indian Ocean and New Zealand; and
_Kathetostoma_ from Australia and New Zealand.

   2. In the TRACHININA the eyes are more or less lateral; the
   lateral line is continuous; and the intermaxillary without a
   larger tooth on its posterior portion.

   TRACHINUS.--Cleft of the mouth very oblique; eye lateral, but
   directed upwards. Scales very small, cycloid. Two dorsal fins,
   the first short, with six or seven spines; ventrals jugular; the
   lower pectoral rays simple. Villiform teeth in the jaws, on the
   vomer and palatine bones. Præorbital and præoperculum armed.

The “Weevers” are common fishes on the European coasts, and but too
well known to all fishermen; singularly enough they do not extend
across the Atlantic to the American coast, but reappear on the coast of
Chili! Wounds by their dorsal and opercular spines are much dreaded,
being extremely painful, and sometimes causing violent inflammation
of the wounded part. No special poison-organ has been found in these
fishes, but there is no doubt that the mucous secretion in the vicinity
of the spines has poisonous properties. The dorsal spines as well as
the opercular spine have a deep double groove in which the poisonous
fluid is lodged, and by which it is inoculated in the punctured wound.
On the British coasts two species occur, _T. draco_, the Greater
Weever, attaining to a length of twelve inches, and _T. vipera_, the
Lesser Weever, which grows only to half that size.

   CHAMPSODON.--Body covered with minute granular scales; lateral
   lines two, with numerous vertical branches. Cleft of the mouth
   wide, oblique. Eye lateral, but directed upwards. Two dorsal
   fins; ventral fins jugular; pectoral rays branched. Teeth in the
   jaws in a single series, thin, long, of unequal size. Teeth on
   the vomer, none on the palate. Gill-openings exceedingly wide.
   Præoperculum with a spine at the angle and a fine serrature on
   the posterior margin.

_Champsodon vorax_ is not uncommon at small depths off the
Philippine Islands, Admiralty Islands, and in the Arafura Sea.

   PERCIS.--Body cylindrical, with small ctenoid scales; cleft of
   the mouth slightly oblique; eye lateral, but directed upwards.
   Dorsal fins more or less continuous, the spinous with four or
   five short stiff spines; ventrals a little before the pectorals.
   Villiform teeth in the jaws, with the addition of canines; teeth
   on the vomer, none on the palatines. Opercles feebly armed.

Fifteen species; small, but prettily coloured shore-fishes of the
Indo-Pacific.

   SILLAGO.--Body covered with rather small, ctenoid scales.
   Cleft of the mouth small, with the upper jaw rather longer;
   eye lateral, large. Two dorsals, the first with from nine
   to twelve spines; ventrals thoracic. Villiform teeth in the
   jaws, and on the vomer, none on the palatine bones. Operculum
   unarmed; præoperculum serrated. The bones of the head with wide
   muciferous channels.

Eight species; small, plain-coloured shore-fishes, common in the Indian
Ocean to the coasts of Australia.

   BOVICHTHYS.--Head broad and thick; cleft of the mouth
   horizontal, with the upper jaw rather longer; eye lateral, more
   or less directed upwards. Scales none. Two separate dorsal
   fins, the first with eight spines; ventrals jugular; the lower
   pectoral rays simple. Villiform teeth in the jaws, on the vomer
   and the palatine bones; no canines. Operculum with a strong
   spine; præorbital and præoperculum not armed.

Three species are known from the South Pacific.

  [Illustration: Fig. 207.--Head of Bovichthys variegatus, from New
  Zealand.]

   BATHYDRACO.--Body elongate, sub-cylindrical; head depressed,
   with the snout much elongate, spatulate; mouth wide, horizontal,
   with the lower jaw prominent; eyes very large, lateral, close
   together. Scales very small, imbedded in the skin. Lateral line
   wide, continuous. One dorsal fin; ventrals jugular; the lower
   pectoral rays branched. Teeth in the jaws in villiform bands;
   none on the vomer or the palatine bones. Opercles unarmed; ten
   branchiostegals; the gill-membranes free from the isthmus, and
   but slightly united in front. Air-bladder none.

A deep-sea fish, found at a depth of 1260 fathoms in the Antarctic
Ocean (south of Heard Island).

   CHÆNICHTHYS.--Head very large, with the snout spatulate, and
   with the cleft of the mouth very wide. Eye lateral. Scales none;
   lateral line sometimes with granulated scutes. Two dorsals, the
   first with seven spines; ventrals jugular. Jaws with rasp-like
   teeth; palate toothless.

_Chænichthys rhinoceratus_ from Kerguelen’s Land (see Fig. 108, p.
291); and _Ch. esox_ from the Straits of Magelhaen.

Other genera belonging to this group are _Aphritis_, _Acanthaphritis_,
_Eleginus_, _Chænichthys_, and _Chimarrhichthys_ from the South Pacific
and Antarctic zone; _Cottoperca_ from the west coast of Patagonia;
_Percophis_ from the coast of Southern Brazil; and _Trichodon_ from the
coast of Kamtschatka.

   3. In the PINGUIPEDINA the body is covered with small scales;
   the eye lateral; the lateral line continuous; and the
   intermaxillary is armed with a larger tooth on its posterior
   portion, as in many Labroids.

Two genera, _Pinguipes_ and _Latilus_, from various parts of tropical
and sub-tropical seas, belong to this group.

   4. In the PSEUDOCHROMIDES, the lateral line is interrupted or
   not continued to the caudal fin; they have one continuous dorsal
   only.

These fishes are inhabitants of coral reefs or coasts:
_Opisthognathus_, _Pseudochromis_, _Cichlops_, and _Pseudoplesiops_.

   5. In the NOTOTHENIINA the lateral line is interrupted;
   and the dorsal fin consists of two separate portions.

They (with others) represent in the Antarctic zone the Cottoids of
the Northern Hemisphere: they have the same habits as their northern
analogues. In _Notothenia_, which on the southern extremity of South
America, in New Zealand, Kerguelen’s Land, etc., is represented by
about twenty species, the body is covered with ctenoid scales, and the
bones of the head are unarmed; whilst _Harpagifer_, a small species
with a similar range as _Notothenia_, has the body naked, and the
operculum and sub-operculum armed with long and strong spines.


                      NINTH FAMILY--MALACANTHIDÆ.

_Body elongate, with very small scales; mouth with thick lips; a
strong tooth posteriorly on the intermaxillary. Dorsal and anal fins
very long, the former with a few simple rays anteriorly; ventrals
thoracic, with one spine and five rays. Gill-opening wide, with the
gill-membranes united below the throat. Ten abdominal and fourteen
caudal vertebræ._

One genus only, _Malacanthus_, with three species from tropical
seas.


                       TENTH FAMILY--BATRACHIDÆ.

_Head broad and thick; body elongate, compressed behind; skin naked
or with small scales. No bony stay for the præoperculum. Teeth conical,
small or of moderate size. The spinous dorsal consists of two or three
spines only; the soft and the anal long. Ventrals jugular, with two
soft rays; pectorals not pediculated. Gill-opening a more or less
vertical slit before the pectoral, rather narrow._

Carnivorous fishes, of small size, living on the bottom of the sea near
the coast in the tropical zone, some species advancing into the warmer
parts of the temperate zones.

   BATRACHUS.--The spinous dorsal is formed by three stout spines.
   Gill-covers armed with spines. Circumference of the mouth and
   other parts of the head frequently provided with small skinny
   tentacles.

Some of the fishes of this genus possess a subcutaneous spacious
cavity behind the base of the pectoral fin, the inside of which is
coated with a reticulated mucous membrane. It opens by a foramen in
the upper part of the axil.--This apparatus is the same which is found
in many Siluroid fishes, and which has been noticed above, p. 192.
There cannot be any doubt that it is a secretory organ, but whether
the secretion has any poisonous properties, as in the Siluroids, or
as in _Thalassophryne_, has not been determined. No instance of
poisonous wounds having been inflicted by these fishes is on record.
Twelve species are known, the distribution of which coincides with that
of the family; one very fine species, _B. didactylus_, occurs in
the Mediterranean.

   THALASSOPHRYNE.--The spinous dorsal is formed by two spines
   only, each of which is hollow, like the opercular spine, and
   conveys the contents of a poison-bag situated at its base.
   Canine teeth none.

  [Illustration: Fig. 208.--Thalassophryne reticulata.]

Two species are known from the Atlantic and Pacific coasts of Central
America. The poison-apparatus is more perfectly developed than any
other known at present in the class of fishes; it has been described
above, p. 192. The species figured, _Th. reticulata_, is not uncommon
at Panama, and attains to a length of fifteen inches.

   PORICHTHYS.--Two small dorsal spines; a canine tooth on each
   side of the vomer.

Two species, from the Atlantic and Pacific sides of Central and South
America.


                    ELEVENTH FAMILY--PSYCHROLUTIDÆ.

_Body rather elongate, naked; head broad. Spinous dorsal separate or
absent. Ventral fins close together, thoracic, composed of a few rays.
Teeth small. Three gills and a half; pseudobranchiæ well developed;
gill-openings of moderate width, the gill-membranes being attached to
the isthmus._

Of this family only two representatives are known, viz. _Psychrolutes
paradoxus_, from Vancouver’s Islands, without first dorsal fin; and
_Neophrynichthys latus_, from New Zealand, with two dorsal fins. Both
are very scarce marine fishes.


                      TWELFTH FAMILY--PEDICULATI.

_Head and anterior part of the body very large, without scales. No
bony stay for the præoperculum. Teeth villiform or rasp-like. The
spinous dorsal is advanced forwards, composed of a few more or less
isolated spines, often transformed into tentacles; or entirely absent.
Ventral fins jugular, with four or five soft rays, sometimes absent.
The carpal bones are prolonged, forming a sort of arm, terminating in
the pectoral. Gill-opening reduced to a small foramen, situated in or
near the axil. Gills two and a half, or three, or three and a half;
pseudobranchiæ generally absent._

This family contains a larger number of bizarre forms than any other;
and there is, perhaps, none in which the singular organisation of the
fish is more distinctly seen to be in consonance with its habits.
Pediculates are found in all seas. The habits of all are equally
sluggish and inactive; they are very bad swimmers; those found near the
coasts lie on the bottom of the sea, holding on with their arm-like
pectoral fins by seaweed or stones, between which they are hidden;
those of pelagic habits attach themselves to floating seaweed or
other objects, and are at the mercy of wind and current. A large
proportion of the genera, therefore, have gradually found their way to
the greatest depths of the ocean; retaining all the characteristics of
their surface-ancestors, but assuming the modifications by which they
are enabled to live in abyssal depths.

   LOPHIUS.--Head exceedingly large, broad, depressed, with the
   eyes on its upper surface; cleft of the mouth very wide. Jaws
   and palate armed with rasp-like depressible teeth of unequal
   size. Body naked; bones of the head armed with numerous spines.
   The three anterior dorsal spines are isolated, situated on the
   head, and modified into long tentacles; the three following
   spines form a continuous fin; the soft dorsal and anal short.
   Gills three. Young individuals have the tentacles beset with
   lappets, and most of the fin-rays prolonged into filaments.

These fishes are well known under the names “Fishing-Frog,”
“Frog-fishes,” “Anglers,” or “Sea-devils.” They are coast-fishes,
living at very small depths. Four species are known: the British
species (_L. piscatorius_) found all round the coasts of Europe
and Western North America, and on the Cape of Good Hope; a second
(Mediterranean) species, _L. budegassa_; _L. setigerus_ from China and
Japan; and _L. naresii_ from the Admiralty Islands.

  [Illustration: Fig. 209.--Lophius piscatorius.]

  [Illustration: Fig. 210.--A young Fishing-Frog.]

The habits of all these species are identical. The wide mouth
extends all round the anterior circumference of the head, and both
jaws are armed with bands of long pointed teeth, which are inclined
inwards, and can be depressed so as to offer no impediment to an
object gliding towards the stomach, but prevent its escape from the
mouth. The pectoral and ventral fins are so articulated as to perform
the functions of teeth, the fish being enabled to move, or rather to
walk, on the bottom of the sea, where it generally hides itself in
the sand, or amongst seaweed. All round its head, and also along the
body, the skin bears fringed appendages, resembling short fronds of
seaweed; a structure which, combined with the extraordinary faculty of
assimilating the colours of the body to its surroundings, assists this
fish greatly in concealing itself in places which it selects on account
of the abundance of prey. To render the organisation of these creatures
perfect in relation to their wants, they are provided with three long
filaments inserted along the middle of the head, which are, in fact,
the detached and modified three first spines of the anterior dorsal
fin. The filaments most important in the economy of the fishing-frogs
is the first, which is the longest, terminates in a lappet, and is
movable in every direction. There is no doubt that the Fishing-frog,
like many other fish provided with similar appendages, plays with this
filament as with a bait, attracting fishes, which, when sufficiently
near, are ingulfed by the simple act of the Fishing-frog opening its
gape. Its stomach is distensible in an extraordinary degree, and not
rarely fishes have been taken out of it quite as large and heavy as
their destroyer. The British species grows to a length of more than
five feet; specimens of three feet are common. Baird records that the
spawn of the same species has been observed as a floating sheet of
mucus, of from some 60 to 100 square feet.

   CERATIAS.--Head and body much compressed and elevated; cleft
   of the mouth wide, subvertical. Eyes very small. Teeth in the
   jaws rasp-like, depressible; palate toothless. Skin covered
   with numerous prickles. The spinous dorsal is reduced to two
   long isolated spines, the first on the middle of the head, the
   second on the back. The soft dorsal and anal short; caudal very
   long. Ventrals none; pectorals very short. Two and a half gills.
   Skeleton soft and fibrous.

_Ceratias holbölli_, a deep-sea fish; only a few examples have been
found near the coast of Greenland, and from the mid-Atlantic; the
latter at a depth of 2400 fathoms. Deep black.

   HIMANTOLOPHUS.--Head and body compressed and elevated; cleft
   of the mouth wide, oblique. Eyes very small. Teeth of the jaws
   rasp-like, depressible; palate toothless. Skin with scattered
   conical tubercles. The spinous dorsal is reduced to a single
   tentacle on the head. The soft dorsal, anal, caudal, and
   pectoral short. Ventrals none. Three and a half gills. Skeleton
   soft and fibrous.

This is another deep-sea form, hitherto found in very few examples in
the Arctic and Mid-Atlantic Oceans. The single tentacle is beset with
many long filaments at its extremity, thus answering the same purpose
which is attained by a greater number of tentacles. Deep black.

   MELANOCETUS.--Head and body compressed; head very large; cleft
   of the mouth exceedingly wide, vertical. Eyes very small. Teeth
   of the jaws and vomer rasp-like, depressible. Skin smooth. The
   spinous dorsal is reduced to a single filament placed on the
   head. The soft dorsal and anal short. Ventrals none.

  [Illustration: Fig. 211.--Melanocetus johnsonii.]

Two species are known from the Atlantic: _M. bispinossus_ and _M.
johnsonii_, obtained at depths of from 360 to 1800 fathoms. The
specimen figured was not quite four inches long, and contained in
its stomach, rolled up spirally into a ball, a Scopeline fish which
measured 7½ inches in length and one inch in depth.

   ONEIRODES.--A deep-sea fish from the Arctic Ocean, differing
   from the preceding in possessing a second isolated dorsal ray on
   the back.

   ANTENNARIUS.--Head very large, high, compressed; cleft of the
   mouth vertical or subvertical, of moderate width. Jaws and
   palate armed with rasp-like teeth. Eye small. Body naked or
   covered with minute spines; generally with tentacles. The
   spinous dorsal is reduced to three isolated spines, the anterior
   of which is modified into a tentacle, situated above the snout.
   The soft dorsal of moderate length; anal short. Ventrals present.

The fishes of this genus are pelagic, frequently met with in mid-ocean
between the tropics, especially in parts of the sea with floating
vegetation; not rarely individuals are found far from their native
latitudes, carried by currents to the coasts of Norway and New Zealand.
Their power of swimming is most imperfect. When near the coast they
conceal themselves between corals, stones, or fucus, holding on to the
ground by means of their arm-like pectoral fins. Their coloration is so
similar to their surroundings that it is hardly possible to distinguish
the fish from a stone or coral overgrown with vegetation. Their way of
attracting and seizing their prey is evidently the same as in the other
fishes of this family. The extraordinary range of some of the species
which inhabit the Atlantic as well as the Indo-Pacific Oceans, is the
consequence of their habit of attaching themselves to floating objects.
Almost all the species are highly coloured, but the pattern of the
various colours varies exceedingly. These fishes do not attain to any
considerable size, and probably never exceed a length of ten inches. A
great number of species have been distinguished by ichthyologists, but
probably not more than twenty are known at present. The species figured
on p. 295 (_A. caudomaculatus_) is common in the Red Sea, and
probably occurs in other parts of the Indian Ocean.

_Brachionichthys_ and _Saccarius_ are allied genera from South
Australia, Tasmania, and New Zealand.

   CHAUNAX.--Head very large, depressed; cleft of the mouth wide,
   subvertical; eye small; rasp-like teeth in the jaws and palate.
   Skin covered with minute spines. The spinous dorsal is reduced
   to a small tentacle above the snout; the soft dorsal of moderate
   length; anal short; ventrals present.

A deep-sea fish (_Ch. pictus_), of uniform pink colour; hitherto
found near Madeira and the Fidji Islands, at a depth of 215 fathoms.

   MALTHE.--Anterior portion of the body very broad and depressed.
   The anterior part of the snout is produced into a more or less
   prominent process, beneath which there is a tentacle retractile
   into a cavity. Jaws and palate with villiform teeth. Skin with
   numerous conical protuberances. Soft dorsal fin and anal very
   short. Gill-opening superiorly in the axil; gills two and a half.

Although the rostral tentacle is situated at the lower side of the
projection of the snout, it must be regarded as the homologue of
a dorsal spine. In some of the preceding genera, _Oneirodes_ and
_Chaunax_, the first dorsal spine is so far advanced on the snout as
to come into connection with the intermaxillary processes; and the
position of the rostral tentacle in _Malthe_ is only a still more
advanced step towards the same special purpose for which the first
dorsal spine is used in this family, viz. for the purpose of obtaining
food. In _Malthe_ it is obviously an organ of touch. This genus belongs
to the American shores of the Atlantic; _M. vespertilio_ being a
tropical, _M. cubifrons_ a northern species.

   HALIEUTÆA.--Head exceedingly large, depressed, nearly circular
   in its circumference. Cleft of the mouth wide, horizontal.
   Jaws with small rasp-like teeth; palate smooth. Forehead
   with a transverse bony bridge, beneath which is a tentacle
   (rostral spine) retractile into a cavity. Body and head covered
   with small stellate spines. Soft dorsal and anal very short.
   Gill-opening superiorly in the axil; gills two and a half.

A coast-fish (_H. stellata_) from China and Japan. Frequently found dry
in Chinese insect-boxes.

This genus appears to be represented in the Atlantic Ocean by
_Halieutichthys_ from Cuba, and by _Dibranchus_, dredged at a depth of
360 fathoms off the coast of West Africa; the latter genus possesses
two gills only. Another genus, covered with large scattered tubercles,
_Aegæonichthys_, has recently been described from New Zealand.


                      THIRTEENTH FAMILY--COTTIDÆ.

_Form of the body oblong, sub-cylindrical. Cleft of the mouth lateral.
Dentition feeble, generally in villiform bands. Some bones of the head
are armed; and a bony stay connects the præopercular spine with the
infraorbital ring. Two dorsal fins (rarely one), the spinous being less
developed than the soft and than the anal. Ventrals thoracic, with five
or less soft rays._

The fishes of this family are of small size, bad swimmers, and
generally living on the bottom, near the coasts, of almost all the
arctic, temperate, and tropical seas. Only a few live in fresh water.
They prefer shallow to deep water; and there is only one instance
known of a member of this family living at a great depth, viz. _Cottus
bathybius_ from the Japanese sea, which is stated to have been dredged
in a depth of 565 fathoms. Fossil representatives are few in number:
two or three species of _Trigla_; others, although having a general
resemblance to the genus _Cottus_, were covered with ctenoid scales,
and therefore are referred to a distinct genus, _Lepidocottus_; they
are from tertiary formations.

   COTTUS.--Head broad, depressed, rounded in front; body
   sub-cylindrical, compressed posteriorly. Scaleless; lateral line
   present. Pectoral rounded, with some or all the rays simple.
   Jaws and vomer with villiform teeth; palatine teeth none.

The “Bull-heads” or “Miller’s Thumbs” are small fishes from the
shores and fresh waters of the northern temperate zone. Some forty
species are known; the greater number live in the northern half of
the temperate zone. On the shore, as well as in rivers, they prefer
rocky or stony to muddy ground, lying concealed between the stones,
and watching for their prey, which consists of small crustaceans and
other aquatic animals. The common British Miller’s Thumb (_C. gobio_)
is found in almost all suitable fresh waters of Northern and Central
Europe, especially in small streams, and extends into Northern Asia.
Other freshwater species abound in North America and Northern Asia.
_Cottus scorpius_ and _C. bubalis_, the common European marine species,
range across the Atlantic to the American coasts. The male is said
to construct a nest, for the reception of the spawn, of seaweeds and
stones, and to anxiously watch and defend his offspring. The spine at
the angle of the præoperculum, which is simple in the majority of the
freshwater species, is frequently armed with accessory processes, and
antler-like, in marine.

   CANTRIDERMICHTHYS differs from _Cottus_ in having teeth on the
   palatine bones.

Eleven species are known, distributed like _Cottus_, but absent in
Europe and North-western Asia.

   ICELUS.--Head large, armed at the gill-covers and on the neck;
   body with a dorsal series of bony plates from the neck to
   the base of the caudal; lateral line with osseous tubercles;
   scattered scales on the sides and abdomen. Ventrals thoracic,
   with less than five rays. No pectoral filaments. Villiform teeth
   in the jaws, on the vomer and palatine bones.

Represents Cottus in the far north; _I. hamatus_ is common in
Spitzbergen and Greenland, and has been found in abundance in lat. 81°
44’.

   PLATYCEPHALUS.--Head broad, much depressed, more or less armed
   with spines; body depressed behind the head, sub-cylindrical
   towards the tail, covered with ctenoid scales. Two dorsal fins;
   the first spine isolated from the others. Ventrals thoracic,
   but rather remote from the base of the pectorals. Villiform
   teeth in the jaws, on the vomer and palatine bones.

  [Illustration: Fig. 212.--Platycephalus cirrhonasus, from Port
  Jackson.]

About forty species are known, of which some attain a length of two
feet. This genus represents in the tropical Indian Ocean the _Cotti_
of the Arctic, and the _Nototheniæ_ of the Antarctic zone. Like these,
they live on the bottom in shallow water, hidden in the sand, the
colours of which are assimilated by those of their body. Therefore,
they are very scarce near coral islands which are surrounded by great
depths; whilst the number of species is rather considerable on many
points of the shelving Australian coasts. Their long and strong ventral
fins are of great use to them in locomotion. _P. insidiator_ is one of
the most common Indian and Australian fishes, and readily recognised by
two oblique black bands on the upper and lower caudal lobes.

  [Illustration: Fig. 213.--Scale from the lateral line of the same
  fish.]

   HOPLICHTHYS, similar to _Platycephalus_, but with the back and
   sides of the body covered with bony spiny plates. No separate
   dorsal spine.

One species, _H. langsdorffii_, is common on the coast of Japan,
and frequently placed dry by the Chinese into their insect-boxes.

   TRIGLA.--Head parallelopiped, with the upper surface and the
   sides entirely bony, the enlarged infraorbital covering the
   cheek.

Two dorsal fins. Three free pectoral rays. Villiform teeth. Air-bladder
generally with lateral muscles, often divided into two lateral halves.
The species may be referred to three groups:--

   1. Palatine teeth none; scales exceedingly small, except those
   of the lateral line: _Trigla_.

   2. Palatine teeth none; scales of moderate size: _Lepidotrigla_.

   3. Palatine teeth present: _Prionotus_.

  [Illustration: Fig. 214.--Trigla pleuracanthica.]

  [Illustration: Fig. 215.--Scute of the lateral line of the same
  fish.]

About forty species of “Gurnards” are known from tropical and temperate
zones. They are too well known to need detailed description; one of
their principal characteristics is the three free finger-like pectoral
appendages, which serve as organs of locomotion as well as touch, and
which are supplied with strong nerves, as noticed above (pp. 108 and
120). The fins are frequently beautifully ornamented, especially the
inner side of the long and broad pectorals, which is most exposed to
the light when the fish is floating on the surface of the water, with
pectorals spread out like wings. The grunting noise made by Gurnards
when taken out of the water is caused by the escape of gas from the
air-bladder through the open pneumatic duct. Gurnards are generally
used as food; seven species occur on the British coast: the Red Gurnard
(_T. pini_), the Streaked Gurnard (_T. lineata_), the Sapphirine
Gurnard (_T. hirundo_), the Grey Gurnard (_T. gurnardus_), Bloch’s
Gurnard (_T. cuculus_), the Piper (_T. lyra_), and the Long-finned
Gurnard (_T. obscura_ or _T. lucerna_). Singularly, the European
species cross the Atlantic but rarely, the American species belonging
chiefly to the division _Prionotus_.

Several other genera belong to this family; for completeness’ sake they
are mentioned here, viz. _Bunocottus_ from Cape Horn; _Rhamphocottus_,
_Triglops_ from Arctic North America; _Podabrus_, _Blepsias_,
_Nautichthys_, _Scorpænichthys_, _Hemilepidotus_, _Artedius_, from the
North Pacific; _Ptyonotus_, from Lake Ontario; _Polycaulus_ from Indian
Seas; Bembras from the Japanese Sea.


                    FOURTEENTH FAMILY--CATAPHRACTI.

_Form of the body elongate, sub-cylindrical. Dentition feeble. Body
completely cuirassed with osseous keeled scales or plates. A bony stay
connects the angle of the præoperculum with the infraorbital ring.
Ventrals thoracic._

Marine fishes, and partly pelagic. _Petalopteryx_, from the chalk of
Mount Lebanon, is supposed to have a resemblance to _Dactylopterus_.

   AGONUS.--Head and body angular, covered with bony plates. Two
   dorsal fins; no pectoral appendages. Small teeth in the jaws.

Small fishes, from the northern parts of the temperate zone and
extending into the Arctic Ocean; the genus reappears in the Southern
Hemisphere on the coast of Chile. Of the eleven species known, one
(_A. cataphractus_) is not uncommon on the coast of Great Britain.

   ASPIDOPHOROIDES, from Greenland, has a very similar form of the
   body, but possesses one short dorsal fin only.

   SIPHAGONUS.--With the snout produced into a long tube like a
   Syngnathus; chin prominent, with a barbel.

From Behring’s Strait and Japan.

   PERISTETHUS.--Head parallelopiped, with the upper surface and
   the sides entirely bony; each præorbital prolonged into a long
   flat process, projecting beyond the snout. Body cuirassed with
   large bony plates. One continuous dorsal, or two dorsals, of
   which the second is the more developed. Two free pectoral
   appendages. Teeth none; lower jaw with barbels.

Singularly shaped fishes, of rather small size, from the Mediterranean,
the warmer parts of the Atlantic, and the Indian Ocean; of the ten
species known one species only has been found in the Pacific, near the
Sandwich Islands. The European species is _P. cataphractum_. They are
not common, and probably inhabit greater depths than the Gurnards, with
which they have much in common as regards their habits.

  [Illustration: Fig. 216.--Dactylopterus volitans.]

   DACTYLOPTERUS.--Head parallelopiped, with the upper surface and
   the sides entirely bony; scapula and angle of the præoperculum
   produced into long spines. Body with strongly keeled scales of
   moderate size; lateral line none. Two dorsal fins, the second
   not much longer than the first; pectoral very long, an organ of
   flying, with the upper portion detached and shorter. Granular
   teeth in the jaws; none on the palate. Air-bladder divided into
   two lateral halves, each with a larger muscle.

Of “Flying Gurnards” three species only are known, which are very
abundant in the Mediterranean, the tropical Atlantic, and Indo-Pacific.
They, and the Flying Herrings (Exocoetus), are the only fishes which
are enabled by their long pectoral fins to take flying leaps out of the
water, and deserve the name of “Flying-Fishes.” They are much heavier,
and attain to a larger size, than the Exocoeti, specimens of eighteen
inches in length not being scarce. When young, their pectorals are much
shorter, and, consequently, they are unable to raise themselves out of
the water (_Cephalacanthus_).

The vertebral column shows a singular coalescence of the anterior
vertebræ, which form a simple tube, as in _Fistularia_.

       *       *       *       *       *

WE insert here as an appendix to this division the small family of
_Pegasidæ_, the natural affinities of which are not yet clearly
understood, but which resembles in some of its characters the
_Cataphracti_.


                      FIFTEENTH FAMILY--PEGASIDÆ.

_Body entirely covered with bony plates, anchylosed on the trunk
and movable on the tail. Barbels none. The margin of the upper jaw is
formed by the intermaxillaries and their cutaneous prolongation, which
extends downwards to the extremity of the maxillaries. Gill-cover
formed by a large plate, homologous to the operculum, præoperculum,
and sub-operculum; interoperculum a long fine bone, hidden below the
gill-plate. One rudimentary branchiostegal. The gill-plate is united
with the isthmus by a narrow membrane; gill-openings narrow, in front
of the base of the pectoral fin. Gills four, lamellated. Pseudobranchiæ
and air-bladder absent. One short dorsal and anal fin, opposite to each
other. Ventral fin present. Ovarian sacs closed._

One genus only is known, _Pegasus_. Its pectoral fins are broad,
horizontal, long, composed of simple rays, some of which are sometimes
spinous. Ventral fins one- or two-rayed. Upper part of the snout
produced into a shorter or longer process. Mouth inferior, toothless.
Suborbital ring well developed, forming a suture with the gill-cover.
Vertebræ in small number, thin; no ribs. Four species are known, two
of which are of a shorter, and the two others of a longer form. The
former are _P. draconis_, common in the Indian Ocean, and _P. volans_,
which is frequently stuck by the Chinese into the insect-boxes which
they manufacture for sale. The two elongate species, _P. natans_ and
_P. lancifer_, are from the Chinese and Australian coasts. They are all
very small fishes, probably living on sandy shoal places near the coast.

  [Illustration: Fig. 217.--Pegasus natans.]


             NINTH DIVISION--ACANTHOPTERYGII GOBIIFORMES.

_The spinous dorsal, or spinous portion of the dorsal is always
present, short, either composed of flexible spines, or much less
developed than the soft; the soft dorsal and anal of equal extent.
No bony stay for the angle of the præoperculum. Ventrals thoracic or
jugular, if present, composed of one spine and five, rarely four, soft
rays. A prominent anal papilla._

Shore-fishes, mostly exclusively marine, but some entering and living
in fresh waters.


                       FIRST FAMILY--DISCOBOLI.

_Body thick or oblong, naked or tubercular. Teeth small. Ventral
fins with one spine and five rays, all being rudimentary and forming
the osseous support of a round disk, which is surrounded by a cutaneous
fringe. Gill-openings narrow, the gill-membranes being attached to the
isthmus._

Carnivorous fishes, living at the bottom of the shores of northern
seas. By their ventral disk they are enabled to attach themselves very
firmly to rocks.

   CYCLOPTERUS.--Body thick, short, covered with a viscous,
   tubercular skin. Head large, snout short. Villiform teeth in the
   jaws, none on the palate. Skeleton soft, with but little earthy
   matter.

  [Illustration: Fig. 218.--Cyclopterus lumpus. _a_, Ventral
  disk.]

Three species of “Lump-suckers” are known from the northern temperate
and the arctic zones. The common North European and North American
species, _C. lumpus_, is known also by the names of “Cock- and
Hen-Paddle.” It attains to a length of twenty-four inches, but
generally is much smaller. It is difficult to remove it from any object
to which it once has attached itself by means of its sucking-disk. Its
skin is so thick as to more or less entirely conceal the first dorsal
fin; it is covered with rough tubercles, the larger ones being arranged
in four series along each side of the body. In young specimens these
tubercles are absent. The arctic species, _C. spinosus_, has large
conical plates on the head and body, each plate with a spine in the
centre. Also of this species the young are naked, the plates making
only gradually their appearance, in the form of groups of tubercles.
Their development is irregular, as young specimens of the same size may
be entirely naked or tubercular. This species ranges beyond the 81°
lat. N.

  [Illustration: Fig. 219.--Young of Cyclopterus spinosus, from the
  Arctic Ocean, natural size.]

   LIPARIS.--Body sub-cylindrical, enveloped in a more or less
   loose naked skin; head broad, obtuse. The infraorbital bone is
   styliform posteriorly, extending backwards to the margin of
   the præoperculum. One dorsal fin, with feeble flexible rays.
   Villiform teeth in the jaws, none on the palate.

Small fishes from the northern coasts of the temperate zone, ranging
beyond the arctic circle. Eight species are known, of which two (_L.
lineatus_ and _L. montagui_) occur on the British coasts.


                        SECOND FAMILY--GOBIIDÆ.

_Body elongate, naked or scaly. Teeth generally small, sometimes
with canines. The spinous dorsal fin, or portion of the dorsal fin, is
the less developed, and composed of flexible spines; anal similarly
developed as the soft dorsal. Sometimes the ventrals are united into
a disk. Gill-opening more or less narrow, the gill-membranes being
attached to the isthmus._

Small carnivorous littoral fishes, many of which have become
acclimatised in fresh water. They are very abundant with regard to
species as well as individuals, and found on or near the coasts of all
temperate and tropical regions. Geologically they appear first in the
chalk.

   GOBIUS.--Body scaly. Two dorsal fins, the anterior generally
   with six flexible spines. Ventral fins united, forming a disk
   which is not attached to the abdomen. Gill-opening vertical,
   moderately wide.

  [Illustration: Fig. 220.--Gobius lentiginosus, from New Zealand.]

The “Gobies” are distributed over all temperate and tropical coasts,
and abundant, especially on the latter. Nearly three hundred species
have been described. They live especially on rocky coasts, attaching
themselves firmly with their ventrals to a rock in almost any position,
and thus withstanding the force of the waves. Many of the species seem
to delight in darting from place to place in the rush of water which
breaks upon the shore. Others live in quiet brackish water, and not
a few have become entirely acclimatised in fresh water, especially
lakes. The males of some species construct nests for the eggs, which
they jealously watch, and defend even for some time after the young are
hatched. Several species are found on the British coast: _G. niger_,
_paganellus_, _auratus_, _minutus_, _ruthensparri_. Fossil species of
this genus have been found at Monte Bolca.

A very small Goby, _Latrunculus pellucidus_, common in some localities
of the British Islands and other parts of Europe, is distinguished by
its transparent body, wide mouth, and uniserial dentition. According
to R. Collett it offers some very remarkable peculiarities. It lives
one year only, being the first instance of an _annual vertebrate_. It
spawns in June and July, the eggs are hatched in August, and the fishes
attain their full growth in the months from October to December. In
this stage the sexes are quite alike, both having very small teeth
and feeble jaws. In April the males lose the small teeth, which are
replaced by very long and strong teeth, the jaws themselves becoming
stronger. The teeth of the females remain unchanged. In July and August
all the adults die off, and in September only the fry are to be found.

There are several other genera, closely allied to Gobius, as
_Euctenogobius_, _Lophiogobius_, _Doliichthys_, _Apocryptes_,
_Evorthodus_, _Gobiosoma_ and _Gobiodon_ (with scaleless body)
_Triænophorichthys_.

   SICYDIUM.--Body covered with ctenoid scales of rather small
   size. Cleft of the mouth nearly horizontal, with the upper jaw
   prominent; lips very thick; the lower lip generally with a
   series of minute horny teeth. A series of numerous small teeth
   in upper jaw, implanted in the gum, and generally movable;
   the lower jaw with a series of conical widely-set teeth. Two
   dorsal fins, the anterior with six flexible spines. Ventral fins
   united, and forming a short disk, more or less adherent to the
   abdomen.

Small freshwater fishes inhabiting the rivers and rivulets of the
islands of the tropical Indo-Pacific. About twelve species are known;
one occurs in the West Indies. _Lentipes_ from the Sandwich Islands is
allied to _Sicydium_.

   PERIOPHTHALMUS.--Body covered with ctenoid scales of small or
   moderate size. Cleft of the mouth nearly horizontal, with the
   upper jaw somewhat longer. Eyes very close together, immediately
   below the upper profile, prominent, but retractile, with a
   well-developed outer eyelid. Teeth conical, vertical in both
   jaws. Two dorsal fins, the anterior with flexible spines; caudal
   fin with the lower margin oblique; base of the pectoral fin
   free, with strong muscles. Ventral fins more or less coalesced.
   Gill-openings narrow.

The fishes of this genus, and the closely-allied _Boleophthalmus_,
are exceedingly common on the coasts of the tropical Indo-Pacific,
especially on parts covered with mud or fucus. During ebb they leave
the water and hunt for small crustaceans, and other small animals
disporting themselves on the ground which is left uncovered by the
receding water. With the aid of their strong pectoral and ventral fins
and their tail, they hop freely over the ground, and escape danger
by rapid leaps. The peculiar construction of their eyes, which are
very movable, and can be thrust far out of their sockets, enables
them to see in the air as well as in the water; when the eyes are
retracted they are protected by a membranous eyelid. These fishes
are absent in the eastern parts of the Pacific and on the American
side of the Atlantic; but singularly enough one species reappears
on the West African coast. About seven species are known (including
_Boleophthalmus_), _P. koelreuteri_ being one of the most common fishes
of the Indian Ocean.

  [Illustration: Fig. 221.--Periophthalmus koelreuteri.]

   ELEOTRIS.--Body scaly; eyes of moderate size, lateral, not
   prominent. Teeth small. Two dorsal fins, the anterior generally
   with six spines. Ventrals not united, though close together,
   with one spine and five rays.

About sixty species are known from the tropics, only a few extending
into the temperate zone. As regards form, they repeat almost all the
modifications observed among the Gobies, from which they differ only
in having the ventral fins non-coalescent. On the whole they are
somewhat larger than the Gobies, and rather freshwater than marine
species, some of them being abundant in the rivulets of the islands of
the Indo-Pacific and Atlantic. Others have even penetrated into the
inland-waters of the African continent.

   TRYPAUCHEN.--Body elongate, covered with minute scales;
   head compressed, with a deep cavity on each side, above the
   operculum. Teeth small, in a band. One dorsal, the spinous
   portion composed of six spines; dorsal and anal fins continuous
   with the caudal, ventral fins united.

Small fishes of singular aspect, from the East Indian coasts. Three
species, of which _T. vagina_ is common.

   CALLIONYMUS.--Head and anterior part of the body depressed,
   the rest cylindrical, naked. Snout pointed, with the cleft
   of the mouth narrow, horizontal, and with the upper jaw very
   protractile. Eyes rather large, more or less directed upwards.
   Teeth very small, palate smooth. A strong spine at the angle of
   the præoperculum. Two dorsal fins, the anterior with three or
   four flexible spines; ventrals five-rayed, widely apart from
   each other. Gill-openings very narrow, generally reduced to a
   foramen on the upper side of the operculum.

The “Dragonets” are small, and generally beautifully coloured marine
fishes, inhabitants of the coasts of the temperate zone of the
Old World; the minority of species live in tropical parts of the
Indo-Pacific; and these seem to descend to somewhat greater depths
than the littoral species of the northern hemisphere. Secondary sexual
characters are developed in almost all the species, the mature males
having the fin-rays prolonged into filaments, and the fin-membranes
brightly ornamented. On the British coast one species (_C. draco_) is
very common, and locally called “Skulpin.” About thirty species are
known, many of which have the præopercular spine armed with processes
or barbs. _Vulsus_ is allied to _Callionymus_.

Other genera belonging to this family are--_Benthophilus_ from the
Caspian Sea; _Amblyopus_, _Orthostomus_, _Platyptera_, _Luciogobius_,
_Oxymetopon_, and, perhaps, _Oxuderces_.


            TENTH DIVISION--ACANTHOPTERYGII BLENNIIFORMES.

_Body low, sub-cylindrical or compressed, elongate. Dorsal fin very
long; the spinous portion of the dorsal, if distinct, is very long,
as well developed, as the soft, or much more; sometimes the entire
fin is composed of spines only; anal more or less long; caudal fin
subtruncated or rounded, if present. Ventral fins thoracic or jugular,
if present._


                        FIRST FAMILY--CEPOLIDÆ.

_Body very elongate, compressed, covered with very small cycloid
scales; eyes rather large, lateral. Teeth of moderate size. No bony
stay for the angle of the præoperculum. One very long dorsal fin,
which, like the anal, is composed of soft rays. Ventrals thoracic,
composed of one spine and five rays. Gill-opening wide. Caudal vertebræ
exceedingly numerous._

The “Band-fishes” (_Cepola_) are small marine fishes, belonging
principally to the fauna of the northern temperate zone; in the Indian
Ocean the genus extends southwards to Pinang. The European species (_C.
rubescens_) is found in isolated examples on the British coast, but is
less scarce in some years than in others. These fishes are of a nearly
uniform red colour.


                     SECOND FAMILY--TRICHONOTIDÆ.

_Body elongate, sub-cylindrical, covered with cycloid scales of
moderate size. Eyes directed upwards. Teeth in villiform bands. No
bony stay for the angle of the præoperculum. One long dorsal fin, with
simple articulated rays, and without a spinous portion; anal long.
Ventrals jugular, with one spine and five rays. Gill-opening very wide.
The number of caudal vertebræ much exceeding that of the abdominal._

Small marine fishes, belonging to two genera only, _Tricho__notus_
(_setigerus_) from Indian Seas, with some of the anterior dorsal rays
prolonged into filaments; and _Hemerocoetes_ (_acanthorhynchus_) from
New Zealand, and sometimes found far out at sea on the surface.

                    THIRD FAMILY--HETEROLEPIDOTIDÆ.

_Body oblong, compressed, scaly; eyes lateral; cleft of the mouth
lateral; dentition feeble. The angle of the præoperculum connected by a
bony stay with the infraorbital ring. Dorsal long, with the spinous and
soft portions equally developed; anal elongate. Ventrals thoracic, with
one spine and five rays._

  [Illustration: Fig. 222.--Scale from the lateral line of
  Hemerocœtes acanthorhynchus, with lacerated margin.]

  [Illustration: Fig. 223.--_Chirus hexagrammus_, from Japan.]

Small shore-fishes, characteristic of the fauna of the Northern
Pacific, some of the species occurring on the American as well as
Asiatic side. They have been referred to several genera, as

   CHIRUS, which is distinguished by the presence of several
   lateral lines;

   OPHIODON, with one lateral line only, cycloid scales, and
   slightly armed præoperculum;

   AGRAMMUS, with one lateral line only, ctenoid scales, and
   unarmed præoperculum; and

   ZANIOLEPIS, with one lateral line and minute comb-like scales.


                       FOURTH FAMILY--BLENNIIDÆ.

_Body elongate, low, more or less cylindrical, naked or covered with
scales, which generally are small. One, two, or three dorsal fins
occupying nearly the whole length of the back, the spinous portion,
if distinct, being as much developed as the soft, or more; sometimes
the entire fin is composed of spines; anal fin long. Ventrals jugular,
composed of a few rays, and sometimes rudimentary or entirely absent.
Pseudobranchiæ generally present._

Littoral forms of great generic variety, occurring abundantly in
all temperate and tropical seas. Some of the species have become
acclimatised in fresh water, and many inhabit brackish water. With
very few exceptions they are very small, some of the smallest
fishes belonging to the family of “Blennies.” One of the principal
characteristics of the Blennies is the ventral fin, which is formed by
less than five rays, and has a jugular position. The Blennies have this
in common with many Gadoids, and it is sometimes difficult to decide to
which of these two families a fish should be referred. In such doubtful
cases the presence of the pseudobranchiæ (which are absent in Gadoids)
may be of assistance.

In many Blennies the ventral fins have ceased to have any function, and
become rudimentary, or are even entirely absent. In others the ventral
fins, although reduced to cylindrical stylets, possess a distinct
function, and are used as organs of locomotion, by the aid of which the
fish moves rapidly over the bottom.

The fossil forms are scarcely known; _Pterygocephalus_ from Monte Bolca
appears to have been a Blennioid.

   ANARRHICHAS.--Body elongate, with rudimentary scales; snout
   rather short; cleft of the mouth wide; strong conical teeth in
   the jaws, those on the sides with several pointed tubercles; a
   biserial band of large molar teeth on the palate. Dorsal fin
   long, with flexible spines; caudal separate. Ventrals none.
   Gill-openings wide.

The “Sea-wolf,” or “Sea-cat” (_A. lupus_), is a gigantic Blenny,
attaining to a length of more than six feet. With its enormously strong
tubercular teeth it is able to crush the hardest shells of Crustaceans
or Mollusks, on which it feeds voraciously. It is an inhabitant of the
northern seas, like two other allied species, all of which are esteemed
as food by the inhabitants of Iceland and Greenland. Two other species
of Sea-wolves occur in the corresponding latitudes of the North Pacific.

  [Illustration: Fig. 224.--Teeth of the Wolf-fish, _Anarrhichas
  lupus_.]

   BLENNIUS.--Body moderately elongate, naked; snout short. A
   single dorsal, without detached portion; ventrals jugular,
   formed by a spine and two rays. Cleft of the mouth narrow; a
   single series of immovable teeth in the jaws; generally a curved
   tooth behind this series in both jaws, or in the lower only. A
   more or less developed tentacle above the orbit. Gill-opening
   wide.

About forty species of Blennius (in the restricted generic sense)
are known from the northern temperate zone, the tropical Atlantic,
Tasmania, and the Red Sea. But in the tropical Indian Ocean they are
almost entirely absent, and replaced by other allied genera. Three
species, found near the Sandwich Islands, are immigrants into the
Pacific from the American Continent. They generally live on the coast,
or attach themselves to floating objects, some species leading a
pelagic life, hiding themselves in floating seaweed, in which they
even propagate their species. All species readily accustom themselves
to fresh water, and some (_B. vulgaris_) have become entirely
acclimatised in inland lakes. British species are _B. gattorugine_
(growing to a length of twelve inches), _B. ocellaris_, _B. galerita_,
and _B. pholis_, the common “Shanny.”

_Chasmodes_ is a genus allied to _Blennius_, from the Atlantic coasts
of temperate North America.

  [Illustration: Fig. 225.--Petroscirtes bankieri, from Hong-Kong.]

   PETROSCIRTES.--Body moderately elongate, naked. Snout generally
   short. A single dorsal fin; ventrals composed of two or three
   rays. Cleft of the mouth narrow; a single series of immovable
   teeth in the jaws; a strong curved canine tooth behind this
   series, that of the lower jaw much stronger than that of the
   upper. Head sometimes with tentacles. Gill-opening reduced to a
   small fissure above the root of the pectoral.

Thirty species, from the tropical Indo-Pacific, of small size.

  [Illustration: Fig. 226.--Dentition of the same, enlarged.]

   SALARIAS.--Body moderately elongate, naked; snout short, with
   transverse cleft of the mouth; a series of numerous small
   teeth in the jaws, implanted in the gum and movable; generally
   a curved canine tooth on each side of the lower jaw, behind
   the series of small teeth. Dorsal fin continuous, sometimes
   divided into two portions by a more or less deep notch without a
   detached anterior part. Ventral fins with two or three rays. A
   tentacle above the orbit. Gill-openings wide.

Sixty species are known from the tropical zone, extending northwards to
Madeira, southwards to Chile and Tasmania. In certain individuals of
some of the species a longitudinal cutaneous crest is developed; all
young individuals lack it, and in some other species it is invariably
absent. Singularly enough this crest is not always a sexual character,
as one might have supposed from analogy, but in some species at least
it is developed in both sexes. Mature males, however, have generally
higher dorsal fins and a more intense and variegated coloration than
females and immature males, as is also the case in _Blennius_.

   CLINUS.--Body moderately elongate, covered with small scales;
   snout rather short; a narrow band or series of small teeth in
   the jaws and on the palate. Dorsal fin formed by numerous spines
   and a few soft rays, without a detached anterior portion; anal
   spines two. Ventrals with two or three rays. A tentacle above
   the orbit. Gill-opening wide.

Thirty species, from the coasts of tropical America and the southern
temperate zone. Three other genera are closely allied to Clinus, viz.
_Cristiceps_ and _Cremnobates_, in which the three anterior dorsal
spines are detached from the rest of the fin; and _Tripterygium_, with
three distinct dorsal fins, of which the two anterior are spinous. The
species of these genera are as numerous as those of _Clinus_, occurring
in many parts of tropical seas, in the Mediterranean, and being
especially well represented in South Australia and New Zealand.

   STICHÆUS.--Body elongate, covered with very small scales;
   lateral line more or less distinct, sometimes several lateral
   lines. Snout short; very small teeth in the jaws, and generally
   on the palate. Dorsal fin long, formed by spines only. Ventrals
   with two or three rays. Caudal fin distinct. Gill-openings
   rather wide.

Small fishes, peculiar to the coasts near the arctic circle, ranging
southwards to the coasts of Japan and Scandinavia. Ten species.

   BLENNIOPS.--Body moderately elongate, covered with very small
   scales; lateral line none. Snout short; small teeth in the
   jaws, none on the palate. Dorsal fin long, formed by spines
   only. Ventrals with one spine and three rays. Caudal distinct.
   Gill-openings of moderate width, the gill-membranes coalescent
   across the isthmus.

A fine but not common kind of Blenny (_B. ascanii_), from the British
and Scandinavian coasts.

   CENTRONOTUS.--Body elongate, covered with very small scales;
   lateral line none. Snout short; very small teeth in the jaws.
   Dorsal fin long, formed by spines only. Ventrals none or
   rudimentary; caudal separate. Gill-openings of moderate width,
   gill-membranes coalescent.

Ten species are known from the northern coasts; southwards the genus
extends to the coasts of France, New York, California, and Japan. _C.
gunellus_, or the “Gunnel-fish” or “Butter-fish,” is common on the
British coasts. _Apodichthys_ is allied to _Centronotus_, but the
vertical fins are confluent; and a very large, excavated, pen-like
spine lies hidden in a pouch in front of the anal fin. This spine is
evidently connected in some way with the generative organs, as a furrow
leads from the orifice of the oviduct to the groove of the spine. One
species from the Pacific coast of North America. _Xiphidion_ is another
closely allied genus from the same locality.

   CRYPTACANTHODES.--Body very elongate, naked, with a single
   lateral line. Head with the muciferous system well developed.
   Eye rather small. Conical teeth in the jaws, on the vomer
   and palatine bones. One dorsal formed by spines only; caudal
   connected with dorsal and anal. Ventrals none. Gill-opening of
   moderate width, with the gill-membranes joined to the isthmus.

One species (_C. maculatus_) from the Atlantic coasts of North America.

   PATÆCUS.--Body oblong, elevated anteriorly; snout short, with
   subvertical anterior profile; minute teeth in the jaws and on
   the vomer. Dorsal fin with the anterior spines strong and long,
   continuous with the caudal; ventrals none. Gill-openings wide.

  [Illustration: Fig. 227.--Patæcus fronto.]

Three species of this singular form are known from South and West
Australia.

   ZOARCES.--Body elongate, with the scales rudimentary; conical
   teeth in the jaws. Dorsal fin long, with a depression on the
   tail, which is formed by a series of spines much shorter than
   the rays. No other fin-spines. No separate caudal fin. Ventrals
   short, formed by three or four rays. Gill-openings wide.

Two species are known, one from the European, and the other from the
North American side of the Atlantic. The former, _Z. viviparus_, is
well known by the name of “Viviparous Blenny;” as is signified by this
name it produces its young alive. These are so matured at the time of
their birth that on their first exclusion they swim about with the
utmost agility. No fewer than from two to three hundred young are
sometimes produced by one female, and the abdomen of the mother is so
distended before parturition that it is impossible to touch it without
causing them to be extruded. Full grown individuals are about twelve
inches long, but the American species (_Z. anguillaris_) attains to a
length of two or three feet.

Other genera of the family of Blennoids are:--_Blennophis_,
_Nemophis_, _Plagiotremus_, _Neoclinus_, _Cebidichthys_, _Myxodes_,
_Heterostichus_, _Dictyosoma_, _Lepidoblennius_, _Dactyloscopus_,
_Gunellichthys_, _Urocentrus_, _Stichæopsis_, _Sticharium_,
_Notograptus_, _Pholidichthys_, and _Pseudoblennius_.


                     FIFTH FAMILY--ACANTHOCLINIDÆ.

_Body elongate, low, compressed, covered with small scales. One
dorsal fin, occupying nearly the whole of the back, and chiefly
composed of spines. Anal fin long, with numerous spines. Ventrals
jugular, composed of a few rays only._

Of this family one fish only is known (_Acanthoclinus littoreus_),
a small Blenny abundant on the coast of New Zealand.


                     SIXTH FAMILY--MASTACEMBELIDÆ.

_Body elongate, eel-like, covered with very small scales. Mandible
long, but little moveable. Dorsal fin very long, the anterior portion
composed of numerous short isolated spines; anal fin with spines
anteriorly. Ventrals none. The humeral arch is not suspended from the
skull. Gill-openings reduced to a slit at the lower part of the side of
the head._

Freshwater-fishes characteristic of and almost confined to the Indian
region. The structure of the mouth and of the branchial apparatus, the
separation of the humeral arch from the skull, the absence of ventral
fins, the anatomy of the abdominal organs, affords ample proof that
these fishes are Acanthopterygian eels. Their upper jaw terminates
in a pointed moveable appendage, which is concave and transversely
striated inferiorly in _Rhynchobdella_, and without transverse striæ in
_Mastacembelus_: the only two genera of this family. Thirteen species
are known, of which _Rh. aculeata_, _M. pancalus_ and _M. armatus_
are extremely common, the latter attaining to a length of two feet.
Outlying species are _M. aleppensis_ from Mesopotamia and Syria, and
_M. cryptacanthus_, _M. marchei_, and _M. niger_, from West Africa.

  [Illustration: Fig. 228.--Mastacembelus argus, from Siam.]


           ELEVENTH DIVISION--ACANTHOPTERYGII MUGILIFORMES.

_Two dorsal fins more or less remote from each other; the anterior
either short, like the posterior, or composed of feeble spines. Ventral
fins with one spine and five rays, abdominal._


                       FIRST FAMILY--SPHYRÆNIDÆ.

_Body elongate, sub-cylindrical, covered with small cycloid scales;
lateral line continuous. Cleft of the mouth wide, armed with strong
teeth. Eye lateral, of moderate size. Vertebræ twenty-four._

This family consists of one genus only, _Sphyræna_, generally called
“Barracudas,” large voracious fishes from the tropical and sub-tropical
seas, which prefer the vicinity of the coast to the open sea. They
attain to a length of eight feet, and a weight of forty pounds;
individuals of this large size are dangerous to bathers. They are
generally used as food, but sometimes (especially in the West Indies)
their flesh assumes poisonous qualities, from having fed on smaller
poisonous fishes. Seventeen species.

The Barracudas existed in the tertiary epoch, their remains being
frequently found at Monte Bolca. Some other fossil genera have been
associated with them, but as they are known from jaws and teeth
or vertebræ only, their position in the system cannot be exactly
determined; thus _Sphyrænodus_ and _Hypsodon_ from the chalk of Lewes,
and the London clay of Sheppey. The American _Portheus_ is allied to
_Hypsodon_. Another remarkable genus from the chalk, _Saurocephalus_,
has been also referred to this family.[44]


                      SECOND FAMILY--ATHERINIDÆ.

_Body more or less elongate, sub-cylindrical, covered with scales of
moderate size; lateral line indistinct. Cleft of the mouth of moderate
width, with the dentition feeble. Eye lateral, large or of moderate
size. Gill-openings wide. Vertebræ very numerous._

Small carnivorous fishes inhabiting the seas of the temperate and
tropical zones; many enter fresh water, and some have been entirely
acclimatised in it. This family seems to have been represented in the
Monte Bolca formation by _Mesogaster_.

   ATHERINA.--Teeth very small; scales cycloid. The first dorsal is
   short and entirely separated from the second. Snout obtuse, with
   the cleft of the mouth straight, oblique, extending to or beyond
   the anterior margin of the eye.

The Atherines are littoral fishes, living in large shoals, which habit
has been retained by the species acclimatised in fresh water. They
rarely exceed a length of six inches, but are nevertheless esteemed
as food. From their general resemblance to the real Smelt they are
often thus misnamed, but may always be readily recognised by their
small first spinous dorsal fin. The young, for some time after they
are hatched, cling together in dense masses, and in numbers almost
incredible. The inhabitants of the Mediterranean coast of France call
these newly hatched Atherines “Nonnat” (unborn). Some thirty species
are known, of which _A. presbyter_ and _A. boyeri_ occur on the British
coast.

   ATHERINICHTHYS, distinguished from _Atherina_ in having the
   snout more or less produced; and the cleft of the mouth
   generally does not extend to the orbit.

These Atherines are especially abundant on the coasts and in the fresh
waters of Australia and South America. Of the twenty species known,
several attain a length of eighteen inches and a weight of more than a
pound. All are highly esteemed as food; but the most celebrated is the
“Pesce Rey” of Chile (_A. laticlavia_).

   TETRAGONURUS.--Body rather elongate, covered with strongly
   keeled and striated scales. The first dorsal fin is composed
   of numerous feeble spines, and continued on to the second.
   Lower jaw elevated, with convex dental margin, and armed with
   compressed, triangular, rather small teeth, in a single series.

This very remarkable fish is more frequently met with in the
Mediterranean than in the Atlantic, but generally scarce. Nothing is
known of its habits; when young it is one of the fishes which accompany
Medusæ, and, therefore, it must be regarded as a pelagic form.
Probably, at a later period of its life, it descends to greater depths,
coming to the surface at night only. It grows to a length of eighteen
inches.


                        THIRD FAMILY--MUGILIDÆ.

_Body more or less oblong and compressed, covered with cycloid scales
of moderate size; lateral line none. Cleft of the mouth narrow or of
moderate width, without or with feeble teeth. Eye lateral, of moderate
size. Gill-opening wide. The anterior dorsal fin composed of four stiff
spines. Vertebræ twenty-four._

The “Grey Mullets” inhabit in numerous species and in great numbers the
coasts of the temperate and tropical zones. They frequent brackish
waters, in which they find an abundance of food which consists chiefly
of the organic substances mixed with mud or sand; in order to prevent
larger bodies from passing into the stomach, or substances from passing
through the gill-openings, these fishes have the organs of the pharynx
modified into a filtering apparatus. They take in a quantity of sand or
mud, and, after having worked it for some time between the pharyngeal
bones, they eject the roughest and indigestible portion of it. The
upper pharyngeals have a rather irregular form; they are slightly
arched, the convexity being directed towards the pharyngeal cavity,
tapering anteriorly and broad posteriorly. They are coated with a thick
soft membrane, which reaches far beyond the margin of the bone, at
least on its interior posterior portion; this membrane is studded all
over with minute horny cilia. The pharyngeal bone rests upon a large
fatty mass, giving it a considerable degree of elasticity. There is a
very large venous sinus between the anterior portion of the pharyngeal
and the basal portion of the branchial arches. Another mass of fat,
of elliptical form, occupies the middle of the roof of the pharynx,
between the two pharyngeal bones. Each branchial arch is provided
on each side, in its whole length, with a series of closely-set
gill-rakers, which are laterally bent downwards, each series closely
fitting into the series of the adjoining arch; they constitute together
a sieve, admirably adapted to permit a transit for the water, retaining
at the same time every other substance in the cavity of the pharynx.

The lower pharyngeal bones are elongate, crescent-shaped, and
broader posteriorly than anteriorly. Their inner surface is concave,
corresponding to the convexity of the upper pharyngeals, and provided
with a single series of lamellæ, similar to those of the branchial
arches, but reaching across the bone from one margin to the other.

The intestinal tract shows no less peculiarities. The lower portion
of the œsophagus is provided with numerous long thread-like papillæ,
and continued into the oblong-ovoid membranaceous cœcal portion of the
stomach, the mucosa of which forms several longitudinal folds. The
second portion of the stomach reminds one of the stomach of birds;
it communicates laterally with the other portion, is globular, and
surrounded by an exceedingly strong muscle. This muscle is not divided
into two as in birds, but of great thickness in the whole circumference
of the stomach, all the muscular fasciculi being circularly arranged.
The internal cavity of this stomach is rather small, and coated with a
tough epithelium, longitudinal folds running from the entrance opening
to the pyloric, which is situated opposite to the other. A low circular
valve forms a pylorus. There are five rather short pyloric appendages.
The intestines make a great number of circumvolutions, and are seven
feet long in a specimen thirteen inches in length.

  [Illustration: Fig. 229.--Mugil proboscideus.]

Some seventy species of Grey Mullets are known, the majority of
which attain to a weight of about four pounds, but there are many
which grow to ten and twelve pounds. All are eaten, and some even
esteemed, especially when taken out of fresh water. If attention
were paid to their cultivation, great profits could be made by fry
being transferred into suitable backwaters on the shore, in which
they rapidly grow to a marketable size. Several species are more or
less abundant on the British coasts, as _Mugil octo-radiatus_ (Fig.
105, p. 254), _M. capito_, _M. auratus_ (Fig. 106, p. 254), and _M.
septentrionalis_ (Fig. 107, p. 254), which, with the aid of the
accompanying figures, and by counting the rays of the anal fin, may be
readily distinguished--_M. octo-radiatus_ having eight, and _M. capito_
and _M. auratus_ nine soft rays. A species inhabiting fresh waters of
Central America (_M. proboscideus_) has the snout pointed and fleshy,
thus approaching certain other freshwater and littoral Mullets, which,
on account of a modification of the structure of the mouth, have been
formed into a distinct genus, _Agonostoma_. _Myxus_ comprises Mullets
with teeth more distinct than in the typical species.

This genus existed in the tertiary epoch, remains of a species having
been found in the gypsum of Aix, in Provence.


          TWELFTH DIVISION--ACANTHOPTERYGII GASTROSTEIFORMES.

_The spinous dorsal is composed of isolated spines if present;
the ventrals are either thoracic or have an abdominal position in
consequence of the prolongation of the pubic bones which are attached
to the humeral arch. Mouth small, at the end of the snout which is
generally more or less produced._


                      FIRST FAMILY--GASTROSTEIDÆ.

_Body elongate, compressed. Cleft of the mouth oblique; villiform
teeth in the jaws. Opercular bones not armed; infraorbitals covering
the cheek; parts of the skeleton forming incomplete external mails.
Scales none, but generally large scutes along the side. Isolated spines
in front of the soft dorsal fin. Ventral fins abdominal, joined to
the pubic bone, composed of a spine and a small ray. Branchiostegals
three._

  [Illustration: Fig. 230.--Gastrosteus noveboracensis.]

Of “Sticklebacks” (_Gastrosteus_) about ten species are satisfactorily
known, one of which (_G. spinachia_) lives in salt and brackish water,
whilst the others inhabit principally fresh waters, although they all
are able to exist in the sea. They are confined to the Temperate and
Arctic zones of the northern hemisphere. The British freshwater species
are the Three-spined Stickleback (_G. aculeatus_), which sometimes,
especially in Central Europe, lacks scutes, sometimes has a series of
scutes along the side of the body; the Four-spined Stickleback (_G.
spinulosus_) and the Nine-spined Stickleback (_G. pungitius_). The
commonest North American species is _G. noveboracensis_. The habits
of all the freshwater species are very similar. The common European
species (_G. aculeatus_) is an active and greedy little fish, extremely
destructive to the fry of other species, and consequently injurious
in ponds where these are sought to be preserved. It is scarcely to
be conceived what damage these little fishes do, and how greatly
detrimental they are to the increase of all the fishes in general among
which they live; for it is with the utmost industry, sagacity, and
greediness that they seek out and destroy all the young fry that come
their way. A small Stickleback, kept in an aquarium, devoured, in five
hours’ time, seventy-four young dace, which were about a quarter of
an inch long, and of the thickness of a horse hair. Two days after it
swallowed sixty-two; and would, probably, have eaten as many every day
could they have been procured. The Stickleback sometimes swarms in
prodigious numbers. Pennant states that at Spalding, in Lincolnshire,
there was once in seven years amazing shoals, which appear in the
Welland, coming up the river in the form of a vast column. The quantity
may, perhaps, be conceived from the fact that a man employed in
collecting them, gained, for a considerable time, four shillings a-day
by selling them at the rate of a halfpenny a bushel. Costa, who studied
the manners of these small fishes, relates that, on the approach of
spawning time, the male builds a nest of stalks of grass and other
matters in a hollow of the bottom, a little above three inches wide and
about six inches and a half deep, creeping over the materials on his
belly, and cementing them with the mucus that exudes from his skin.
The bottom of the nest is first laid, then the sides are raised, and
lastly the top is covered over. A small hole is left on one side for
an entrance. When the erection is complete, he seeks out a female, and
conducting her, Costa says, with many caresses, to the nest, introduces
her by the door into the chamber. In a few minutes she has laid two or
three eggs, after which she bores a hole on the opposite side of the
nest to that by which she entered, and makes her escape. The nest has
now two doors, and the eggs are exposed to the cool stream of water,
which, entering by one door flows out at the other. Next day the male
goes again in quest of a female, and sometimes brings back the same,
sometimes finds a new mate. This is repeated until the nest contains
a considerable number of eggs, and each time the male rubs his side
against the female and passes over the eggs. Next the male watches
a whole month over his treasure, defending it stoutly against all
invaders, and especially against his wives, who have a great desire
to get at the eggs. When the young are hatched and able to do for
themselves his cares cease.

The Sea-Stickleback (_G. spinachia_) is likewise a nest builder,
choosing for its operations especially the shallows of brackish water,
which are covered with _Zostera_.


                     SECOND FAMILY--FISTULARIIDÆ.

_Fishes of greatly elongated form; the anterior bones of the skull
are much produced, and form a long tube, terminating in a narrow mouth.
Teeth small; scales none, or small. The spinous dorsal fin is either
formed by feeble isolated spines or entirely absent; the soft dorsal
and anal of moderate length, ventral fins thoracic or abdominal,
composed of five or six rays, without spine; if abdominal, they are
separate from the pubic bones, which remain attached to the humeral
arch. Branchiostegals five._

The “Flute-mouths” are also frequently called “Pipe-fishes,” a name
which they have in common with the Syngnathidæ. They are gigantic
marine Sticklebacks, living near the shore, from which they are
frequently driven into the open sea; some of the species, therefore,
have a wide geographical range. Probably all enter brackish water. They
are distributed over the whole of the tropical and sub-tropical parts
of the Atlantic and Indo-Pacific. The species are few in number, but
some of them are very common.

This family is well represented in Eocene formations; some of the
remains belonging to the existing genera, _Fistularia_, _Aulostoma_,
and _Auliscops_, the two former of which occur not rarely at Monte
Bolca and in the schists of Glaris. Well-preserved remains of
_Auliscops_ have been found in the Marl-slates of the highlands of
Padang in Sumatra. Extinct genera from Monte Bolca are _Urosphen_, the
cylindrical body of which is terminated by a large cuneiform fin; and
_Rhamphosus_, which has an immense spinous ray, denticulated behind,
inserted on the nape.

   FISTULARIA.--Body scaleless; caudal fin forked, with the two
   middle rays produced into a filament; no free dorsal spines.

Three species are known, common on the shores of the Tropical Atlantic
(_F. tabaccaria_) and Indian Oceans (_F. serrata_ and _F. depressa_);
they attain to a length of from four to six feet.

The anterior portion of the vertebral column shows the same peculiarity
as in _Dactylopterus_; it is a long compressed tube, composed of four
elongate vertebræ, which are perfectly anchylosed; each of them has
a pair of small foramina for blood-vessels. The neural spines and
parapophyses of this tubiform portion are confluent into thin laminæ,
the lateral of which are wing-like, and expanded in their anterior half.

   AULOSTOMA.--Body covered with small scales. Caudal fin rhombic,
   without prolonged rays; a series of isolated feeble dorsal
   spines. Teeth rudimentary.

Two species from the Tropical Atlantic and Indian Oceans.

   AULISCOPS.--Body naked. Ventrals thoracic. Numerous spines in
   front of the dorsal fin.

One species (_A. spinescens_) from the Pacific coast of North America.
_Aulorhynchus_ from the same sea, and _Aulichthys_ from Japan, are
allied genera.


         THIRTEENTH DIVISION--ACANTHOPTERYGII CENTRISCIFORMES.

_Two dorsal fins; the spinous short, the soft and the anal of moderate
extent. Ventral fins truly abdominal, imperfectly developed._

This division consists of one family, _Centriscidæ_, with two genera.
The fishes belonging to it are very small, marine, and, in consequence
of their limited power of swimming, often driven out into the open
sea. They have the same structure of the mouth and snout as the
Fistulariidæ, but combine with it peculiarities of the shape of body,
of the structure of the vertical fins, and of the relations between
endo- and exo-skeleton, which render them altogether a singular and
interesting type. _Amphisile_ has been found in a fossil state at Monte
Bolca.

   CENTRISCUS.--Body oblong or elevated, compressed, covered with
   small rough scales; lateral line none; some bony strips on the
   side of the back, and on the margin of the thorax and abdomen;
   the former, in one species, are confluent and form a shield.
   Teeth none. Two dorsal fins, the first with one of the spines
   very strong. Ventral fins small, abdominal, composed of five
   soft rays. Four branchiostegals.

  [Illustration: Fig. 231.--Centriscus humerosus.]

Of the four species the most generally known is _C. scolopax_, the
“Trumpet-fish” or “Bellows-fish,” which rarely occurs on the south
coast of England, is more common farther south, and reappears in
Tasmania. The allied _C. gracilis_ is one of the fishes common to the
Mediterranean and Japanese Seas. The species figured, _C. humerosus_,
occurs on the coast of South Australia, and is very scarce.

   AMPHISILE.--Body elongate, strongly compressed, provided with a
   dorsal cuirass, which is formed by portions of the skeleton; the
   longitudinal axis of the tail is not in the same line with that
   of the trunk. Scales none. Teeth none. Two dorsal fins situated
   on the hindmost part of the back; ventral fins rudimentary,
   abdominal. Three or four branchiostegals.

The three species known of this genus are found in the tropical
Indo-Pacific. Their body is so thin that it has the appearance of
being artificially compressed between two sheets of paper; it is
semi-transparent, especially in the region of the air-bladder. The
structure of the vertebral column is extremely singular and unique
among Acanthopterygians. The abdominal portion is more than four
times as long as the caudal; nevertheless it is composed of only
six vertebræ, whilst the latter consists of fourteen. The abdominal
vertebræ are extremely slender, the third alone being nearly as long
as the whole caudal portion; they have a slight ridge superiorly
and inferiorly, and on each side; the whole portion lying in the
uppermost concavity of the dorsal cuirass. The caudal vertebræ are
extremely short, and the strength of their neural and hæmal spines
is in proportion to their size. The dorsal cuirass is not a dermal
production, but formed by modified parts of the endoskeleton; its
composition, the number and condition of its single parts, and,
finally, the first dorsal spine, which in _A. punctulata_ is so
singularly attached to it, favour this opinion. The plates, which
occupy the vertebral line, would correspond to the neural spines, and
the lateral plates on which the ribs are suspended to the parapophyses.
_Amphisile_ may be considered as a Chelonian form among fishes.


         FOURTEENTH DIVISION--ACANTHOPTERYGII GOBIESOCIFORMES.

_No spinous dorsal; the soft and the anal short or of moderate length,
situated on the tail; ventral fins subjugular, with an adhesive
apparatus between them. Body naked._

These fishes are well characterised by their single dorsal fin, and
by their adhesive ventral apparatus, which has only an external
similarity to the organ observed in _Cyclopterus_ and _Liparis_; its
structure is typically different from it. Whilst in those genera the
ventral fins occupy the centre of the disk forming its base, these
fins are here widely apart from each other, as in _Callionymus_,
forming only a portion of the periphery of the disk, which is completed
by a cartilaginous expansion of the coracoid bones. The following
description of its structure is taken from _Sicyases sanguineus_, but
it is essentially the same in all the genera.

The whole disk is exceedingly large, subcircular, longer than broad,
its length being one-third of the whole length of the fish. The central
portion is formed merely by skin, which is separated from the pelvic
or pubic bones by several layers of muscles. The peripheric portion is
divided into an anterior and posterior part by a deep notch behind the
ventrals. The anterior peripheric portion is formed by the four ventral
rays, the membrane between them, and a broad fringe which extends
anteriorly from one ventral to the other; this fringe is a fold of
the skin, containing on each side the rudimentary ventral spine, but
no cartilage. The posterior peripheric portion is suspended on each
side from the coracoid, the upper bone of which is exceedingly broad,
becoming a free movable plate behind the pectoral. A broad cartilage
is firmly attached to it. The lower bone of the coracoid is of a
triangular form, and supports a very broad fold of the skin, extending
from one side to the other, and containing a cartilage which runs
through the whole of that fold. Five processes of the cartilage are
continued into the soft striated margin in which the disk terminates
posteriorly. The surface of the disk is coated with thick epidermis,
like the sole of the foot of higher animals. The epidermis is divided
into many polygonal plates; there are no such plates between the roots
of the ventral fins.

Not less unique is the structure of the bones which have some
relation to this external adhesive apparatus. As exemplified by
_Chorismochismus dentex_ the coracoid is well developed, and, as
usual, composed of two pieces, the upper of which is not suspended from
the humerus, but fixed by a ligament to the hinder margin of the carpal
bones. It is a broad lamella, dilated posteriorly into the cartilage,
which is externally visible; the lower piece is narrower, and fixed to
the extremity of the pubic bone of its side. The pubic bones are united
by suture, and form together a heart-shaped disk, the point of which
is produced backwards. The anterior portion of the disk is concave,
with a bony longitudinal bridge and a feeble transverse ridge. The disk
is fixed to the humeral bones by the convex portions of its anterior
margin, whilst the convex portions of the lateral margins serve as
base for the ventral fins. The latter are composed of one spine, which
is transformed into a broad, thin, and curved plate, hidden below the
skin, and apparently of four rays; but on closer examination we find
that the hidden ray has a longitudinal groove anteriorly, in which
another thinner ray lies concealed. This ray is quite free, and not
joined to the pubic bone.

The fishes belonging to the single family of this division,
_Gobiesocidæ_, are strictly marine but littoral fishes. They are
scattered over the temperate zones of both hemispheres, and more
numerous than between the Tropics. All are of small or very small size.

  [Illustration: Fig. 232.--Gobiesox cephalus.]

The adhesive disk consists of an anterior and posterior division. In
some of the genera the posterior division has no free anterior margin,
the teeth being either all conical, as in _Chorisochismus_ (Cape of
Good Hope) and _Cotylis_ (Red Sea and Indian Ocean); or incisor-like
in both jaws, as in _Sicyases_ (coast of Chili and West Indies); or
incisor-like at least in the lower jaw, as in _Gobiesox_ (West Indies
and Pacific coasts of South America). In other genera the posterior
portion of the adhesive disk has a free anterior margin. Only one
of these genera has incisor-like teeth, viz. _Diplocrepis_ from New
Zealand. In the remaining genera, _Crepidogaster_ (from Tasmania and
South Australia), _Trachelochismus_ (from New Zealand and the Fiji
Islands), _Lepadogaster_, and _Leptopterygius_, the teeth are very
small and fine. The two last genera are European, and _Lepadogaster_ at
least is common on the Southern British coasts. The three species known
as British--_L. gouanii_, _L. candollii_, and _L. bimaculatus_--are
prettily coloured, but subject to great variation.

  [Illustration: Fig. 233.--Diplocrepis puniceus.]


           FIFTEENTH DIVISION--ACANTHOPTERYGII CHANNIFORMES.

_Body elongate, covered with scales of moderate size; no spine in any
of the fins; dorsal and anal long. No superbranchial organ, only a bony
prominence on the anterior surface of the hyomandibular._

These fishes belong to the single family _Ophiocephalidæ_,
Freshwater-fishes characteristic of the Indian region, which, however,
have found their way into Africa, where they are represented by one or
two species. Thirty-one species are known altogether, most of which
are extremely abundant; some attain to a length of more than two feet.
Like other tropical freshwater fishes, they are able to survive
droughts, living in semi-fluid mud, or lying in a torpid state below
the hard-baked crusts of the bottom of a tank from which every drop
of water has disappeared. Respiration is probably entirely suspended
during the state of torpidity, but whilst the mud is still soft enough
to allow them to come to the surface, they rise at intervals to take in
a quantity of air, by means of which their blood is oxygenised. This
habit has been observed in some species to continue also to the period
of the year in which the fish lives in normal water, and individuals
which are kept in a basin and prevented from coming to the surface
and renewing the air for respiratory purposes, are suffocated. The
particular manner in which the accessory branchial cavity participates
in respiratory functions is not known. It is a simple cavity, without
an accessory branchial organ, the opening of which is partly closed by
a fold of the mucous membrane.

  [Illustration: Fig. 234.--Ophiocephalus striatus, India.]


        SIXTEENTH DIVISION--ACANTHOPTERYGII LABYRINTHIBRANCHII.

_Body compressed, oblong or elevated, with scales of moderate size. A
superbranchial organ in a cavity accessory to that of the gills._


                      FIRST FAMILY--LABYRINTHICI.

_Dorsal and anal spines present, but in variable numbers; ventrals
thoracic. Lateral line absent, or more or less distinctly interrupted.
Gill-opening rather narrow, the gill-membranes of both sides
coalescent below the isthmus, and scaly; gills four; pseudobranchiæ
rudimentary or absent._

  [Illustration: Fig. 235.--Superbranchial organ of Anabas.]

Freshwater-fishes of the Cyprinoid division of the Equatorial zone.
They possess the faculty of being able to live for some time out of
the water, or in thick or hardened mud, in a still greater degree than
the fishes of the preceding family. In the accessory branchial cavity
there is lodged a laminated organ which evidently has the function
of assisting in the oxygenisation of the blood. In _Anabas_ it is
formed by several exceedingly thin bony laminæ, similar in form to the
auricle, and concentrically situated one above the other, the innermost
being the largest. The degree in which these laminæ are developed
is dependent on age. In specimens from one inch and a half to two
inches and a half long there are only two such laminæ, a third being
indicated by a small protuberance at the central base of the second
or outer laminæ. In specimens of from three to four inches in length
the third lamina is developed, covering one-half of the second. The
edges of all the laminæ are straight, not valanced. In specimens of
from four to five inches a fourth lamina makes its appearance in the
basal centre of the third lamina. The other laminæ continue to grow in
their circumference, and their edges now become undulated and slightly
frilled. Cuvier and Valenciennes have examined still larger specimens.
The figure given by them and reproduced here was taken from a specimen
six or seven inches long, and shows the superbranchial organ composed
of six laminæ.

The air-bladder of the majority of these fishes is very large,
extending far into the tail, and, therefore, divided behind by the
hæmal spines into two lateral portions.

The Labyrinthici are generally of small size; they are capable of being
domesticated, and some of them deserve particular attention on account
of the dazzling beauty of their colours or the flavour of their flesh.

   ANABAS.--Body compressed, oblong; præorbital and orbitals
   serrated. Small teeth in the jaws and on the vomer; none on
   the palatines. Dorsal and anal spines numerous. Lateral line
   interrupted.

The “Climbing Perch” (_A. scandens_) is generally distributed over
the Indian Region, and well known from its faculty of moving for some
distance over land, and even up inclined surfaces. In 1797 Daldorf, in
a memoir communicated to the Linnean Society of London, mentions that
in 1791 he had himself taken an Anabas in the act of ascending a palm
tree which grew near a pond. The fish had reached the height of five
feet above the water, and was going still higher. In the effort to do
this it held on to the bark of the tree by the preopercular spines,
bent its tail, and stuck in the spines of the anal; then released its
head, and, raising it, took a new hold with the preoperculum higher up.
The fish is named in the Malayan language the “Tree Climber.” It rarely
attains a length of seven inches.

_Spirobranchus_ from the Cape, and _Ctenopoma_ from Tropical Africa,
represent _Anabas_ in that continent.

   POLYACANTHUS.--Body compressed, oblong; operculum without spines
   or serrature; cleft of the mouth small, more or less oblique,
   not extending beyond the vertical from the orbit, and little
   protractile. Small fixed teeth in the jaws, none on the palate.
   Dorsal and anal spines numerous; the soft dorsal and anal,
   the caudal, and the ventral, more or less elongate in mature
   specimens. Caudal rounded. Lateral line interrupted or absent.

This genus is represented chiefly in the East Indian Archipelago; seven
species are known; some of them have been domesticated on account of
the beauty of their colours, and several varieties have been produced.
One of them is to be mentioned, as, under the name of “Paradise-fish,”
it has been introduced into the aquaria of Europe, where it readily
breeds. It was known already to Lacépède, and has been mentioned since
his time in all ichthyological works as _Macropus viridi-auratus_.
In adult males some of the rays, and especially the caudal lobes, are
much prolonged.

   OSPHROMENUS.--Body compressed, more or less elevated; operculum
   without spine or serrature. Small fixed teeth in the jaws, none
   on the palate. Dorsal spines in small or moderate number; anal
   spines in moderate or great number; ventral fins with the outer
   ray very long, filiform. Lateral line not interrupted or absent.

  [Illustration: Fig. 236.--Osphromenus olfax.]

To this genus belongs the celebrated “Gourami” (_Osphromenus olfax_),
reputed to be one of the best flavoured Freshwater-fishes in the
East-Indian Archipelago. Its original home is Java, Sumatra, Borneo,
and several other islands; but thence it has been transported to, and
acclimatised in, Penang, Malacca, Mauritius, and even Cayenne. Being
an almost omnivorous fish and tenacious of life, it seems to recommend
itself particularly for acclimatisation in other tropical countries,
and specimens kept in captivity become as tame as carps. It attains the
size of a large turbot. A second, but much smaller, species of this
genus, _O. trichopterus_, is frequently kept in vessels on account of
the exquisite beauty of its varying iridescent metallic tints; like
other fishes of this family it is very pugnacious.

_Trichogaster_, a very common Bengalese fish, differs from
_Osphromenus_ in having the ventral fins reduced to a single long
filament.

   BETTA.--Body compressed, oblong; operculum without spine or
   serrature. Small fixed teeth in the jaws, none on the palate.
   Dorsal fin short, on the middle of the back, without any pungent
   spine; anal fin long. Ventral fin with five soft rays, the outer
   one being produced. Lateral line interrupted or absent.

A species of this genus (_B. pugnax_) is, on account of its
pugnacious habits, reared by the Siamese. Cantor gives the following
account:--“When the fish is in a state of quiet, its dull colours
present nothing remarkable; but if two be brought together, or if
one sees its own image in a looking-glass, the little creature
becomes suddenly excited, the raised fins and the whole body shine
with metallic colours of dazzling beauty, while the projected gill
membrane, waving like a black frill round the throat, adds something
of grotesqueness to the general appearance. In this state it makes
repeated darts at its real or reflected antagonist. But both, when
taken out of each other’s sight, instantly become quiet. This
description was drawn up in 1840, at Singapore, by a gentleman who had
been presented with several by the King of Siam. They were kept in
glasses of water, fed with larvæ of mosquitoes, and had thus lived for
many months. The Siamese are as infatuated with the combats of these
fish as the Malays are with their cock-fights; and stake on the issue
considerable sums, and sometimes their own persons and families. The
license to exhibit fish-fights is farmed, and brings a considerable
annual revenue to the King of Siam. The species abounds in the rivulets
at the foot of the hills of Penang. The inhabitants name it ‘Pla-kat,’
or the ‘Fighting-fish;’ but the kind kept especially for fighting is an
artificial variety cultivated for the purpose.”

MICRACANTHUS.--This genus represents the three last-named genera in
Africa, where it has been recently discovered in tributaries of the
river Ogooué. It seems to differ from the Indian genera chiefly by its
more elongate body, the structure of the fins being scarcely different
(D. 3/7, A. 4/23, V. 1/4).


                    SECOND FAMILY--LUCIOCEPHALIDÆ.

_Body elongate, covered with scales of moderate size. Lateral line
present. Teeth small. Gill-opening wide; pseudobranchiæ none. The
superbranchial organ is formed by two branchial arches, which are
dilated into a membrane. One short dorsal fin; dorsal and anal spines
none; ventrals composed of one spine and five rays. Air-bladder
none._

A small Freshwater-fish (_Luciocephalus pulcher_), from the
East-Indian Archipelago.


         SEVENTEENTH DIVISION--ACANTHOPTERYGII LOPHOTIFORMES.

_Body riband shaped, with the vent near its extremity; a short anal
behind the vent; dorsal fin as long as the body._

Only one species is known of this division or family, _Lophotes
cepedianus_. It is most probably a deep-sea fish, but does not descend
to so great a depth as the _Trachypteridæ_, its bony and soft parts
being well coherent. It is a scarce fish, hitherto found in the
Mediterranean, off Madeira, and in the Sea of Japan; its length is
known to exceed five feet. The head is elevated into a very high crest,
and the dorsal fin commences with an exceedingly strong and long spine
on the head. Silvery, with rose-coloured fins.


           EIGHTEENTH DIVISION--ACANTHOPTERYGII TÆNIIFORMES.

_Body riband shaped; dorsal fin as long as the body; anal absent;
caudal rudimentary, or not in the longitudinal axis of the fish._

  [Illustration: Fig. 237.--Trachypterus tænia.]

The “Ribbon-fishes” are true deep-sea fishes, met with in all parts
of the oceans, generally found when floating dead on the surface, or
thrown ashore by the waves. Their body is like a band, specimens of
from fifteen to twenty feet long being from ten to twelve inches deep,
and about an inch or two broad at their thickest part. The eye is
large and lateral; the mouth small, armed with very feeble teeth; the
head deep and short. A high dorsal fin runs along the whole length of
the back, and is supported by extremely numerous rays; its foremost
portion, on the head, is detached from the rest of the fin, and
composed of very elongate flexible spines. The anal fin is absent. The
caudal fin (if preserved, which is rarely the case, in adult specimens)
has an extra-axial position, being directed upwards like a fan. The
ventrals are thoracic, either composed of several rays or reduced to a
single long filament. The coloration is generally silvery, with rosy
fins.

When these fishes reach the surface of the water the expansion of the
gases within their body has so loosened all parts of their muscular and
bony system, that they can be lifted out of the water with difficulty
only, and nearly always portions of the body and fins are broken and
lost. The bones contain very little bony matter, are very porous, thin
and light. At what depths Ribbon-fishes live is not known; probably
the depths vary for different species; but although none have been
yet obtained by means of the deep-sea dredge, they must be abundant
at the bottom of all oceans, as dead fishes or fragments of them
are frequently obtained. Some writers have supposed from the great
length and narrow shape of these fishes that they have been mistaken
for “Sea-serpents;” but as these monsters of the sea are always
represented by those who have had the good fortune of meeting with them
as remarkably active, it is not likely that harmless Ribbon-fishes,
which are either dying or dead, have been the objects described as
“Sea-serpents.”

  [Illustration: Fig. 238.--Young Trachypterus.]

Young Ribbon-fishes (from two to four inches) are not rarely met with
near the surface; they possess the most extraordinary development of
fin rays observed in the whole class of fishes, some of them being
several times longer than the body, and provided with lappet-like
dilatations. There is no doubt that fishes with such delicate
appendages are bred and live in depths where the water is absolutely
quiet, as a sojourn in the disturbed water of the surface would
deprive them at once of organs which must be of some utility for their
preservation.

Ribbon-fishes are divided into three genera:--

TRACHYPTERUS.--In which the ventral rays are well developed, and
composed of several more or less branched rays. Specimens of this genus
have been taken in the Mediterranean, Atlantic, at Mauritius, and in
the Eastern Pacific. The “Deal-fish” (_T. arcticus_) is often met with
in the North Atlantic, and specimens are generally found after the
equinoctial gales on the coasts of the Orkneys and North Britain.

STYLOPHORUS.--Without ventrals, and with the tail terminating in an
exceedingly long cord-like appendage. Known from one specimen only,
found at the beginning of this century between Cuba and Martinique. It
is eleven inches long, and preserved in the Museum of the Royal College
of Surgeons in London.

_Regalecus._--Each ventral fin is reduced to a long filament, dilated
at the extremity; caudal fin rudimentary or absent. These are the
largest of all Ribbon-fishes, specimens being on record the length of
which exceeded twenty feet. They have been taken in the Mediterranean,
North and South Atlantic, Indian Ocean, and on the coast of New
Zealand. They are frequently called “Kings of the herrings,” from
the erroneous notion that they accompany the shoals of herrings; or
“Oar-fishes,” from their two ventral fins, which have a dilatation at
their extremity not unlike the blade of an oar. One or more species
(_R. banksii_) are sometimes found on the British coasts, but they
are very scarce, not more than sixteen captures having been recorded
between the years 1759 and 1878.


        NINETEENTH DIVISION--ACANTHOPTERYGII NOTACANTHIFORMES.

_Dorsal fin short, composed of short, isolated spines, without a soft
portion. Anal fin very long, anteriorly with many spines; ventrals
abdominal, with more than five soft and several unarticulated rays._

_Notacanthus_ is the most aberrant type of Acanthopterygians. Of
the characteristics of this order the development of spines in the
vertical fins is the only one preserved in the fishes of this genus.
Their body is elongate, covered with very small scales; the snout
protrudes beyond the mouth. Eyes lateral, of moderate size; dentition
feeble. Five species are known from the Arctic Ocean, Mediterranean,
Atlantic, and Southern Pacific. They inhabit considerable depths,
probably from 100 to 400 fathoms, and during the “Challenger”
expedition specimens have been obtained from an alleged depth of 1875
fathoms.


                             SECOND ORDER:

                    ACANTHOPTERYGII PHARYNGOGNATHI.

_Part of the rays of the dorsal, anal, and ventral fins are
non-articulated spines. The lower pharyngeals coalesced. Air-bladder
without pneumatic duct._

  [Illustration: Fig. 239.--Coalescent Pharyngeals of Scarus
  cretensis. _a_, upper; _b_, lower pharyngeals.]


FIRST FAMILY--POMACENTRIDÆ.

_Body short, compressed, covered with ctenoid scales. Dentition
feeble; palate smooth. The lateral line does not extend to the caudal
fin, or is interrupted. One dorsal fin, with the spinous portion as
well developed as the soft, or more. Two, sometimes three, anal spines;
the soft anal similar to the soft dorsal. Ventral fins thoracic, with
one spine and five soft rays. Gills three and a half; pseudobranchiæ
and air-bladder present. Vertebræ, twelve abdominal and fourteen
caudal._

  [Illustration: Fig. 240.--Dascyllus aruanus. Natural size, from
  the Indo-Pacific.]

The fishes of this family are marine; they resemble the Chætodonts
with regard to their mode of life, living chiefly in the neighbourhood
of coral formations. Like them they are beautifully coloured, the
same patterns being sometimes reproduced in members of both families,
proving that the development and distribution of colours is due to
the agencies of climate, of the surroundings and of the habits of
animals. The geographical range of the _Pomacentridæ_ is co-extensive
with that of the Chætodonts, the species being most numerous in
the Indo-Pacific and Tropical Atlantic, a few extending northwards
to the Mediterranean and Japan, southwards to the coasts of South
Australia. They feed chiefly on small marine animals, and such as
have compressed teeth appear to feed on the small Zoophytes covering
the banks, round which these “Coral-fishes” abound. In a fossil state
this family is known from a single genus only, _Odonteus_, from Monte
Bolca, allied to _Heliastes_. The recent genera belonging to this
family are:--_Amphiprion_, _Premnas_, _Dascyllus_, _Lepidozygus_,
_Pomacentrus_, _Glyphidodon_, _Parma_, and _Heliastes_. About 120
species are known.


                        SECOND FAMILY--LABRIDÆ.

_Body oblong or elongate, covered with cycloid scales. The lateral
line extends to the caudal, or is interrupted. One dorsal fin, with the
spinous portion as well developed as, or more than, the soft. The soft
anal similar to the soft dorsal. Ventral fins thoracic, with one spine
and five soft rays. Palate without teeth. Branchiostegals five or six;
gills three and a half; pseudobranchiæ and air-bladder present. Pyloric
appendages none; stomach without cæcal sac._

  [Illustration: Fig. 241.--Lips of a Wrasse, _Labrus
  festivus_.]

The “Wrasses” are a large family of littoral fishes, very abundant in
the temperate and tropical zones, but becoming scarcer towards the
Arctic and Antarctic circles, where they disappear entirely. Many of
them are readily recognised by their thick lips, which are sometimes
internally folded, a peculiarity which has given to them the German
term of “Lip-fishes.” They feed chiefly on mollusks and crustaceans,
their dentition being admirably adapted for crushing hard substances.
Many species have a strong curved tooth at the posterior extremity of
the intermaxillary, for the purpose of pressing a shell against the
lateral and front teeth by which it is crushed. Other Wrasses feed on
corals, others on zoophytes; a few are herbivorous. In all Wrasses
the upper pharyngeal bones seem to be jointed to the basi-occipital;
but whilst in _Labrus_ the basi-occipital is raised on each side
into a large flattish condyle, fitting into a concavity of the upper
pharyngeals, in _Scarus_ the mode of articulation is reversed,
the basi-occipital having a pair of long grooves, in which the oblong
condyles of the upper pharyngeals slide forwards and backwards.
Beautiful colours prevail in this family, permanent pigmentary colours
as well as passing iridescent reflections of the scales. Some species
remain very small, others grow to a weight of fifty pounds. The larger
kinds especially are prized as food, the smaller less so.

Remains of Labridæ, recognised by their united pharyngeals, which bear
molar-like teeth, are not scarce in tertiary formations of France,
Germany, Italy, and England. Such remains from Monte Bolca and the
Swiss Molasse have been referred to the genus _Labrus_. Others,
_Nummopalatus_ and _Phyllodus_, are allied, but cannot be assigned,
to one of the recent genera; the latter genus is first represented in
cretaceous formations of Germany. Another genus, _Taurinichthys_, from
the Miocene of France, represents the _Odacina_ of the living fauna.
_Egertonia_, from the Isle of Sheppey, differs so much from all recent
Labroid genera that its pertinence to this family appears doubtful.

   [See _J. Cocchi_, Monografia dei Pharyngodopilidæ, 1866; and _E.
   Sauvage_, Sur le genre Nummopalatus, in Bull. Soc. Geol. France,
   1875.]

   LABRUS.--Body compressed, oblong, covered with scales of
   moderate size, in more than forty transverse series; snout more
   or less pointed; imbricate scales on the cheeks and opercles;
   none or only a few on the interoperculum. Teeth in the jaws
   conical, in a single series. Dorsal spines numerous, thirteen
   or twenty-one, none of which are prolonged; anal spines three.
   Lateral line not interrupted.

Young “Wrasses” differ from mature specimens in having the præoperculum
serrated. The headquarters of this genus are the Mediterranean, whence
it ranges, gradually diminishing towards the north, along all the
shores of Europe. Nine species are known; British are the “Ballan
Wrasse” (_L. maculatus_), and the “Striped or Red Wrasse” or “Cook”
(_L. mixtus_). The two sexes of the latter species are very differently
coloured; the male being generally ornamented with blue streaks, or a
blackish band along the body, whilst the female has two or three large
black blotches across the back of the tail.

   CRENILABRUS are Labrus with serrated præoperculum; the number of
   their dorsal spines varies from thirteen to eighteen, and the
   scales are arranged in less than forty transverse series.

The range of this genus is co-extensive with _Labrus_. _C. melops_, the
“Gold-sinny,” or “Cork-wing,” is common on the British coasts.

   TAUTOGA.--Body compressed, oblong, covered with small scales;
   scales on the cheek rudimentary, opercles naked. Teeth in the
   jaws conical, in double series; no posterior canine tooth.
   Dorsal spines seventeen, anal spines three. Lateral line not
   interrupted.

The “Tautog,” or “Black-fish,” is common on the Atlantic coasts of
temperate North America, and much esteemed as food.

   CTENOLABRUS.--Body oblong, covered with scales of moderate size;
   imbricate scales on the cheeks and opercles. Teeth in the jaws
   in a band, with an outer series of stronger conical teeth; no
   posterior canine tooth. Dorsal spines from sixteen to eighteen;
   anal spines three. Lateral line not interrupted.

Four species, from the Mediterranean and the temperate parts of the
North Atlantic, _Ct. rupestris_ being common on the British, and
_Ct. burgall_ on the North American coasts.

   ACANTHOLABRUS.--A Wrasse with five or six anal spines, and with
   the teeth in a band.

From the Mediterranean and British coasts (_A. palloni_).

   CENTROLABRUS.--Wrasses with four or five anal spines, and with
   the teeth in a single series.

Two species are known from Madeira and the Canary Islands, and one from
northern Europe and Greenland. The latter is scarce on the British
coasts, but bears a distinct name on the south coast, where it is
called “Rock-cook.”

LACHNOLAEMUS from the West Indies, and MALACOPTERUS from Juan
Fernandez, are Labroids, closely allied to the preceding North Atlantic
genera.

   COSSYPHUS.--Body compressed, oblong, with scales of moderate
   size; snout more or less pointed; imbricate scales on the cheeks
   and opercles; basal portion of the vertical fins scaly. Lateral
   line not interrupted. Teeth in the jaws in a single series; four
   canine teeth in each jaw anteriorly; a posterior canine tooth.
   Formula of the fins: D. 12/9–11, A. 3/12.

Twenty species are known from the tropical zone and coasts adjoining
it; some, like _G. gouldii_ from Tasmania, attain a length of
three or four feet.

   CHILINUS.--Body compressed, oblong, covered with large scales;
   lateral line interrupted; cheeks with two series of scales;
   præoperculum entire; teeth in a single series, two canines in
   each jaw; no posterior canine tooth; lower jaw not produced
   backwards. Dorsal spines subequal in length; formula of the
   fins: D. 9–10/10–9, A. 3/8.

Common in the tropical Indo-Pacific, whence more than twenty species
are known. Hybrids between the different species of this genus are not
uncommon.

   EPIBULUS.--Closely allied to the preceding genus, but with
   a very protractile mouth, the ascending branches of the
   intermaxillaries, the mandibles, and the tympanic being much
   prolonged.

This fish (_E. insidiator_) is said to seize marine animals by
suddenly thrusting out its mouth and engulphing those that come within
the reach of the elongated tube. It attains a length of twelve inches,
is common in the tropical Indo-Pacific, and varies much in coloration.

   ANAMPSES.--Distinguished by its singular dentition, the
   two front teeth of each jaw being prominent, directed forwards,
   compressed, with cutting edge. D. 9/12, A. 3/12.

Beautifully coloured fishes from the tropical Indo-Pacific. Ten species.

   PLATYGLOSSUS.--Scales in thirty or less transverse series;
   lateral line not interrupted. A posterior canine tooth. Dorsal
   spines nine.

Small beautifully coloured Coral-fishes, abundant in the equatorial
zone and the coasts adjoining it. Some eighty species are known
(inclusive of the allied genera _Stethojulis_, _Leptojulis_, and
_Pseudojulis_).

   NOVACULA.--Body strongly compressed, oblong, covered with
   scales of moderate size; head compressed, elevated, obtuse,
   with the supero-anterior profile more or less parabolic; head
   nearly entirely naked. Lateral line interrupted. No posterior
   canine tooth. D. 9/12, A. 3/12; the two anterior dorsal spines
   sometimes remote or separate from the others.

Twenty-six species are known from the tropical zone, and the warmer
parts of the temperate zones. They are readily recognised by their
compressed, knife-shaped body, and peculiar physiognomy; they scarcely
exceed a length of twelve inches.

   JULIS.--Scales of moderate size; lateral line not interrupted.
   Head entirely naked. Snout of moderate extent, not produced; no
   posterior canine tooth. Dorsal spines ten.

Co-extensive with _Platyglossus_ in their geographical distribution,
and of like beautiful coloration and similar habits. Some of the most
common fishes of the Indo-Pacific, as _J. lunaris_, _trilobata_, and
_dorsalis_, belong to this genus.

   CORIS.--Scales small, in fifty or more transverse series;
   lateral line not interrupted. Head entirely naked. Dorsal spines
   nine.

Twenty-three species, distributed like _Platyglossus_; two reach the
south coast of England, _Coris julis_ and _C. giofredi_, said to be
male and female of the same species. Some belong to the most gorgeously
coloured kinds of the whole class of fishes.

Genera allied to the preceding Labroids are--_Choerops_, _Xiphochilus_,
_Semicossyphus_, _Trochocopus_, _Decodon_, _Pteragogus_, _Clepticus_,
_Labrichthys_, _Labroides_, _Duymæria_, _Cirrhilabrus_, _Doratonotus_,
_Pseudochilinus_, _Hemigymnus_, _Gomphosus_, _Cheilio_, and _Cymolutes_.

   PSEUDODAX.--Scales of moderate size; lateral line continuous;
   cheeks and opercles scaly. Each jaw armed with two pairs of
   broad incisors, and with a cutting lateral edge; teeth of the
   lower pharyngeal confluent, pavement-like. Dorsal spines eleven.

One species (_P. moluccensis_) from the East Indian Archipelago.

   SCARUS.--Jaws forming a sharp beak, the teeth being soldered
   together. The lower jaw projecting beyond the upper. A single
   series of scales on the cheek; dorsal spines stiff, pungent; the
   upper lip double in its whole circuit. The dentigerous plate of
   the lower pharyngeal is broader than long.

The fishes of this genus, and the three succeeding, are known by the
name of “Parrot-wrasses.” Of _Scarus_ one species (_S. cretensis_)
occurs in the Mediterranean, and nine others in the tropical Atlantic.
The first was held in high repute by the ancients, and Aristotle has
several passages respecting its rumination. It was most plentiful and
of the best quality in the Carpathian Sea, between Crete and Asia
Minor, but was not unknown even in early times on the Italian coasts,
though Columella says that it seldom passed beyond Sicily in his day.
But in the reign of Claudius, according to Pliny, Optatus Elipentius
brought it from the Troad, and introduced it into the sea between
Ostium and Campagna. For five years all that were caught in the nets
were thrown into the sea again, and from that time it was an abundant
fish in that locality. In the time of Pliny it was considered to be
the first of fishes _(Nunc Scaro datur principatus_); and the expense
incurred by Elipentius was justified, in the opinion of the Roman
gourmands, by the extreme delicacy of the fish. It was a fish, said
the poets, whose very excrements the gods themselves were unwilling
to reject. Its flesh was tender, agreeable, sweet, easy of digestion,
and quickly assimilated; yet if it happened to have eaten an Aplysia,
it produced violent diarrhœa. In short, there is no fish of which so
much has been said by ancient writers. In the present day the Scarus of
the Archipelago is considered to be a fish of exquisite flavour; and
the Greeks still name it _Scaro_, and eat it with a sauce made of its
liver and intestines. It feeds on fucus; and Valenciennes thinks that
the necessity for masticating its vegetable diet thoroughly, and the
working of it with that intent backwards and forwards in the mouth,
may have given rise to the notion of its being a ruminant; and it is
certain that its aliment is very finely divided when it reaches the
stomach.

  [Illustration: Fig. 242.--Scarichthys auritus.]

   SCARICHTHYS.--Differing from _Scarus_ only in having flexible
   dorsal spines.

Two species from the Indo-Pacific.

   CALLYODON.--Differing from _Scarichthys_ in having the upper lip
   double posteriorly only.

Nine species from the tropical zone.

   PSEUDOSCARUS.--Jaws forming a strong beak, the teeth being
   soldered together. The upper jaw projecting beyond the lower.
   Two or more series of scales on the cheek. The dentigerous plate
   of the lower pharyngeal longer than broad.

This tropical genus contains by far the greatest number of Scaroid
Wrasses, some seventy species being known, and a still greater number
of names being introduced into the various Ichthyological works. They
are beautifully coloured, but the colours change with age, and vary
in an extraordinary degree in the same species. They rapidly fade
after death, so that it is almost impossible to recognise in preserved
specimens the species described from living individuals. Many attain
to a rather large size, upwards of three feet in length. The majority
are eaten, but some acquire poisonous properties from their food, which
consists either of corals or of fucus.

   ODAX.--The edge of each jaw is sharp, without distinct teeth.
   The dentigerous plate of the lower pharyngeal triangular, much
   broader than long. Cheeks and opercles scaly; scales of the body
   small or rather small; lateral line continuous. Snout conical.
   Dorsal spines rather numerous, flexible.

  [Illustration: Fig. 243.--Odax radiatus.]

Six species from the coasts of Australia and New Zealand. Small. The
species figured (_O. radiatus_) is from Western Australia.

   CORIDODAX.--Jaws as in _Odax_, head naked. Scales of the body
   small; lateral line continuous. Snout of moderate extent. Dorsal
   spines numerous, flexible.

The “Butter-fish,” or “Kelp-fish” of the colonists of New Zealand
(_C. pullus_), is prized as food, and attains to a weight of four
or five pounds. It feeds on zoophytes, scraping them from the surface
of the kelp, with its curiously formed teeth. Its bones are green, like
those of _Belone_.

OLISTHEROPS, from King George’s Sound, has scales of moderate size, but
agrees otherwise with _Coridodax_.

   SIPHONOGNATHUS.--Head and body very elongate, snout long, as in
   _Fistularia_; upper jaw terminating in a long, pointed, skinny
   appendage; opercles and cheeks scaly; scales of moderate size;
   lateral line continuous. Dorsal spines numerous, flexible. Jaws
   as in _Odax_; the dentigerous plate of the lower pharyngeal very
   narrow.

_S. argyrophanes_, from King George’s Sound, is the most aberrant
type of Wrasses, whose principal characters are retained, but united
with a form of the body which resembles that of a Pipe-fish.


                      THIRD FAMILY--EMBIOTOCIDÆ.

_Body compressed, elevated or oblong, covered with cycloid scales;
lateral line continuous. One dorsal fin, with a spinous portion, and
with a scaly sheath along the base, which is separated by a groove from
the other scales; anal with three spines and numerous rays; ventral
fins thoracic, with one spine and five rays. Small teeth in the jaws,
none on the palate. Pseudobranchiæ present. Stomach siphonal, pyloric
appendages none. Viviparous._

Marine Fishes characteristic of the fauna of the temperate North
Pacific, the majority living on the American side, and only a few
on the Asiatic. All are viviparous (see Fig. 70, p. 159). Agassiz
describes the development of the embryoes as a normal ovarian
gestation, the sac containing the young not being the oviduct but
the ovarian sheath, which fulfils the functions of the ovary. This
organ presents two modes of arrangement: in one there is a series of
triangular membranous flaps communicating with each other, between
which the young are arranged, mostly longitudinally, the head of one
to the tail of another, but sometimes with the bodies curved, to the
number of eighteen or twenty; in the other, the cavity is divided by
three membranes converging to a point, into four compartments, not
communicating with each other except towards the genital opening, the
young being arranged in the same longitudinal manner. The proportionate
size of the young is very remarkable. In a female specimen 10½ inches
long, and 4½ inches high, the young were nearly 3 inches long and 1
inch high. Seventeen species are known, the majority of which belong to
_Ditrema_, and one to _Hysterocarpus_. They do not attain to
a large size, varying from three-quarters to three pounds in weight.


                       FOURTH FAMILY--CHROMIDES.

_Body elevated, oblong or elongate, scaly, the scales being generally
ctenoid. Lateral line interrupted or nearly so. One dorsal fin, with a
spinous portion; three or more anal spines; the soft anal similar to
the soft dorsal. Ventral fins thoracic, with one spine and five rays.
Teeth in the jaws small, palate smooth. Pseudobranchiæ none. Stomach
coecal; pyloric appendages none._

Freshwater-fishes of rather small size from the tropical parts of
Africa and America; one genus from Western India. The species with
lobate teeth, and with many circumvolutions of the intestines, are
herbivorous, the other carnivorous.

   ETROPLUS.--Body compressed, elevated, covered with ctenoid
   scales of moderate size. Lateral line indistinct. Dorsal and
   anal spines numerous. Teeth compressed, lobate, in one or
   two series. Anterior prominences of the branchial arches not
   numerous, short, conical, hard. Dorsal fin not scaly.

Two species from Ceylon and Southern India.

   CHROMIS.--Body compressed, oblong, covered with cycloid
   scales of moderate size. Dorsal spines numerous, anal spines
   three. Teeth compressed, more or less lobate, in one series.
   Anterior prominences of the branchial arches short, thin,
   lamelliform, non-serrated. Dorsal fin not scaly.

Some twenty species are known from the fresh waters of Africa and
Palestine; the most celebrated is the “Bulti,” or “Bolty,” of the Nile,
one of the few well-flavoured fishes of that river; it grows to the
length of twenty inches. Two or three species of this genus occur in
the Jordan and Lake of Galilee.

  [Illustration: Fig. 244.--_Chromis andreæ_, from the Lake of
  Galilee.]

   HEMICHROMIS, differing from _Chromis_ in having conical teeth in
   one or two series.

Ten species, the range of which is co-extensive with that of _Chromis_.
One species, _H. sacra_, is abundant in the Lake of Galilee.

   PARETROPLUS, differing from _Hemichromis_ in having nine anal
   spines.

One species from Madagascar.

   ACARA.--Body compressed, oblong, covered with ctenoid scales
   of moderate size. Dorsal spines numerous, anal spines three or
   four; base of the soft dorsal nearly uncovered by scales. Teeth
   in a band, small, conical. Anterior prominences of the first
   branchial arch very short tubercles.

Some twenty species are known from the fresh waters of Tropical
America, _A. bimaculata_ being one of the most common fishes of
that region. All are very small.

   HEROS.--Differing from _Acara_ in having more than four anal
   spines.

Some fifty species are known from the fresh waters of Tropical America,
especially Central America, where almost every large lake or river is
tenanted by one or more peculiar species. They are of rather small
size, rarely exceeding a length of twelve inches.

  [Illustration: Fig. 245.--_Heros salvini_, from Central
  America.]

Genera allied to _Heros_, and likewise from Tropical America, are
_Neetroplus_, _Mesonauta_, _Petenia_, _Uaru_, and _Hygrogonus_.

   CICHLA.--Form of the body perch-like. Scales small; the spinous
   and soft portions of the dorsal fin of nearly equal extent,
   and separated by a notch; anal spines three. Each jaw with a
   broad band of villiform teeth. The outer branchial arch with
   lanceolate crenulated prominences along its concave side. Dorsal
   and anal fins scaly.

Four species from Brazil, Guyana, and Peru.

   CRENICICHLA.--Body low, sub-cylindrical; scales small or rather
   small. The spinous portion of the dorsal is much more developed
   than the soft, both being continuous, and not separated by a
   notch; anal spines three. Præopercular margin serrated. Each
   jaw with a band of conical teeth. The outer branchial arch with
   short tubercles. Dorsal and anal fins naked.

Ten species from Brazil and Guyana.

The following genera complete the list of South American Chromides:
_Chætobranchus_, _Mesops_, _Satanoperca_, _Geophagus_, _Symphysodon_,
and _Pterophyllum_.


                       THIRD ORDER--ANACANTHINI.

_Vertical and ventral fins without spinous rays. The ventral fins,
if present, are jugular or thoracic. Air-bladder, if present, without
pneumatic duct._

These characters are common to all the members of this order, with
the exception of a freshwater-fish from Tasmania and South Australia
(_Gadopsis_), which has the anterior portion of the dorsal and anal
fins formed of spines.


                 FIRST DIVISION--ANACANTHINI GADOIDEI.

_Head and body symmetrically formed._


                        FIRST FAMILY--LYCODIDÆ.

_Vertical fins confluent. Ventral fin, if present, small, attached to
the humeral arch, jugular. Gill-opening narrow, the gill-membrane being
attached to the isthmus._

Marine littoral fishes of small size, resembling Blennies, chiefly
represented in high latitudes, but a few living within the tropical
zone.

   LYCODES.--Body elongate, covered with minute scales imbedded in
   the skin, or naked; lateral line more or less indistinct. Eye
   of moderate size. Ventral small, short, rudimentary, jugular,
   composed of several rays. Upper jaw overlapping the lower.
   Conical teeth in the jaws, on the vomer, and on the palatine
   bones. Barbel none. Five or six branchiostegals; gill-opening
   narrow, the gill-membranes being attached to the isthmus.
   Pseudobranchiæ present. Air-bladder none. Pyloric appendages
   two, or rudimentary, or entirely absent. No prominent anal
   papilla.

  [Illustration: Fig. 246.--Lycodes mucosus, from Northumberland
  Sound.]

Nine species are known from the Arctic Ocean, four from the southern
extremity of the American continent.

   GYMNELIS.--Body elongate, naked. Eye of moderate size or rather
   small. Ventrals none. Vent situated at some distance backwards
   from the head. Small conical teeth in the jaws, on the vomer
   and palatine bones. Jaws equal anteriorly. Barbel none. Six
   branchiostegals; gill-opening narrow, the gill membranes being
   attached to the isthmus. Pseudobranchiæ present; air-bladder
   none. Pyloric appendages two; no prominent anal papilla.

  [Illustration: Fig. 247.--Gymnelis viridis.]

One species (_G. viridis_) from Greenland, the other (_G. pictus_) from
the Straits of Magelhæn.

The other genera belonging to this family are _Uronectes_ from Baffin’s
Bay, _Microdesmus_ from Panama, _Blennodesmus_ from the coast of
North-Eastern Australia, and _Maynea_ from the Straits of Magelhæn.


                        SECOND FAMILY--GADIDÆ.

_Body more or less elongate, covered with small smooth scales. One,
two, or three dorsal fins, occupying nearly the whole of the back; rays
of the posterior dorsal well developed; one or two anal fins. Caudal
free from dorsal and anal, or, if they are united, the dorsal with a
separate anterior portion. Ventrals jugular, composed of several rays,
or, if they are reduced to a filament, the dorsal is divided into two.
Gill-opening wide; the gill-membranes generally not attached to the
isthmus. Pseudobranchiæ none, or glandular, rudimentary. An air-bladder
and pyloric appendages generally present._

The family of “Cod-fishes” consists partly of littoral and surface
species (and they form the majority), partly of deep-sea forms. The
former are almost entirely confined to the temperate zones, extending
beyond the Arctic Circle; the latter have, as deep-sea fishes
generally, a much wider range, and hitherto have been found chiefly at
considerable depths of rather low latitudes. Only two or three species
inhabit fresh waters. They form one of the most important articles of
food and subsistence to the fishermen in Europe and North America, and
to whole tribes bordering upon the Arctic Ocean.

Fossil remains are scarce. _Nemopteryx_ and _Palæogadus_ have been
described from the schists of Glaris, a formation believed to have been
the bottom of a very deep sea. In the clay of Sheppey species occur
allied to _Gadus_, _Merluccius_, and _Phycis_; others, not readily
determinable, have been found at Licata in Sicily (Miocene).

   GADUS.--Body moderately elongate, covered with small scales.
   A separate caudal, three dorsal, and two anal fins; ventrals
   narrow, composed of six or more rays. Teeth in the upper jaw in
   a narrow band; vomerine teeth; none on the palatines.

Arctic and temperate zones of the Northern Hemisphere. Eighteen species
are known, of which the following are the most important:--

_Gadus morrhua_, the common “Cod-fish”--in German called “Kabeljau”
when fresh and old, “Dorsch” when young and fresh, “Stock-fish” when
dried, “Labberdan” when salted--measures from two to four feet, and
attains to a weight of one hundred pounds. On the British coasts and
in the German Ocean it is generally of a greenish or brownish-olive
colour, with numerous yellowish or brown spots. Farther northwards
darker-coloured specimens, frequently without any spots, predominate;
and on the Greenland, Iceland, and North Scandinavian coasts the Cod
have often a large irregular black blotch on the side. The Cod-fish
occurs between 50° and 75° lat. N., in great profusion, to a depth of
120 fathoms, but is not found nearer the Equator than 40° lat. Close
to the coast it is met with singly all the year round, but towards
the spawning-time it approaches the shore in numbers, which happens
in January in England and not before May on the American coasts. The
English resorted to the cod-fisheries of Iceland before the year
1415, but since the sixteenth century most vessels go to the banks of
Newfoundland, and almost all the preserved Cod consumed during Lent in
the various continental countries is imported from across the Atlantic.
At one time the Newfoundland cod-fishery rivalled in importance the
whale-fishery and the fur trade of North America. Cod-liver oil is
prepared from the liver on the Norwegian coast, but also other species
of this genus contribute to this most important drug.

_Gadus tomcodus_ abundantly occurs on the American coasts; it remains
within smaller dimensions than the common Cod-fish. _Gadus æglefinus_,
the “Haddock” (“Schell-fisch” of the Germans, “Hadot” of the French),
is distinguished by a black lateral line and a blackish spot above
the pectoral fin. It attains to a length of three feet in the higher
latitudes, but remains smaller on more southern coasts; like the Cod
it extends across the Atlantic. The largest specimens are taken on
the British coast in winter, because at that time they leave the deep
water to spawn on the coast. _Gadus merlangus_, the “Whiting,” with a
black spot in the axil of the pectoral fin. _Gadus luscus_, the “Bib,”
“Pout,” or “Whiting-pout,” with cross-bands during life, and with a
black axillary spot, rarely exceeding a weight of five pounds. _Gadus
fabricii_, a small species, but occurring in incredible numbers on
the shores near the Arctic circle, and ranging to 80° lat. N. _Gadus
pollachius_, the “Pollack,” without a barbel at the chin, and with the
lower jaw projecting beyond the upper. _Gadus virens_, the “Coal-fish,”
valuable on account of its size and abundance, and therefore preserved
for export like the Cod.

The fishes of the genus _Gadus_ are bathymetrically succeeded by
several genera, as _Gadiculus_, _Mora_, and _Strinsia_; however these
do not descend to sufficiently great depths to be included into the
deep-sea Fauna; the two following are true deep-sea fishes.

   HALARGYREUS.--Body elongate, covered with small scales. Two
   dorsal and two anal fins; ventrals composed of several rays.
   Jaws with a band of minute villiform teeth; vomer and palatines
   toothless. No barbel.

The single species known, _H. johnsonii_, proves to be a deep-sea fish
by its organisation as well as geographical distribution. Originally
known from a single specimen, which was obtained at Madeira, it has
since been found off the coast of New Zealand. There is no doubt that
it will be discovered also in intermediate seas.

   MELANONUS.--Head and body rather compressed, covered with
   cycloid scales of moderate size, and terminating in a long
   tapering tail, without caudal. Eye of moderate size. Villiform
   teeth in the jaws, on the vomer and palatine bones. Barbel
   none. A short anterior dorsal, the second extending to the end
   of the tail, and the anal being of similar length. Ventrals
   composed of several rays. Bones soft and flexible.

This is one of the discoveries made during the expedition of the
“Challenger.” The single specimen obtained is of a deep-black colour,
and was dredged up at a depth of 1975 fathoms in the Antarctic Ocean.

   MERLUCCIUS.--Body elongate, covered with very small scales. A
   separate caudal; two dorsal fins and one anal; ventrals well
   developed, composed of seven rays. Teeth in the jaws and on the
   vomer rather strong, in double or triple series. No barbel.

Two species are known of this genus, widely separated in their
distribution. The European species, _M. vulgaris_, the “Hake,” is found
on both sides of the Atlantic, and grows to a length of four feet. It
is caught in great numbers, and preserved as “Stock-fish.” The second
species _M. gayi_, is common in the Straits of Magelhæn and on the
coast of Chili, less so in New Zealand.

The vertebral column of this genus shows a singular modification of
the apophyses. The neural spines of all the abdominal vertebræ are
extremely strong, dilated, wedged into one another. The parapophyses
of the third to sixth vertebræ are slender, styliform, whilst those of
all the following abdominal vertebræ are very long and broad, convex on
the upper and concave on the lower surface; the two or three anterior
pairs are, as it were, inflated. The whole forms a strong roof for the
air-bladder, reminding us of a similar structure in _Kurtus_.

   PSEUDOPHYCIS.--Body of moderate length, covered with rather
   small scales. A separate caudal, two dorsals, and one anal;
   ventral fins very narrow and styliform, but composed of several
   rays. Jaws with a band of small teeth; vomer and palatines
   toothless. Chin with a barbel.

Two species, of which _Ps. bachus_ is common on the coast of New
Zealand.

Allied genera are _Lotella_, _Physiculus_, _Uraleptus_, and _Læmonema_,
from moderate depths, obtained chiefly off Madeira and the Southern
Temperate Zone.

  [Illustration: Fig. 248.--Pseudophycis bachus.]

   PHYCIS.--Body of moderate length, covered with small scales.
   Fins more or less enveloped in loose skin. A separate caudal;
   two dorsal fins and one anal; the anterior dorsal composed of
   from eight to ten rays; ventrals reduced to a single long ray,
   bifid at its end. Small teeth in the jaws and on the vomer;
   palatine bones toothless. Chin with a barbel.

Six species from the temperate parts of the North Atlantic and the
Mediterranean, one, _Ph. blennioides_, is occasionally found on
the British coast.

   HALOPORPHYRUS.--Body elongate, covered with small scales. A
   separate caudal, two dorsal fins, and one anal; the first dorsal
   with four rays; ventrals narrow, composed of six rays. Jaws and
   vomer with villiform teeth; palatine bones toothless. Chin with
   a barbel.

A small genus of deep-sea fishes, of which three species are known.
They offer a striking instance of the extraordinary distribution of
deep-sea fishes; _H. lepidion_ occurs in from 100 to 600 fathoms
in the Mediterranean and the neighbouring parts of the Atlantic, off
the coast of Japan, and various parts of the South Atlantic; _H.
australis_ in from 55 to 70 fathoms in the Straits of Magelhæn; and
finally _H. rostratus_ in from 600 to 1375 fathoms, midway between
the Cape of Good Hope and Kerguelen’s Land, and in the South Atlantic.

   LOTA.--Body elongate, covered with very small scales. A separate
   caudal, two dorsal fins, and one anal; ventrals narrow, composed
   of six rays. Villiform teeth in the jaws and on the vomer; none
   on the palatines. The first dorsal with from ten to thirteen
   well-developed rays. Chin with a barbel.

The “Burbot,” or “Eel-pout” (_L. vulgaris_, Fig. 8, p. 43), is
a Freshwater-fish which never enters salt water. It is locally
distributed in Central and Northern Europe and North America; it is one
of the best Freshwater-fishes, and exceeds a length of three feet.

   MOLVA.--Differs from Lota in having several large teeth in the
   lower jaw and on the vomer.

The “Ling” (_M. vulgaris_) is a very valuable species, common on the
northern coasts of Europe, Iceland, and Greenland; and generally found
from three to four feet long. The larger number of the specimens caught
are cured and dried.

   MOTELLA.--Body elongate, covered with minute scales. A separate
   caudal. Two dorsal fins, the anterior of which is reduced to a
   narrow rayed fringe, more or less concealed in a longitudinal
   groove; the first ray is prolonged. One anal fin. Ventrals
   composed of from five to seven rays. A band of teeth in the jaws
   and on the vomer.

Eight species of “Rocklings” are known from the coasts of Europe,
Iceland, Greenland, Japan, the Cape of Good Hope, and New Zealand.
They are of small size, and chiefly distinguished by the number of
their barbels. British are the Five-bearded Rockling (_M. mustela_),
the Three-bearded Rocklings (_M. tricirrhata_, _macrophthalma_,
and _maculata_), and the Four-bearded Rockling (_M. cimbria_). _M.
macrophthalma_ comes from a depth of from 80 to 180 fathoms. The young
are known as “Mackerel Midge” (_Couchia_), and sometimes met with in
large numbers at some distance from the coast.

   RANICEPS.--Head large, broad, and depressed; body of moderate
   length, covered with minute scales. A separate caudal. Two
   dorsal fins, the anterior of which is very short, rudimentary.
   One anal fin. Ventrals composed of six rays. Cardlike teeth in
   the jaws and on the vomer.

The “Trifurcated Hake,” _R. trifurcus_, not uncommon on the coasts
of Northern Europe.

   BREGMACEROS.--Body fusiform, compressed posteriorly, covered
   with cycloid scales of moderate size. Two dorsal fins; the
   anterior reduced to a single long ray on the occiput; the second
   and the anal much depressed in the middle; ventrals very long,
   composed of five rays. Teeth small.

  [Illustration: Fig. 249.--Bregmaceros macclellandii.]

A dwarf Gadoid, the only one found at the surface between the Tropics.
_B. macclellandii_ scarcely exceeds three inches in length, is not
uncommon in the Indian Ocean, and has found its way to New Zealand;
specimens have been picked up in mid-ocean.

   MURÆNOLEPIS.--Body covered with lanceolate epidermoid
   productions, intersecting each other at right angles like those
   of a Freshwater-eel. Vertical fins confluent, no caudal being
   discernible; an anterior dorsal fin is represented by a single
   filamentous ray; ventral fins narrow, composed of several rays.
   A barbel. Jaws with a band of villiform teeth; palate toothless.

One species (_M. marmoratus_) from Kerguelen’s Land.

   CHIASMODUS.--Body naked; stomach and abdomen distensible. Two
   dorsal fins and one anal; a separate caudal; ventral fins rather
   narrow, with several rays. Upper and lower jaws with two series
   of large pointed teeth, some of the anterior being very large
   and movable; teeth on the palatine bones, but none on the vomer.
   Chin without barbel.

This Gadoid (_Ch. niger_, Fig. 111, p. 311), inhabits great depths in
the Atlantic (to 1500 fathoms). The specimen figured was taken with a
large Scopeloid in its stomach.

   BROSMIUS.--Body moderately elongate, covered with very small
   scales. A separate caudal, one dorsal, and one anal; ventrals
   narrow, composed of five rays. Vomerine and palatine teeth. A
   barbel.

The “Torsk” (_B. brosme_) is confined to the northern parts of the
temperate zone, and probably extends to the arctic circle.


                       THIRD FAMILY--OPHIDIIDÆ.

_Body more or less elongate, naked, or scaly. Vertical fins generally
united; no separate anterior dorsal or anal; dorsal occupying the
greater portion of the back. Ventral fins rudimentary or absent,
jugular. Gill-openings wide, the gill-membranes not attached to the
isthmus._

Marine fishes (with the exception of _Lucifuga_), partly littoral,
partly bathybial. They may be divided into five groups.

I. _Ventral fins present, attached to the humeral arch_: BROTULINA.

   BROTULA.--Body elongate, covered with minute scales. Eye of
   moderate size. Each ventral reduced to a single filament,
   sometimes bifid at its extremity. Teeth villiform; snout with
   barbels. One pyloric appendage.

Five species of small size from the Tropical Atlantic and Indian Ocean.

  [Illustration: Fig. 250.--Lucifuga dentata, from caves in Cuba.]

_Lucifuga_ are _Brotula_ organised for a subterranean life. The eye
is absent, or quite rudimentary, and covered by the skin; the barbels
of Brotula are replaced by numerous minute ciliæ or tubercles. They
inhabit the subterranean waters of caves in Cuba, and never come to the
light.

   BATHYNECTES.--Body produced into a long tapering tail, without
   caudal. Mouth very wide, villiform teeth in the jaws, on the
   vomer and palatine bones. Barbel none. Ventral fins reduced to
   simple or bifid filaments, placed close together, and near to
   the humeral symphysis. Gill-membranes not united; gill-laminæ
   remarkably short. Bones of the head soft and cavernous;
   operculum with a very feeble spine above.

Deep-sea fishes, inhabiting depths varying from 1000 to 2500 fathoms.
Three species are known, the largest specimen obtained being seventeen
inches long.

  [Illustration: Fig. 251.--Acanthonus armatus.]

   ACANTHONUS.--Head large and thick, armed in front and on the
   opercles with strong spines; trunk very short, the vent being
   below the pectoral; tail thin, strongly compressed, tapering,
   without caudal. Eye small. Mouth very wide; villiform teeth
   in the jaws, on the vomer and palatine bones. Barbel none.
   Ventrals reduced to simple filaments placed close together on
   the humeral symphysis. Scales extremely small. Bones of the head
   soft.

Only two specimens, thirteen inches long, of this remarkable deep-sea
form have been obtained, at a depth of 1075 fathoms, in the Indian
Ocean.

   TYPHLONUS.--Head large, compressed, with most of the bones in
   a cartilaginous condition; the superficial bones with large
   muciferous cavities, not armed. Snout a thick protuberance
   projecting beyond the mouth, which is rather small and inferior.
   Trunk very short, the vent being below the pectoral; tail thin,
   strongly compressed, tapering, without separate caudal. Eye
   externally not visible. Villiform teeth in the jaws, on the
   vomer and palatine bones. Barbel none. Scales thin, deciduous,
   small.

Also of this deep-sea fish two specimens only are known, 10 inches
long, from a depth of 2200 fathoms in the Western Pacific.

   APHYONUS.--Head, body, and tapering tail strongly compressed,
   enveloped in a thin, scaleless, loose skin. Vent far behind
   the pectoral. Snout swollen, projecting beyond the wide
   mouth. No teeth in the upper jaw, small ones in the lower. No
   externally visible eye. Barbel none. Head covered with a system
   of wide muciferous channels, the dermal bones being almost
   membranaceous, whilst the others are in a semi-cartilaginous
   condition. Notochord persistent, but with a superficial
   indication of vertebral segments.

  [Illustration: Fig. 252.--Aphyonus gelatinosus.]

One specimen only of this most remarkable form is known; it is 5½
inches long, and was obtained at a depth of 1400 fathoms south of New
Guinea.

Of the remaining genera belonging to this group, _Brotulophis_,
_Halidesmus_, _Dinematichthys_, and _Bythites_ are surface forms;
_Sirembo_ and _Pteridium_ inhabit moderate depths; _Rhinonus_ is a
deep-sea fish.

II. _Ventral fins replaced by a pair of bifid filaments (barbels)
inserted below the glossohyal_: OPHIDIINÆ.

   OPHIDIUM.--Body elongate, compressed, covered with very small
   scales. Eye of moderate size. All the teeth small.

Small fishes from the Atlantic and Pacific. Seven species are known,
differing from one another in the structure of the air-bladder (see p.
145).

   GENYPTERUS is a larger form of _Ophidium_, in which the outer
   series of teeth in the jaws and the single palatine series
   contains strong teeth.

Three species from the Cape of Good Hope, South Australia, New Zealand,
and Chili are known. They grow to a length of five feet, and have an
excellent flesh, like cod, well adapted for curing. At the Cape they
are known by the name of “Klipvisch,” and in New Zealand as “Ling” or
“Cloudy Bay Cod.”

III. _No ventral fins whatever; vent at the throat_: FIERASFERINA.

These fishes (_Fierasfer_ and _Encheliophis_) are of very small
size and eel-like in shape; the ten species known are found in the
Mediterranean, Atlantic, and Indo-Pacific. As far as is known they
live parasitically in cavities of other marine animals, accompany
Medusæ, and more especially penetrate into the respiratory cavities of
Star-fishes and Holothurians. Not rarely they attempt other animals
less suited for their habits, as, for instance, Bivalves; and cases are
known in which they have been found imprisoned below the mantle of the
Mollusk, or covered over with a layer of the pearly substance secreted
by it. They are perfectly harmless to their host, and merely seek for
themselves a safe habitation, feeding on the animalcules which enter
with the water the cavity inhabited by them.

IV. _No ventral fins whatever; vent remote from the head; gill-openings
very wide, the gill-membranes not being united_: AMMODYTINA.

The “Sand-eels” or “Launces” (_Ammodytes_) are extremely common on
sandy shores of Europe and North America. They live in large shoals,
rising as with one accord to the surface, or diving to the bottom,
where they bury themselves with incredible rapidity in the sand.
They are much sought after for bait by fishermen, who discover their
presence on the surface by watching the action of Porpoises which
feed on them. These Cetaceans, when they meet with a shoal, know how
to keep it on the surface by diving below and swimming round it, thus
destroying large numbers of them. The most common species on the
British coast is the Lesser Sand-eel (_A. tobianus_); the Greater
Sand-eel (_A. lanceolatus_), which attains to a length of eighteen
inches; _A. siculus_, from the Mediterranean, scarcer in British seas.
Two species live on the American coasts, _A. americanus_ and _A.
dubius_; one in California, _A. personatus_. _Bleekeria_ from Madras is
the second genus of this group.

  [Illustration: Fig. 253.--Congrogadus subducens.]

V. _No ventral fins whatever; vent remote from the head; gill-openings
of moderate width, the gill-membranes being united below the throat,
not attached to the isthmus_: CONGROGADINA.

Only two fishes belong to this group--_Congrogadus_ from the Australian
coasts, and _Haliophis_ from the Red Sea.


                       FOURTH FAMILY--MACRURIDÆ.

_Body terminating in a long, compressed, tapering tail, covered with
spiny, keeled, or striated scales. One short ante__rior dorsal; the
second very long, continued to the end of the tail, and composed of
very feeble rays; anal of an extent similar to that of the second
dorsal; no caudal. Ventral fins thoracic or jugular, composed of
several rays._

  [Illustration: Fig. 254.--Scale of Macrurus trachyrhynchus.]

  [Illustration: Fig. 255.--Scale of Macrurus cœlorhynchus.]

  [Illustration: Fig. 256.--Scale from the lateral line of Macrurus
  australis.]

This family, known a few years ago from a limited number of examples,
representing a few species only, proves to be one which is distributed
over all oceans, occurring in considerable variety and great abundance
at depths of from 120 to 2600 fathoms. They are, in fact, Deep-sea
Gadoids, much resembling each other in the general shape of their body,
but differing in the form of the snout and in the structure of their
scales. About forty species are known, of which many attain a length of
three feet. They have been referred to the following genera:--

  [Illustration: Fig. 257.--Macrurus australis.]

   MACRURUS.--Scales of moderate size; snout produced, conical;
   mouth inferior.

   CORYPHÆNOIDES.--Scales of moderate size; snout obtuse, obliquely
   truncated; cleft of the mouth lateral.

   MACRURONUS.--Scales of moderate size, spiny; snout pointed;
   mouth anterior and lateral, with the lower jaw projecting.

   MALACOCEPHALUS.--Scales very small, ctenoid; snout short,
   obtuse, obliquely truncated.

   BATHYGADUS.--Scales small, cycloid; snout not projecting beyond
   the mouth; mouth wide, anterior, and lateral.

_Ateleopus_ from Japan and _Xenocephalus_ from New Ireland are genera
belonging to the Gadoid Anacanths, but are very imperfectly known.


             SECOND DIVISION--ANACANTHINI PLEURONECTOIDEI.

_Head and part of the body unsymmetrically formed._

This division consists of one family only:


                            PLEURONECTIDÆ.

The fishes of this family are called “Flat-fishes,” from their strongly
compressed, high, and flat body; in consequence of the absence of
an air-bladder, and of the structure of their paired fins, they are
unable to maintain their body in a vertical position, resting and
moving on one side of the body only. The side turned towards the
bottom is sometimes the left, sometimes the right, colourless, and
termed the “blind” side; that turned upwards and towards the light
is variously, and in some tropical species even vividly, coloured.
Both eyes are on the coloured side, on which side also the muscles
are more strongly developed. The dorsal and anal fins are exceedingly
long, without division. All the Flat-fishes undergo remarkable
changes with age, which, however, are very imperfectly known and not
yet fully understood, from the difficulty of referring larval forms
to their respective parents. The larvæ are, singularly enough, much
more frequently met in the open ocean than near the coast; they are
transparent, like _Leptocephali_; perfectly symmetrical, with an
eye on each side of the head, and swim in a vertical position like
other fishes. The manner in which one eye is transferred from the blind
to the coloured side is subject to discussion. Whilst some naturalists
believe that the eye turning round its axis pushes its way through the
yielding bones from the blind to the upper side, others hold that, as
soon as the body of the fish commences to rest on one side only, the
eye of that side, in its tendency to turn towards the light, carries
the surrounding parts of the head with it; in fact, the whole of the
fore-part of the head is twisted towards the coloured side, which is a
process of but little difficulty as long as the framework of the head
is still cartilaginous.

Flat-fishes when adult live always on the bottom, and swim with an
undulating motion of their body. Sometimes they rise to the surface;
they prefer sandy bottom, and do not descend to any considerable depth.
They occur in all seas, except in the highest latitudes and on rocky,
precipitous coasts, becoming most numerous towards the equator; those
of the largest size occur in the temperate zone. Some enter fresh water
freely, and others have become entirely acclimatised in ponds and
rivers. All are carnivorous.

Flat-fishes were not abundant in the tertiary epoch; the only
representative known is a species of _Rhombus_ from Monte Bolca.

The size and abundance of Flat-fishes, and the flavour of the flesh of
the majority of the species, render this family one of the most useful
to man; and especially on the coasts of the northern temperate zone,
their capture is one of the most important sources of profit to the
fishermen.

   PSETTODES.--Mouth very wide, the maxillary being more than
   one-half of that of the head. Each jaw armed with two series of
   long, slender, curved, distant teeth, the front teeth of the
   inner series of the lower jaw being the longest, and received
   in a groove before the vomer; vomerine and palatine teeth. The
   dorsal fin commences on the nape of the neck.

This genus fitly heads the list of Flat-fishes, having retained more
of symmetrical structure than the other members of the family, and,
therefore, their eyes are as often found on the right as on the left
side. It seems to swim, not unfrequently, in a vertical position. Only
one species is known, _Ps. erumei_, common in the Indian Ocean.

   HIPPOGLOSSUS.--Eyes on the right side; mouth wide, the length of
   the maxillary being one-third of that of the head. Teeth in the
   upper jaw in a double series; the anterior of the upper jaw and
   the lateral of the lower strong. The dorsal fin commences above
   the eye.

The “Holibut” (_H. vulgaris_) is the largest of all Flat-fishes,
attaining to a length of five and six feet, and a weight of several
hundredweights. It is found along the northern coasts of Europe, on the
coasts of Kamtschatka and California, particularly frequenting banks
situated at some distance from the coast, and at a depth of 50 to 120
fathoms.

Other genera, with nearly symmetrical mouth, in which the dorsal fin
commences above the eye, are _Hippoglossoides_ (the “Rough Dab”) and
_Tephritis_.

   RHOMBUS.--Eyes on the left side. Mouth wide, the length of the
   maxillary being more than one-third of that of the head. Each
   jaw with a band of villiform teeth, without canines; vomerine
   teeth, none on the palatines. The dorsal fin commences on the
   snout. Scales none or small.

Seven species from the North Atlantic and Mediterranean, of which the
most noteworthy are the “Turbot,” _Rh. maximus_, one of the most valued
food-fishes, and growing to a length of three feet; the “Turbot of the
Black Sea,” _Rh. mæoticus_, the body of which is covered with bony,
conical tubercles, which are as large as the eye; the “Brill,” _Rh.
lævis_, represented on the North American coasts by _Rh. aquosus_; the
“Whiff,” or “Mary-sole,” or “Sail-fluke,” _Rh. megastoma_; “Bloch’s
Top-knot,” _Rh. punctatus_ (described by Yarrell as _Rh. hirtus_, and
often confounded with the following species).

PHRYNORHOMBUS, differing from _Rhombus_ in lacking vomerine teeth. The
scales are very small and spiny.

The “Top-knot” (_Ph. unimaculatus_) occurs occasionally on the south
coast of England, and is more common in the Mediterranean; it is a
small species.

   ARNOGLOSSUS.--Mouth wide, the length of the maxillary being
   more or not much less than one-third of that of the head. Teeth
   minute, in a single series in both jaws; vomerine or palatine
   teeth none. The dorsal fin commences on the snout. Scales of
   moderate size, deciduous; lateral line with a strong curve above
   the pectoral. Eyes on the left side.

Seven species from European and Indian Seas. The “Scald-fish” (_A.
laterna_) is common in the Mediterranean, and extends to the south
coast of England; it is a small species.

   PSEUDORHOMBUS.--Mouth wide, the length of the maxillary being
   more than one-third of that of the head. Teeth in both jaws in a
   single series, of unequal size; vomerine or palatine teeth none.
   The dorsal fin commences on the snout. Scales small; lateral
   line with a strong curve anteriorly. Eyes on the left side.
   Interorbital space not concave.

A tropical genus with a few outlying species, represented chiefly in
the Indo-Pacific, and also in the Atlantic. Seventeen species.

   RHOMBOIDICHTHYS.--Mouth of moderate width or small. Teeth
   minute, in a single or double series; vomerine or palatine teeth
   none. Eyes separated by a concave more or less broad space. The
   dorsal fin commences on the snout. Scales ciliated; lateral line
   with a strong curve anteriorly. Eyes on the left side.

A tropical genus, but also represented in the Mediterranean and on the
coast of Japan. Sixteen species, the majority of which are prettily
coloured and ornamented with ocellated spots; in some species the adult
males have some of the fin-rays prolonged into filaments.

Other genera with nearly symmetrical mouth, in which the dorsal fin
commences before the eye, on the snout, are _Citharus_, _Anticitharus_,
_Brachypleura_, _Samaris_, _Psettichthys_, _Citharichthys_,
_Hemirhombus_, _Paralichthys_, _Liopsetta_, _Lophonectes_,
_Lepidopsetta_, and _Thysanopsetta_.

   PLEURONECTES.--Cleft of the mouth narrow, with the dentition
   much more developed on the blind side than on the coloured.
   Teeth in a single or in a double series, of moderate size;
   palatine and vomerine teeth none. The dorsal fin commences above
   the eye. Scales very small or entirely absent. Eyes generally on
   the right side.

This genus is characteristic of the littoral fauna of the northern
temperate zone, a few species ranging to the Arctic circle.
Twenty-three species are known, of which the following are the most
noteworthy: _P. platessa_, the “Plaice,” ranging from the coast of
France to Iceland; _P. glacialis_, from the Arctic coasts of North
America; _P. americanus_, the transatlantic representative of the
Plaice; _P. limanda_, the common “Dab;” _P. microcephalus_, the
“Smear-dab;” _P. cynoglossus_, the “Craig-fluke;” _P. flesus_, the
“Flounder.”

   RHOMBOSOLEA.--Eyes on the right side, the lower in advance of
   the upper. Mouth narrower on the right side than on the left;
   teeth on the blind side only, villiform; palatine and vomerine
   teeth none. The dorsal fin commences on the foremost part of
   the snout. Only one ventral which is continuous with the anal.
   Scales very small, cycloid; lateral line straight.

This genus represents _Pleuronectes_ in the Southern Hemisphere, but
consists of three species only, which occur on the coasts of New
Zealand, and are valued as food-fishes.

Other genera, with narrow unsymmetrical mouth, in which the upper eye
is not in advance of the lower, and which have pectoral fins, are
_Parophrys_, _Psammodiscus_, _Ammotretis_, _Peltorhamphus_, _Nematops_,
_Læops_, and _Poecilopsetta_.

   SOLEA.--Eyes on the right side, the upper being more or less
   in advance of the lower. Cleft of the mouth narrow, twisted
   round to the left side. Villiform teeth on the blind side only;
   vomerine or palatine teeth none. The dorsal fin commences on the
   snout, and is not confluent with the caudal. Scales very small,
   ctenoid; lateral line straight.

“Soles” are numerously represented in all suitable localities within
the temperate and tropical zones, with the exception of the southern
parts of the southern temperate zone, in which they are absent.
Some enter or live in fresh water. Nearly forty species are known.
British are _S. vulgaris_, the common “Sole;” _S. aurantiaca_, the
“Lemon-sole,” which is rather a southern species, and inhabits, on
the south coast of England, deeper water than the common Sole; _S.
variegata_, the “Banded Sole,” with very small pectoral fins; and _S.
minuta_, the “Dwarf-Sole.”--Allied to _Solea_ are _Pardachirus_ and
_Liachirus_ from the Indian coasts.

   SYNAPTURA.--Eyes on the right side, the upper in advance of
   the lower. Cleft of the mouth narrow, twisted round to the
   left side; minute teeth on the left side only. Vertical fins
   confluent. Scales small, ctenoid; lateral line straight.

Twenty species; with the exception of two from the Mediterranean
and coast of Portugal, all belong to the fauna of the Indian
Ocean.--Closely allied is _Aesopia_.

   GYMNACHIRUS.--Mouth very small, toothless. Scales none, lateral
   line straight. Eyes on the right side. The dorsal fin commences
   on the snout; caudal free. Pectorals rudimentary or entirely
   absent.

Two species from the Tropical Atlantic.

   CYNOGLOSSUS.--Eyes on the left side; pectorals none; vertical
   fins confluent. Scales ctenoid; lateral line on the left side
   double or triple; upper part of the snout produced backwards
   into a hook; mouth unsymmetrical, rather narrow. Teeth minute,
   on the right side only.

Abundant in the Indian seas, and especially on the flat sandy shores
of China. About thirty-five species are known, which rarely exceed a
length of eighteen inches. They are easily recognised by their long
narrow shape (which has been compared to a dog’s tongue) and the
peculiar form of their snout.

   To complete the list of Pleuronectoid genera, the following
   have to be mentioned: _Soleotalpa_ and _Apionichthys_, Soles
   with rudimentary eyes; _Ammopleurops_, _Aphoristia_, and
   _Plagusia_, which are closely allied to _Cynoglossus_, the
   latter genus having the lips provided with tentacles.


                       FOURTH ORDER--PHYSOSTOMI.

_All the fin-rays articulated, only the first of the dorsal and
pectoral fins is sometimes ossified. Ventral fins, if present,
abdominal, without spine. Air-bladder, if present, with a pneumatic
duct (except in Scombresocidæ)._


                        FIRST FAMILY--SILURIDÆ.

_Skin naked or with osseous scutes, but without scales. Barbels
always present; maxillary bone rudimentary, almost always forming a
support to a maxillary barbel. Margin of the upper jaw formed by the
intermaxillaries only. Suboperculum absent. Air-bladder generally
present, communicating with the organ of hearing by means of the
auditory ossicles. Adipose fin present or absent._

A large family, represented by numerous genera, which exhibit a great
variety of form and structure of the fins; they inhabit the fresh
waters of all the temperate and tropical regions; a few enter the sea
but keep near the coast. The first appearance of Siluroids is indicated
by some fossil remains in tertiary deposits of the highlands of Padang
in Sumatra, where _Pseudeutropius_ and _Bagarius_, types well
represented in the living Indian fauna, have been found. Also in North
America spines referable to Cat-fishes have been found in tertiary
formations.

The skeleton of the typical Siluroids shows many peculiarities. The
cranial cavity is not membranous on the sides, but closed as in the
Cyprinidæ, by the orbitosphenoids and the ethmoid that unite with
the prefrontals, carrying forward the cranial cavity to the nasal
bone, without leaving a membranous septum between the orbits. But the
supraoccipital is greatly developed, and in many the post-temporal is
united by suture to the sides of the cranium. In numerous members of
the family the skull is enlarged posteriorly, by dermal ossifications,
to form a kind of helmet which spreads over the nape; the lateral
angles of this production are formed by the suprascapulæ, augmented
and fixed by suture, and the median part is the extension of the
supraoccipital, which is generally very large, is connected anteriorly
with the frontal, and passing backwards between the postfrontals, the
parietals, the mastoids, and the suprascapulæ, goes past them all on
to the nape. The mastoids interpose between the postfrontals and the
parietals, so as to come in contact with the supraoccipital, and the
parietals but little developed are pressed to the back part of the
cranium, and in some instances wholly disappear.

The suprascapula most frequently unites to the mastoid by an immovable
suture, which includes the parietal when that bone is present, and
extends even to the supraoccipital. It gives out besides two processes,
one of them resting on the exoccipital and basi-occipital, or wedging
itself between them, and the other going to the first vertebra;
sometimes a plate from the exoccipital supports the same vertebra. This
vertebra, though it presents a pretty continuous centrum beneath, is in
reality composed of three or four coalescent vertebræ, as we ascertain
by its diapophyses, by the circular elevations of the neural canal, and
by the holes for the exit of the pairs of spinal nerves. There is great
variety in the development of the various processes of the bones we
have mentioned, and there is no less in the magnitude and connections
of the first three interneurals.

In general in the species which have a strong dorsal spine the second
and third interneurals unite to form a single plate, the “buckler;” the
great spine is articulated to the third interneural, and there is only
the vestige of a spine on the second interneural in form of a small
oval bone, forked below, whose function is to act as a bolt or fulcrum
to the great spine when the fish wishes to use it as an offensive
weapon. The great spine itself is joined by a ring to a second spine,
which belongs to the third interneural. This articulation by ring
exists in Lophius and a few other fishes not of this family.

The first interneural does not carry a ray, and it varies much in
the species whose helmet is continuous with the buckler, as in
many of the Bagri and Pimelodi. In these cases the supraoccipital,
extending backwards, conceals the first interneural, passing over it
to touch with its point the buckler formed by the second and third
interneurals. In other instances, as in Synodontis and Auchenipterus,
the supraoccipital and second interneural, forking and expanding,
inclose and join themselves to the first interneural, but leave a
larger or smaller space in the middle of the nuchal armour which they
contribute to form. When the point of the supraoccipital does not reach
quite to the second interneural, the first interneural remains free
from connection, and occasionally shows as a narrow plate interposed
between the other two; in such a case the helmet is not continuous with
the buckler.

The neural spines of the coalescent centra, which form the
apparently single first vertebra, concur also in sustaining the
nuchal plate-armour and the first great dorsal spine. They carry the
interneurals, are joined to them by suture, and one of them is often
inclined towards the occiput to assist in sustaining the head; in fact,
this part of the skeleton is constructed to give firm mutual support.

The shoulder-girdle of the Siluroids is also formed to give
resistance to the strong weapon with which it is frequently armed. The
post-temporal, as we have said above, is often united by suture to the
cranium, and it obtains support below by one or two processes that
are fixed on the basioccipitals and on the diapophysis of the first
vertebra.

In most osseous fishes the clavicle completes the lower key of the
scapular arch in joining its fellow by suture or synchondrosis without
the intervention of the coracoid; but in the Siluroids the coracoid
descends to take part in this joint, and sometimes even to occupy the
half of the suture, which is not unfrequently constructed of very deep
interlocking serratures. The solidity of this base of the pectoral
spine is further augmented by the intimate union of the coracoid
and scapula, which often extends to junction by suture, or even to
coalescence; and these bones, moreover, give off two bony arches--the
first a slender one, arising from the salient edge of the coracoid
near the pectoral fin, and going to the interior face of the scapular
that is applied to the interior surface of the ascending branch of the
clavicle; the second and broader supplementary arch is often perforated
by a large hole; it also emanates from the same salient edge of the
radius, but proceeds in opposite direction to the inferior edge of the
clavicle, a little before the insertion of the pectoral spine. The two
arches give attachments to the muscles that move this spine; in the
Synodontes and many Bagri the upper arch remains in a cartilaginous or
ligamentous condition, while in Malapterurus it is the lower arch that
does not ossify, but both are fully formed in the Siluri and many other
Siluroids more closely allied to that typical genus. The postclavicle
is also wanting in the Siluroids. The pterygoid and entopterygoid are
reduced to a single bone, the symplectic is wholly wanting, and the
palatine is merely a slender cylindrical bone. The sub-operculum is
likewise constantly absent in all the Siluroids.

The great number of different generic types has necessitated a further
division of this family into eight subdivisions:

I. SILURIDÆ HOMALOPTERÆ.--_The dorsal and anal fins are very long,
nearly equal in extent to the corresponding parts of the vertebral
column._


                            _a_. CLARIINA.

   CLARIAS.--Dorsal fin extending from the neck to the caudal,
   without adipose division. Cleft of the mouth transverse,
   anterior, of moderate width; barbels eight; one pair of nasal,
   one of maxillary, and two pairs of mandibulary barbels. Eyes
   small. Head depressed; its upper and lateral parts are osseous,
   or covered with only a very thin skin. A dendritic accessory
   branchial organ is attached to the convex side of the second and
   fourth branchial arches, and received in a cavity behind the
   gill-cavity proper. Ventrals six-rayed; only the pectoral has a
   pungent spine. Body eel-like.

Twenty species from Africa, the East Indies, and the intermediate parts
of Asia; some attain to a length of six feet. They inhabit muddy and
marshy waters; the physiological function of the accessory branchial
organ is not known. Its skeleton is formed by a soft cartilaginous
substance covered by mucous membrane, in which the vessels are
imbedded. The vessels arise from branchial arteries, and return the
blood into branchial veins. The vernacular name of the Nilotic species
is “Carmoot.”

   HETEROBRANCHUS differs from _Clarias_ only in the structure of
   the dorsal fin, the posterior portion of which is adipose.

The geographical range of this genus is not quite co-extensive with
that of _Clarias_, inasmuch as it is limited to Africa and the
East-Indian Archipelago. Six species.


                            _b_. PLOTOSINA.

   PLOTOSUS.--A short dorsal fin in front, with a pungent spine; a
   second long dorsal coalesces with the caudal and anal. Vomerine
   teeth molar-like. Barbels eight or ten; one immediately before
   the posterior nostril, which is remote from the anterior, the
   latter being quite in front of the snout. Cleft of the mouth
   transverse. Eyes small. The gill-membranes are not confluent
   with the skin of the isthmus. Ventral fins many-rayed. Head
   depressed; body elongate.

  [Illustration: Fig. 258.--Mouth of Cnidoglanis megastoma,
  Australia.]

Three species are known from brackish waters of the Indian Ocean freely
entering the sea. _Plotosus anguillaris_ is distinguished by two white
longitudinal bands, and is one of the most generally distributed
and common Indian fishes.--_Copidoglanis_ and _Cnidoglanis_ are two
very closely allied forms, chiefly from rivers and brackish waters
of Australia. None of these Siluroids attain to a considerable size.
_Chaca_, from the East Indies, belongs likewise to this sub-family.

  [Illustration: Fig. 259.--Cnidoglanis microcephalus.]

II. SILURIDÆ HETEROPTERÆ.--_The rayed dorsal fin is very little
developed, and, if it is present, it belongs to the abdominal portion
of the vertebral column; the adipose fin is exceedingly small or
absent. The extent of the anal is not much inferior to that of the
caudal vertebral column. The gill-membranes overlap the isthmus,
remaining more or less separate_: SILURINA.

   SACCOBRANCHUS.--Adipose fin none; dorsal very short, without
   pungent spine, placed above the ventrals. Cleft of the mouth
   transverse, anterior, of moderate width; barbels eight. Eyes
   rather small. The upper and lateral parts of the head osseous
   or covered with a very thin skin. Gill-cavity with an accessory
   posterior sac, extending backwards between the muscles along
   each side of the abdominal and caudal portions of the vertebral
   column. Ventrals six-rayed.

Small fishes from East Indian rivers; four species are known. The
lung-like extension of the branchial cavity receives water, and is
surrounded by contractile transverse muscular fibres by which the water
is expelled at intervals. The vessels of the sac take their origin in
the last branchial artery, and pass into the aorta.

   SILURUS.--No adipose fin; one very short dorsal, without pungent
   spine. Barbels four or six, one to each maxillary, and one or
   two to each mandible. Nostrils remote from each other. Head
   and body covered with soft skin. The eye is situated above the
   level of the angle of the mouth. The dorsal fin is anterior to
   the ventrals which are composed of more than eight rays. Caudal
   rounded.

This genus, of which five species are known, inhabits the temperate
parts of Europe and Asia. The species which has given the name to
the whole family, is the “Wels” of the Germans, _Silurus glanis_. It
is found in the fresh waters east of the Rhine, and is, besides the
Sturgeons, the largest of European Freshwater-fishes, and the only
species of this family which occurs in Europe. Barbels six. It attains
to a weight of 300 or 400 lbs., and the flesh, especially of smaller
specimens, is firm, flaky, and well flavoured. Aristotle described
it under the name of _Glanis_. Its former occurrence in Scotland has
justly been denied. In China it is represented by a similar species,
_S. asotus_, which, however, has four barbels only.

  [Illustration: Fig. 260.--The “Wels,” Siluris glanis.]

This sub-family is well represented by various other genera in the
fresh waters of the African as well as Indian region. African genera
are _Schilbe_ and _Eutropius_; East Indian: _Silurichthys_, _Wallago_,
_Belodontichthys_, _Eutropiichthys_, _Cryptopterus_, _Callichrous_,
_Hemisilurus_, _Siluranodon_, _Ailia_, _Schilbichthys_, _Lais_,
_Pseudeutropius_, _Pangasius_, _Helicophagus_, and _Silondia_.

III. SILURIDÆ ANOMALOPTERÆ.--_Dorsal and adipose fins very short,
the former belonging to the caudal vertebral column; anal very long.
Ventrals in front of the dorsal. Gill-membranes entirely separate,
overlapping the isthmus_: (HYPOPHTHALMINA.)

   HYPOPHTHALMUS.--Dorsal fin with seven rays, the first of which
   is slightly spinous. The lower jaw is rather the longer. Barbels
   six, those of the mandible long. No teeth; intermaxillaries very
   feeble. Head covered with skin. Eye of moderate size, situated
   behind and below the angle of the mouth. Ventrals small,
   six-rayed.

Four species from tropical America. The second genus of this sub-family
is _Helogenes_ from the Essequibo.


IV. SILURIDÆ PROTEROPTERÆ.--_The rayed dorsal fin is always present,
short, with not more than twelve short rays, and belongs to the
abdominal portion of the vertebral column, being placed in advance of
the ventrals. The adipose fin is always present and well developed,
although frequently short. The extent of the anal is much inferior
to that of the caudal vertebral column. The gill-membranes are not
confluent with the skin of the isthmus, their posterior margin always
remaining free even if they are united with each other. Whenever the
nasal barbel is present it belongs to the posterior nostril._


                             _a._ BAGRINA.

   BAGRUS.--Adipose fin long; a short dorsal with a pungent spine
   and nine or ten soft rays; anal fin short, with less than twenty
   rays. Barbels eight. The anterior and posterior nostrils are
   remote from each other, the posterior being provided with a
   barbel. Teeth on the palate in a continuous band. Eyes with a
   free orbital margin. Caudal forked; ventrals six-rayed.

This genus consists of two species only, common in the Nile, viz.
the “Bayad,” _B. bayad_, and _B. docmac_. Both grow to a large size,
exceeding a length of five feet, and are eaten. _Chrysichthys_ and
_Clarotes_ are two other Siluroid genera from African rivers, closely
allied to Bagrus. Similar Siluroids are common in the East Indies, and
have been referred to the following genera: _Macrones_, _Pseudobagrus_,
_Liocassis_, _Bagroides_, _Bagrichthys_, _Rita_, _Acrochordonichthys_,
_Akysis_.


                            _b._ AMIURINA.

   AMIURUS.--Adipose fin of moderate length; a short dorsal with a
   pungent spine and six soft rays; anal fin of moderate length.
   Barbels eight. The anterior and posterior nostrils are remote
   from each other, the posterior being provided with a barbel.
   Palate edentulous. Head covered with skin above. Ventrals
   eight-rayed.

The “Cat-fishes” of North America, of which about a dozen different
species are known. One species occurs in China. Allied, but smaller
forms are _Hopladelus_ and _Noturus_, likewise from North
America.


                           _c_. PIMELODINA.

   PLATYSTOMA.--Adipose fin of moderate length; a short dorsal fin
   with a pungent spine and six or seven soft rays; anal fin rather
   short. Snout very long, spatulate, with the upper jaw more or
   less projecting; the upper surface of the head not covered by
   the skin. Barbels six; the anterior and posterior nostrils
   remote from each other, none with a barbel. Palate toothed.
   Caudal forked; ventrals six-rayed, inserted behind the dorsal.

Twelve species from South America, some attaining a length of six feet,
the majority being ornamented with deep-black spots or bands. Allied
genera from South America, likewise distinguished by a long spatulate
snout, are _Sorubim_, _Hemisorubim_, and _Platystomatichthys_, whilst
_Phractocephalus_, _Piramutana_, _Platynematichthys_, _Piratinga_,
_Bagropsis_, and _Sciades_, have a snout of ordinary length. The
barbels of some are of extraordinary length, and not rarely dilated and
band-like.

   PIMELODUS.--Adipose fin well developed; dorsal fin short, with a
   more or less pungent spine and six rays; anal fin short. Barbels
   six, cylindrical or slightly compressed, none of them belonging
   to either of the nostrils, which are remote from each other.
   Palate edentulous. Ventrals six-rayed, inserted behind the
   dorsal.

Of all South American genera this is represented by the greatest
number of species, more than forty being well characterised; they
differ chiefly with regard to the length of the adipose fin and
barbels, and the strength of the dorsal spine. Singularly, two species
(_P. platychir_ and _P. balayi_), are found in West Africa. The
majority are of but moderate size and plain coloration.--Allied South
American genera (also without teeth on the palate), are _Pirinampus_,
_Conorhynchus_, _Notoglanis_, _Callophysus_, _Lophiosilurus_.

   AUCHENOGLANIS.--Adipose fin rather long, dorsal short, with
   a pungent spine and seven rays; anal short. Snout produced,
   pointed, with narrow mouth. Barbels six, none of which belongs
   to either of the nostrils, which are remote from each other. The
   teeth of each jaw form a pair of small elliptic patches which
   are longer than broad; palate edentulous. Eyes of moderate size.
   Ventrals six-rayed.

One species, _Au. biscutatus_, from the Nile, Senegal, and other
West African rivers.


                             _d._ ARIINA.

   ARIUS.--Adipose fin of moderate length or short; a short dorsal
   fin with a pungent spine and seven soft rays; anal fin rather
   short. Head osseous above; barbels six, four at the mandible,
   none at either of the nostrils which are close together.
   Eyes with a free orbital margin. Caudal fin forked; ventrals
   six-rayed, behind the dorsal.

Of all Siluroid genera this has the greatest number of species (about
seventy), and the widest distribution, being represented in almost
all tropical countries which are drained by large rivers; some of
the species prefer brackish to fresh water, and a few enter the
sea, but keep near to the coast. Some of the species are of small
size, whilst others exceed a length of five feet. The extent of the
armature of the neck and the dentition vary much in the different
species, and affords two of the principal characters by which the
species are separated.--The following genera are allied to _Arius_,
_Galeichthys_ from South Africa; _Genidens_ and _Paradiplomystax_ from
Brazil; _Diplomystax_ from Chile; _Aelurichthys_ from Central and
South America; _Hemipimelodus_, _Ketengus_, _Osteo__geniosus_, and
_Batrachocephalus_ from the East Indies; and _Atopochilus_ from West
Africa.

  [Illustration: Fig. 261.--Arius australis, from Queensland.]


                            _e._ BAGARIINA.

   BAGARIUS.--Adipose fin rather short; a short dorsal with one
   spine and six rays; anal fin of moderate length. Barbels eight,
   of which one pair stands between the anterior and posterior
   nostrils which are close together. Head naked above. Caudal fin
   deeply forked; ventrals rays six. Thorax without longitudinal
   plaits of the skin.

A large Siluroid (_B. bagarius_) from rivers of India and Java;
exceeding a length of six feet.

  [Illustration: Fig. 262.--Euglyptosternum coum, thoracic adhesive
  apparatus.]

   EUGLYPTOSTERNUM.--Adipose fin of moderate length; a short
   dorsal with a pungent spine and six rays; anal fin short.
   Barbels eight, of which one pair is placed between the anterior
   and posterior nostrils which are close together. Teeth on the
   palate villiform, in two separate patches. Eyes small, below the
   skin. Caudal forked; ventral rays six. Pectorals horizontal,
   with a thoracic adhesive apparatus between, which is formed by
   longitudinal plaits of the skin.

This fish (_Eu. coum_) inhabits the river Coic in Syria, and is about
twelve inches long. The plaited structure on the thorax probably
increases the capability of the fish of maintaining its position
in the rapid current of the stream, a function which appears to be
chiefly performed by the horizontally expanded pectoral fins. A similar
structure is found in _Glyptosternum_, a genus represented by eight
species in mountain streams of the East Indies, and differing from the
Syrian species in lacking the teeth on the palate.

V. SILURIDÆ STENOBRANCHIÆ.--_The rayed dorsal fin is short, if
present, belonging to the abdominal portion of the vertebral column,
the ventrals being inserted behind it (except in Rhinoglanis). The
gill-membranes are confluent with the skin of the isthmus._


                            _a_. DORADINA.

Some of the genera have no bony shields along the lateral line,
and a small adipose fin or none whatever; all of these are
South American--_Ageniosus_, _Tetranematichthys_, _Euanemus_,
_Auchenipterus_, _Glanidium_, _Centromochlus_, _Trachelyopterus_,
_Cetopsis_, and _Astrophysus_.

Others have a series of bony scutes along the middle of the side; they
form the genus _Doras_ with two closely allied forms, _Oxydoras_ and
_Rhinodoras_. Some twenty-five species are known, all from rivers of
tropical America, flowing into the Atlantic. These fishes have excited
attention by their habit of travelling, during the dry season, from a
piece of water about to dry up, in quest of a pond of greater capacity.
These journeys are occasionally of such a length that the fish spends
whole nights on the way, and the bands of scaly travellers are
sometimes so large that the Indians who happen to meet them, fill many
baskets of the prey thus placed in their hands. The Indians supposed
that the fish carry a supply of water with them, but they have no
special organs, and can only do so by closing the gill-openings, or by
retaining a little water between the plates of their bodies, as Hancock
supposes. The same naturalist adds that they make regular nests, in
which they cover up their eggs with care and defend them, male and
female uniting in this parental duty until the eggs are hatched. The
nest is constructed at the beginning of the rainy season, of leaves,
and is sometimes placed in a hole scooped out in the beach.

Finally, in the last genus, the lateral scutes are likewise absent,
viz. in

   SYNODONTIS.--The adipose fin is of moderate length or rather
   long; the dorsal fin has a very strong spine and seven soft
   rays. The teeth in the lower jaw are movable, long, very thin
   at the base, and with a slightly-dilated brown apex. Mouth
   small. Barbels six, more or less fringed with a membrane or with
   filaments. Neck with broad dermal bones.

Synodontis is characteristic of the fauna of tropical Africa, where it
is represented by fifteen species. Several occur in the Nile, and are
known by the vernacular name “Schal.” Some attain a length of two feet.
The species figured is from West Africa, and characterised by its long
upper jaw.

  [Illustration: Fig. 263.--Synodontis xiphias.]


                          _b_. RHINOGLANINA.

   RHINOGLANIS.--Two dorsal fins, both composed of rays, the first
   with a strong spine; anal rather short. Barbels six; anterior
   and posterior nostrils close together, the posterior very large,
   open. Neck with broad dermal bones. Ventrals with seven rays,
   inserted below the posterior rays of the first dorsal fin.

   This Siluroid is known from a single example only one and a
   half inches long, obtained at Gondokoro on the Upper Nile.
   _Callomystax_ represents this type in the Ganges and Indus.


                          _c_. MALAPTERURINA.

   MALAPTERURUS.--One dorsal fin only, which is adipose and
   situated before the caudal; anal of moderate length or short;
   caudal rounded; ventrals six-rayed, inserted somewhat behind the
   middle of the body; pectorals without pungent spine. Barbels
   six: one to each maxillary and two on each side of the mandible.
   The anterior and posterior nostrils are remote from each other.
   No teeth on the palate. The entire head and body covered with
   soft skin. Eyes small. Gill-opening very narrow, reduced to a
   slit before the pectoral.

The “Electric Cat- or Sheath-fishes” are not uncommon in the fresh
waters of tropical Africa; three species have been described, of which
_M. electricus_ occurs in the Nile; they grow to a length of about
four feet. Although the first dorsal fin is absent, its position (if it
had been developed) is indicated by a rudimentary interneural spine,
which rests in the cleft of the neural process of the first vertebra.
The electric organ extends over the whole body, but is thickest on the
abdomen; it lies between two aponeurotic membranes, below the skin, and
consists of rhomboidal cells which contain a rather firm gelatinous
substance. The electric nerve takes its origin from the spinal chord,
does not enter into connection with ganglia, and consists of a single
enormously-strong primitive fibre, which distributes its branches in
the electric organ.

  [Illustration: Fig. 264.--Malapterurus electricus.]

VI. SILURIDÆ PROTEROPODES.--_The rayed dorsal fin is always present and
rather short; the ventrals are inserted below (very rarely in front
of) the dorsal. The gill-membranes are confluent with the skin of the
isthmus, the gill-opening being reduced to a short slit. Pectorals and
ventrals horizontal. Vent before, or not much behind, the middle of the
length of the body._


                          _a_. HYPOSTOMATINA.

   STYGOGENES.--Adipose fin short; dorsal and anal short; the outer
   fin-rays somewhat thickened and rough; palate toothless; cleft
   of the mouth of moderate width, with a maxillary barbel on each
   side; a short broad flap on each side between the nostrils,
   which are close together. Lower lip very broad, pendent. Eyes
   small, covered with transparent skin. Head covered with soft
   skin. Ventrals six-rayed.

These small Siluroids, which are called “Preñadillas” by the natives,
together with the allied _Arges_, _Brontes_, and _Astroplebus_, have
received some notoriety through Humboldt’s accounts, who adopted
the popular belief that they live in subterranean waters within the
bowels of the active volcanoes of the Andes, and are ejected with
streams of mud and water during eruptions. Humboldt himself considers
it very singular that they are not cooked and destroyed whilst they
are vomited forth from craters or other openings. The explanation of
their appearance during volcanic eruptions is, that they abound in the
numerous lakes and torrents of the Andes, that they are killed by the
sulphuretted gases escaping during an eruption, and swept down by the
torrents of water issuing from the volcano.

   CALLICHTHYS.--Adipose fin short, supported anteriorly by a short
   movable spine; dorsal with a feeble spine and seven or eight
   rays; anal short. Teeth minute or entirely absent; cleft of the
   mouth rather narrow, with a pair of maxillary barbels on each
   side, which are united at the base. Eyes small. Head covered
   with osseous plates; body wholly protected by two series of
   large imbricate shields on each side. Ventrals six-rayed.

Twelve species of this genus are known; they are small, and similarly
distributed as _Doras_, with which they have much in common as regards
their mode of life. They likewise are able to travel over land, and
construct nests for their ova.

  [Illustration: Fig. 265.--Callichthys armatus, from the Upper
  Amazon. Natural size.]

   CHÆTOSTOMUS.--A short adipose fin, supported anteriorly by a
   short, compressed, curved spine; dorsal fin of moderate length,
   with from eight to ten rays, the first of which is simple; anal
   fin short; ventral six-rayed; pectoral with a strong spine. Head
   and body completely cuirassed, the lower parts being sometimes
   naked; body rather short, with four or five longitudinal series
   of large imbricate scutes on each side; tail not depressed.
   Snout produced, obtuse in front; mouth inferior, transverse,
   with a single series of generally very fine bent teeth in both
   jaws. Interoperculum very movable and armed with erectile spines.

   This genus, with the allied _Plecostomus_, _Liposarcus_,
   _Pterygoplichthys_, _Rhinelepis_, _Acanthicus_, and
   _Xenomystus_, is well represented in the fresh waters of South
   America, whence about sixty species are known. The majority
   do not exceed a length of twelve inches, but some attain to
   more than double that size. In some of the species the male is
   provided with long bristles round the margin of the snout and
   interoperculum.

  [Illustration: Fig. 266.--Upper and Lower side of the head of
  _Chætostomus heteracanthus_, Upper Amazons.]

   _Hypoptopoma._--Differing from _Chætostomus_ in the peculiar
   formation of the head, which is depressed, spatulate, the eyes
   being on the lateral edge of the head. The movable gill-covers
   are reduced to two bones, neither of which is armed, viz.--the
   operculum small and placed as in _Chætostomus_, and a second,
   larger one, separated from the eye by the narrow sub-orbital
   ring, and placed at the lower side of the head.

  [Illustration: Fig. 267.--_Hypoptopoma thoracatum_, Upper
  Amazons. Natural size.]

   LORICARIA.--One short dorsal fin; anal short; the outer ray
   of each fin thickened, but flexible. Head depressed, with the
   snout more or less produced and spatulate. Mouth situated at the
   lower side of the snout, remote from its extremity, transverse,
   surrounded by broad labial folds which are sometimes fringed;
   a short barbel at each corner of the mouth. Teeth in the jaws
   small, bent, with a dilated, notched apex, in a single series,
   sometimes absent. Head and body cuirassed; tail depressed, long;
   eye rather small or of moderate size.

  [Illustration: Fig. 268.--_Loricaria lanceolate_, Upper
  Amazons. Natural size.]

Small fishes from rivers of tropical America; about twenty-six species
are known. The male of some species has a bearded or bristly snout.

   ACESTRA differs from _Loricaria_ in having the snout much
   prolonged.

   SISOR.--Head depressed, spatulate; trunk depressed; tail
   long and thin. One short dorsal fin; anal short; ventrals
   seven-rayed. Head partially osseous, rough; a series of bony
   plates along the median line of the back; lateral line rough.
   Eyes very small. Mouth inferior, small, transverse, with
   barbels; teeth none.

A single species, _S. rhabdophorus_, from rivers of northern Bengal.
Allied to this genus is _Erethistes_ from Assam.

   PSEUDECHENEIS.--Adipose fin of moderate length; a short dorsal
   with one spine and six rays; anal fin rather short. Barbels
   eight. Mouth small, inferior. Head depressed, covered with soft
   skin above; eyes small, superior. Caudal fin forked; pectorals
   horizontal, with a thoracic adhesive apparatus between, formed
   by transverse plaits of the skin. Ventrals six-rayed.

A very small species, inhabiting the mountain-streams of Khassya; by
means of the adhesive apparatus it is enabled to hold on to stones,
thus preventing the current from sweeping it away. _Exostoma_ is
a similar small Siluroid from Indian mountain-streams, but without the
thoracic apparatus; probably its mouth performs the same function.


                           _b_. ASPREDININA.

   ASPREDO.--Adipose fin none; dorsal short, without pungent spine;
   anal very long, but not united with the caudal. Head broad,
   much depressed; tail very long and slender. Barbels not less
   than six, one of which is attached to each intermaxillary; none
   at the nostrils. Eyes very small. Head covered with soft skin;
   the anterior and posterior nostrils are remote from each other.
   Ventrals six-rayed.

Six species are known from Guyana; the largest grows to a length
of about eighteen inches. The remarkable mode of taking care of
their ova has been noticed above (p. 161, Fig. 72). _Bunocephalus_,
_Bunocephalichthys_, and _Harttia_, from tropical America, are other
genera of this sub-family which remain to be mentioned.

VII. SILURIDÆ OPISTHOPTERÆ.--_The rayed dorsal fin is always present,
short, and placed above or behind the middle of the length of the body,
above or behind the ventrals which, however, are sometimes absent;
anal short. Nostrils remote from each other; if a nasal barbel is
present, it belongs to the anterior nostril. Lower lip not reverted.
The gill-membranes are not confluent with the skin of the isthmus_:
NEMATOGENYINA and TRICHOMYCTERINA.

The genera _Heptapterus_, _Nematogenys_, _Trichomycterus_,
_Eremophilus_, and _Pariodon_, belong to this sub-family. They are
small South American Siluroids, the majority of which inhabit waters at
high altitudes, up to 14,000 feet above the level of the sea. In the
Andes they replace the Loaches of the Northern Hemisphere, which they
resemble in appearance and habits, and even in coloration, offering a
striking example of the fact that similar forms of animals are produced
under similar external physical conditions.

VIII. SILURIDÆ BRANCHICOLÆ.--_The rayed dorsal fin is present, short,
and placed behind the ventrals; anal short. Vent far behind the middle
of the length of the body. Gill-membranes confluent with the skin of
the isthmus._

_Stegophilus_ and _Vandellia_, two genera from South America,
comprising the smallest and least developed Siluroids. Their body is
narrow, cylindrical, and elongate; a small barbel at each maxillary;
the operculum and interoperculum are armed with short stiff spines. The
natives of Brazil accuse these fishes of entering and ascending the
urethra of persons while bathing, causing inflammation and sometimes
death. This requires confirmation, but there is no doubt that they live
parasitically in the gill-cavity of larger fishes (_Platystoma_), but
probably they enter these cavities only for places of safety, without
drawing any nourishment from their host.


                       SECOND FAMILY--SCOPELIDÆ.

_Body naked or scaly. Margin of the upper jaw formed by the
intermaxillary only; opercular apparatus sometimes incompletely
developed. Barbels none. Gill-opening very wide; pseudobranchiæ well
developed. Air-bladder none. Adipose fin present. The eggs are enclosed
in the sacs of the ovary, and excluded by oviducts. Pyloric appendages
few in number or absent. Intestinal tract very short._

Exclusively marine, the majority being either pelagic or deep-sea
forms. Of fossil remains the following have been referred to this
family:--_Osmeroides_, from Mount Lebanon, which others believe to be
a marine salmonoid; _Hemisaurida_, from Comen, allied to _Saurus_;
_Parascopelus_ and _Anapterus_, from the miocene of Licata, the latter
genus allied to _Paralepis_.

   SAURUS (inclus. _Saurida_).--Body sub-cylindrical, rather
   elongate, covered with scales of moderate size; head oblong;
   cleft of the mouth very wide; intermaxillary very long,
   styliform, tapering; maxillary thin, long, closely adherent
   to the intermaxillary. Teeth card-like, some being elongate,
   slender; all can be laid downwards and inwards. Teeth on the
   tongue, and palatine bones. Eye of moderate size. Pectorals
   short; ventrals eight- or nine-rayed, inserted in advance of the
   dorsal, not far behind the pectorals. Dorsal fin nearly in the
   middle of the length of the body, with thirteen or less rays;
   adipose fin small; anal short or of moderate length; caudal
   forked.

Fifteen species of small size, from the shores of the tropical and
sub-tropical zones. The species figured on p. 42, Fig. 5, occurs on the
north-west coast of Australia and in Japan.

   BATHYSAURUS.--Shape of the body similar to that of _Saurus_,
   sub-cylindrical, elongate, covered with small scales. Head
   depressed, with the snout produced, flat above. Cleft of the
   mouth very wide, with the lower jaw projecting; intermaxillary
   very long, styliform, tapering, not movable. Teeth in the jaws,
   in broad bands, not covered by lips, curved, unequal in size
   and barbed at the end. A series of similar teeth runs along the
   whole length of each side of the palate. Eye of moderate size,
   lateral. Pectoral of moderate length. Ventral eight-rayed,
   inserted immediately behind the pectoral. Dorsal fin in the
   middle of the length of the body, with about eighteen rays.
   Adipose fin absent or present. Anal of moderate length. Caudal
   emarginate.

Deep-sea fishes, obtained in the Pacific at depths varying from 1100 to
2400 fathoms. The largest example is twenty inches long. Two species.

   BATHYPTEROIS.--Shape of the body like that of an _Aulopus_. Head
   of moderate size, depressed in front, with the snout projecting,
   the large mandible very prominent beyond the upper jaw. Cleft
   of the mouth wide; maxillary developed, very movable, much
   dilated behind. Teeth in narrow villiform bands in the jaws. On
   each side of the broad vomer a small patch of similar teeth;
   none on the palatines or on the tongue. Eye very small. Scales
   cycloid, adherent, of moderate size. Rays of the pectoral fin
   much elongated, some of the upper being separate from the rest,
   and forming a distinct division. Ventrals abdominal, with the
   outer rays prolonged, eight-rayed. Dorsal fin inserted in the
   middle of the body, above or immediately behind the root of the
   ventral, of moderate length. Adipose fin present or absent. Anal
   short. Caudal forked.

This very singular form is one of the discoveries of the “Challenger;”
it is widely distributed over the seas of the Southern Hemisphere, in
depths varying from 520 to 2600 fathoms. The elongate pectoral rays
are most probably organs of touch. Four species were discovered, the
largest specimen being thirteen inches long.

   HARPODON.--Body elongate, covered with very thin, diaphanous,
   deciduous scales. Head thick, with very short snout; its bones
   are very soft, and the superficial ones are modified into wide
   muciferous cavities; the lateral canal of the body is also
   very wide, and a pair of pores corresponds to each scale of the
   lateral line, one being above, the other below the scale. Cleft
   of the mouth very wide; intermaxillary very long, styliform,
   tapering; maxillary absent. Teeth card-like, recurved, unequal
   in size; the largest are in the lower jaw, and provided with a
   single barb at the posterior margin of the point. Eye small.
   Ventral fins long, nine-rayed, inserted below the anterior
   dorsal rays; dorsal fin in the middle of the length of the
   body; adipose fin small; anal of moderate length; caudal fin
   three-lobed, the lateral line being continued along the central
   lobe. Centre of the vertebræ open in the middle.

Two species only are known of this singular genus; both are evidently
inhabitants of considerable depths, and periodically come nearer to
the surface. One (_H. nehereus_) is well known in the East Indies,
being of excellent flavour. When newly taken its body is brilliantly
phosphorescent. When salted and dry it is known under the names of
“Bombay-ducks” or “Bummaloh,” and exported in large quantities from
Bombay and the coast of Malabar. The second species (_H. microchir_)
exceeds the other in length, and has been found in the sea off Japan.

  [Illustration: Fig. 269.--Scopelus boops.]

   SCOPELUS.--Body oblong, more or less compressed, covered with
   large scales. Series of phosphorescent spots run along the lower
   side of the body, and a similar glandular substance sometimes
   occupies the front of the snout and the back of the tail. Cleft
   of the mouth very wide. Intermaxillary very long, styliform,
   tapering; maxillary well developed. Teeth villiform. Eye large.
   Ventrals eight-rayed, inserted immediately in front of or below
   the anterior dorsal rays. Dorsal fin nearly in the middle of
   the length of the body; adipose fin small; anal generally long;
   caudal forked. Branchiostegals from eight to ten.

The fishes of this genus are small, of truly pelagic habits, and
distributed over all the temperate and tropical seas; they are so
numerous that the surface-net, when used during a night of moderate
weather, scarcely ever fails to enclose some specimens. They come to
the surface at night only; during the day and in very rough weather
they descend to depths where they are safe from sunlight or the
agitation of the water. Some species never rise to the surface; indeed,
Scopeli have been brought up in the dredge from almost any depth to
2500 fathoms. Thirty species are known. _Gymnoscopelus_ differs from
_Scopelus_ in lacking scales.

   IPNOPS.--Body elongate, sub-cylindrical, covered with large,
   thin, deciduous scales, and without phosphorescent organs. Head
   depressed, with broad, long, spatulate snout, the whole upper
   surface of which is occupied by a most peculiar organ of vision
   (or luminosity), longitudinally divided in two symmetrical
   halves. Bones of the head well ossified. Mouth wide, with the
   lower jaw projecting; maxillary dilated behind. Both jaws with
   narrow bands of villiform teeth; palate toothless. Pectoral and
   ventral fins well developed, and, owing to the shortness of the
   trunk, close together. Dorsal fin at a short distance behind
   the vent; adipose fin none; anal fin moderately long; caudal
   subtruncated. Pseudobranchiæ none.

This singular genus, one of the “Challenger” discoveries, is known
from four examples, obtained at depths varying between 1600 and 2150
fathoms, off the coast of Brazil, near Tristan d’Acunha and north of
Celebes. All belong to one species, _I. murrayi_. The eye seems to
have lost its function of vision and assumed that of producing light.
The specimens are from 4 to 5½ inches long.

   PARALEPIS.--Head and body elongate, compressed, covered with
   deciduous scales. Cleft of the mouth very wide; maxillary
   developed, closely adherent to the intermaxillary. Teeth in
   a single series, unequal in size. Eye large. Ventrals small,
   inserted opposite or nearly opposite the dorsal. Dorsal fin
   short, on the hinder part of the body; adipose fin small; anal
   elongate, occupying the end of the tail; caudal emarginate.

Three species; small pelagic fishes from the Mediterranean and
Atlantic.--_Sudis_, from the Mediterranean, has a dentition
slightly different from that of _Paralepis_.

   Plagyodus.--Body elongate, compressed, scaleless; snout much
   produced, with very wide cleft of the mouth. Intermaxillary very
   long and slender; maxillary thin, immovable. Teeth in the jaws
   and of the palate very unequal in size, the majority pointed
   and sharp, some very large and lanceolate. Eye large. Pectoral
   and ventral fins well developed; the rayed dorsal fin occupies
   the whole length of the back from the occiput to opposite the
   anal fin; adipose and anal fins of moderate size. Caudal forked.
   Branchiostegals six or seven.

  [Illustration: Fig. 270.--Plagyodus ferox.]

This is one of the largest and most formidable deep-sea fishes. One
species only is well known, _P. ferox_, from Madeira and the sea
off Tasmania; other species have been noticed from Cuba and the
North Pacific, but it is not evident in what respects they differ
specifically from _P. ferox_. This fish grows to a length of six feet,
and from the stomach of one example have been taken several Octopods,
Crustaceans, Ascidians, a young Brama, twelve young Boar-fishes,
a Horse-mackerel, and one young of its own species. The stomach is
coecal; the commencement of the intestine has extremely thick walls,
its inner surface being cellular, like the lung of a reptile; a
pyloric appendage is absent. All the bones are extremely thin, light,
and flexible, containing very little earthy matter; singular is the
development of a system of abdominal ribs, symmetrically arranged on
both sides, and extending the whole length of the abdomen. Perfect
specimens are rarely obtained on account of the want of coherence of
the muscular and osseous parts, caused by the diminution of pressure
when the fish reaches the surface of the water. The exact depth at
which _Plagyodus_ lives is not known; probably it never rises above a
depth of 300 fathoms.

The other less important genera belonging to this family are _Aulopus_,
_Chlorophthalmus_, _Scopelosaurus_, _Odontostomus_, and _Nannobrachium_.

  [Illustration: Fig. 271.--Pharyngeal bones and teeth of the
  Bream, Abramis brama.]


                       THIRD FAMILY--CYPRINIDÆ.

_Body generally covered with scales; head naked. Margin of the upper
jaw formed by the intermaxillaries. Belly rounded, or, if trenchant,
without ossifications. No adipose fin. Stomach without blind sac.
Pyloric appendages none. Mouth toothless; lower pharyngeal bones
well developed, falciform, sub-parallel to the branchial arches,
provided with teeth, which are arranged in one, two, or three series.
Air-bladder large, divided into an anterior and posterior portion by a
constriction, or into a right or left portion, enclosed in an osseous
capsule. Ovarian sacs closed._

The family of “Carps” is the one most numerously represented in the
fresh waters of the Old World and of North America. Also numerous
fossil remains are found in tertiary freshwater-formations, as in the
limestones of Oeningen and Steinheim, in the lignites of Bonn, Stöchen,
Bilin, and Ménat, in the marl slates and carbonaceous shales of
Licata in Sicily, and of Padang in Sumatra, in corresponding deposits
of Idaho in North America. The majority can be referred to existing
genera: _Barbus_, _Thynnichthys_, _Gobio_, _Leuciscus_, _Tinca_,
_Amblypharyngodon_, _Rhodeus_, _Cobitis_, _Acanthopsis_, only a few
showing characters different from those of living genera: _Cyclurus_,
_Hexapsephus_, _Mylocyprinus_ (tertiary of North America).

Most Carps feed on vegetable and animal substances; a few only are
exclusive vegetable feeders. There is much less diversity of form and
habits in this family than in the Siluroids; however, the genera are
sufficiently numerous to demand a further subdivision of the family
into groups.

I. CATOSTOMINA.--_Pharyngeal teeth in a single series, exceedingly
numerous and closely set. Dorsal fin elongate, opposite to the
ventrals; anal short, or of moderate length. Barbels none._

These fishes are abundant in the lakes and rivers of North America,
more than thirty species having been described, and many more named,
by American ichthyologists. Two species are known from North-Eastern
Asia. They are generally called “Suckers,” but their vernacular
nomenclature is very arbitrary and confused. Some of the species
which inhabit the large rivers and lakes grow to a length of three
feet and a weight of fifteen pounds. The following genera may be
distinguished:--_Catostomus_, “Suckers,” “Red-horses,” “Stone-rollers,”
“White Mullets;” _Moxostoma_; _Sclerognathus_, “Buffaloes,” “Black
Horses;” and _Carpiodes_, “Spear-fish,” “Sail-fish.”

II. CYPRININA.--_Anal fin very short, with not more than five or six,
exceptionally seven, branched rays. Dorsal fin opposite ventrals.
Abdomen not compressed. Lateral line running along the median line
of the tail. Mouth frequently with barbels, never more than four in
number. Pharyngeal teeth generally in a triple series in the Old World
genera; in a double or single series in the North American forms, which
are small and feebly developed. Air-bladder present, without osseous
covering._

   CYPRINUS.--Scales large. Dorsal fin long, with a more or less
   strong serrated osseous ray; anal short. Snout rounded, obtuse,
   mouth anterior, rather narrow. Pharyngeal teeth, 3. 1. 1.-1. 1.
   3, molar-like. Barbels four.

  [Illustration: Fig. 272.--The Carp, Cyprinus carpio.]

The “Carp” (_C. carpio_, “Karpfen,” “La carpe,”) is originally a
native of the East, and abounds in a wild state in China, where it
has been domesticated for many centuries; thence it was transported
to Germany and Sweden, and the year 1614 is assigned as the date of
its first introduction into England. It delights in tranquil waters,
preferring such as have a muddy bottom, and the surface partially
shaded with plants. Its food consists of the larvæ of aquatic insects,
minute testacea, worms, and the tender blades and shoots of plants. The
leaves of lettuce, and other succulent plants of a similar kind, are
said to be particularly agreeable to them, and to fatten them sooner
than any other food. Although the Carp eats with great voracity when
its supply of aliment is abundant, it can subsist for an astonishing
length of time without nourishment. In the winter, when the Carps
assemble in great numbers, and bury themselves among the mud and the
roots of plants, they often remain for many months without eating. They
can also be preserved alive for a considerable length of time out of
the water, especially if care be taken to moisten them occasionally
as they become dry. Advantage is often taken of this circumstance to
transport them alive, by packing them among damp herbage or damp linen;
and the operation is said to be unattended with any risk to the animal,
especially if the precaution be taken to put a piece of bread in its
mouth steeped in brandy!

The fecundity of these fishes is very great, and their numbers
consequently would soon become excessive but for the many enemies by
which their spawn is destroyed. No fewer than 700,000 eggs have been
found in the ovaries of a single Carp, and that, too, by no means an
individual of the largest size. Their growth is very rapid, more so
perhaps than that of any other Freshwater fish, and the size which they
sometimes attain is very considerable. In certain lakes in Germany
individuals are occasionally taken weighing thirty or forty pounds; and
Pallas relates that they occur in the Volga five feet in length, and
even of greater weight than the examples just alluded to. The largest
of which we have any account is that mentioned by Bloch, taken near
Frankfort-on-the-Oder, which weighed seventy pounds, and measured
nearly nine feet in length,--a statement the accuracy of which is very
much open to doubt.

Like other domesticated animals the Carp is subject to variation; some
individuals, especially when they have been bred under unfavourable
circumstances, have a lean and low body; others are shorter and higher.
Some have lost every trace of scales, and are called “Leather-carps;”
others retain them along the lateral line and on the back only
(“Spiegelkarpfen” of the Germans). Finally, in some are the fins much
prolonged, as in certain varieties of the Gold-fish. Cross-breeds
between the Carp and the Crucian Carp are of common occurrence.
The Carp is much more esteemed as food in inland countries than in
countries where the more delicate kinds of sea fishes can be obtained.

   CARASSIUS differs from _Cyprinus_ in lacking barbels; its
   pharyngeal teeth are compressed, in a single series, 4–4.

Two well-known species belong to this genus. The “Crucian Carp” (_C.
carassius_, “Karausche”) is generally distributed over Central and
Northern Europe, and extends into Italy and Siberia. It inhabits
stagnant waters only, and is so tenacious of life that it will
survive a lengthened sojourn in the smallest pools, where, however,
it remains stunted; whilst in favourable localities it attains to a
length of twelve inches. It is much subject to variation of form; very
lean examples are commonly called “Prussian Carps.” Its usefulness
consists in keeping ponds clean from a super-abundance of vegetable
growth, and in serving as food for other more esteemed fishes. The
second species is the “Gold-fish,” _Carassius auratus_. It is of very
common occurrence in a wild state in China and the warmer parts of
Japan, being entirely similar in colour to the Crucian Carp. In a
domesticated state it loses the black or brown chromatophors, and
becomes of a golden-yellow colour; perfect Albinos are comparatively
scarcer. Many varieties and monstrosities have been produced during
the long period of its domestication; the variety most highly priced
at present being the so-called “Telescope-fish,” of which a figure is
annexed. The Gold-fish is said to have been first brought to England
in the year 1691, and is now distributed over nearly all the civilised
parts of the world.

  [Illustration: Fig. 273.--Cyprinus auratus, var.]

   CATLA.--Scales of moderate size. Dorsal fin without osseous ray,
   with more than nine branched rays, commencing nearly opposite to
   the ventrals. Snout broad, with the integuments very thin; there
   is no upper lip, the lower with a free continuous posterior
   margin. Symphysis of the mandibulary bones loose, with prominent
   tubercles. Mouth anterior. Barbels none. Gill-rakers very long,
   fine, and closely set. Pharyngeal teeth, 5. 3. 2.-2. 3. 5.

The “Catla” (_C. buchanani_), one of the largest Carps of the Ganges,
growing to a length of more than three feet, and esteemed as food.

   LABEO.--Scales of moderate or small size. Dorsal fin without
   osseous ray, with more than nine branched rays, commencing
   somewhat in advance of the ventrals. Snout obtusely rounded,
   the skin of the maxillary region being more or less thickened,
   forming a projection beyond the mouth. Mouth transverse,
   inferior, with the lips thickened, each or one of them being
   provided with an inner transverse fold, which is covered with a
   deciduous horny substance forming a sharp edge, which, however,
   does not rest upon the bone as base, but is soft and movable.
   Barbels very small, two or four; the maxillary barbels more or
   less hidden in a groove behind the angle of the mouth. Anal
   scales not enlarged. Pharyngeal teeth uncinate, 5. 4. 2.-2. 4.
   5. Snout generally more or less covered with hollow tubercles.

About thirteen species are known from rivers of tropical Africa and the
East Indies.

   DISCOGNATHUS.--Scales of moderate size. Dorsal fin without
   osseous ray, with not more than nine branched rays, commencing
   somewhat in advance of the ventrals. Snout obtusely rounded,
   more or less depressed, projecting beyond the mouth, more or
   less tubercular. Mouth inferior, transverse, crescent-shaped;
   lips broad, continuous, with an inner sharp edge of the jaws,
   covered with horny substance on the lower jaw; upper lip more
   or less distinctly fringed; lower lip modified into a suctorial
   disk, with free anterior and posterior margins. Barbels two or
   four; if two, the upper are absent. Anal scales not enlarged.
   Pectoral fins horizontal. Pharyngeal teeth, 5. 4. 2.-2. 4. 5.

A small fish (_D. lamta_), extremely abundant in almost all the
mountain streams from Abyssinia and Syria to Assam.

   CAPOËTA.--Scales small, of moderate or large size. Dorsal fin
   with or without a strong osseous ray, with not more than nine
   branched rays. Snout rounded, with the mouth transverse and at
   its lower side; each mandible angularly bent inwards in front,
   the anterior mandibular edge being nearly straight, sharpish,
   and covered with a horny brown layer. No lower labial fold.
   Barbels two (rarely four), or entirely absent. Anal scales not
   conspicuously enlarged. Pharyngeal teeth compressed, truncated,
   5 or 4. 3. 2–2. 3. 4 or 5.

Characteristic of the fauna of Western Asia; one species from
Abyssinia. Of the fifteen species known _C. damascina_ deserves to
be specially mentioned, being abundant in the Jordan and other rivers
of Syria and Asia Minor.

   BARBUS.--Scales of small, moderate, or large size. Dorsal
   fin generally with the (third) longest simple ray ossified,
   enlarged, and frequently serrated; never, or only exceptionally,
   with more than nine branched rays, commencing opposite or nearly
   opposite to the root of the ventral fin. Eyes without adipose
   eyelid. Anal fin frequently very high. Mouth arched, without
   inner folds, inferior or anterior; lips without horny covering.
   Barbels short, four, two, or none. Anal scales not enlarged.
   Pharyngeal teeth 5. 4 or 3. 3 or 2.-2 or 3. 3 or 4. 5. Snout but
   rarely with tubercles or pore-like grooves.

No other genus of Cyprinoids is composed of so many species as the
genus of “Barbels,” about 200 being known from the tropical and
temperate parts of the Old World; it is not represented in the New
World. Although the species differ much from each other in the form of
the body, number of barbels, size of the scales, strength of the first
dorsal ray or spine, etc., the transition between the extreme forms is
so perfect that no further generic subdivision should be attempted.
Some attain a length of six feet, whilst others never exceed a length
of two inches. The most noteworthy are the large Barbels of the Tigris
(_B. subquincunciatus_, _B. esocinus_, _B. scheich_, _B. sharpeyi_);
the common Barbel of Central Europe and Great Britain (_B. vulgaris_);
the “Bynni” of the Nile (_B. bynni_); _B. canis_ from the Jordan; the
“Mahaseer” of the mountain streams of India (_B. mosal_), probably the
largest of all species, the scales of which are sometimes as large as
the palm of a hand. The small, large-scaled species are especially
numerous in the East Indies and the fresh waters of Tropical Africa.

   THYNNICHTHYS.--Scales small. Dorsal fin without an osseous
   ray, with not more than nine branched rays, commencing nearly
   opposite the ventrals. Head large, strongly compressed; eye
   without well-developed adipose membrane, in the middle of
   the depth of the head. Snout with the integuments very thin;
   there is no upper lip, and the lower jaw has a thin labial
   fold on the sides only. Mouth anterior and lateral; barbels
   none. Gill-rakers none; laminæ branchiales long, half as long
   as the post-orbital portion of the head; pseudobranchiæ none.
   Pharyngeal teeth lamelliform, with flat oblong crown, 5. 3 or 4.
   2–2. 4 or 3. 5, the teeth of the three series being wedged into
   one another.

Three species from the East Indies.

   OREINUS.--Scales very small. Dorsal fin with a strong osseous
   serrated ray, opposite to the ventrals. Snout rounded, with the
   mouth transverse, and at its lower side; mandibles broad, short,
   and flat, loosely joined together; margin of the jaw covered
   with a thick horny layer; a broad fringe-like lower lip, with
   free posterior margin. Barbels four. Vent and anal fin in a
   sheath, covered with enlarged tiled scales. Pharyngeal teeth
   pointed, more or less hooked, 5. 3. 2–2. 3. 5.

Three species from mountain streams of the Himalayas.

   SCHIZOTHORAX.--Hill-barbels, with the same singular sheath on
   each side of the vent, as in the preceding genus; but they
   differ in having the mouth normally formed, with mandibles of
   the usual length and width.

Seventeen species are known from fresh waters of the Himalayas, and
north of them. Other genera from the same region, and with the anal
sheath, are _Ptychobarbus_, _Gymnocypris_, _Schizopygopsis_, and
_Diptychus_.

   GOBIO.--Scales of moderate size; lateral line present. Dorsal
   fin short, without spine. Mouth inferior; mandible not
   projecting beyond the upper jaw when the mouth is open; both
   jaws with simple lips; a small but very distinct barbel at the
   angle of the mouth, quite at the extremity of the maxillary.
   Gill-rakers very short; pseudobranchiæ. Pharyngeal teeth, 5. 3
   or 2.--2 or 3. 5, hooked at the end.

The “Gudgeons” are small fishes of clear fresh waters of Europe;
they are, like the barbels, animal feeders. In Eastern Asia they
are represented by two closely allied genera, _Ladislavia_ and
_Pseudogobio_.

   CERATICHTHYS.--Scales of moderate or small size; lateral line
   present. Dorsal fin short, without spine, not or but slightly
   in advance of the ventrals. Mouth subinferior; the lower jaw
   does not project beyond the upper when the mouth is open;
   intermaxillaries protractile from below the maxillaries; both
   jaws with thickish lips; a small barbel at the angle of the
   mouth, quite at the extremity of the maxillary. Gill-rakers very
   short and few in number: pseudobranchiæ. Pharyngeal teeth 4–4.
   hooked at the end (sometimes 4, 1--1. 4).

About ten species are known from North America; they are small, and
called “Chub” in the United States. _C. biguttatus_ is, perhaps,
the most widely-diffused Freshwater-fish in the United States, and
common everywhere. Breeding males have generally a red spot on each
side of the head.

Other similar genera from the fresh waters of North America, and
generally called “Minnows,” are _Pimephales_ (the “Black Head”),
_Hyborhynchus_, _Hybognathus_, _Campostoma_ (the “Stone-lugger”),
_Ericymba_, _Cochlognathus_, _Exoglossum_ (the “Stone Toter” or
“Cut-lips”), and _Rhinichthys_ (the “Long-nosed Dace”).

The remaining Old World genera belonging to the group _Cyprinina_ are
_Cirrhina_, _Dangila_, _Osteochilus_, _Barynotus_, _Tylognathus_,
_Abrostomus_, _Crossochilus_, _Epalzeorhynchus_, _Barbichthys_,
_Amblyrhynchichthys_, _Albulichthys_, _Aulopyge_, _Bungia_, and
_Pseudorasbora_.

III. ROHTEICHTHYINA.--_Anal fin very short, with not more than six
branched rays. Dorsal fin behind ventrals. Abdomen compressed. Lateral
line running along the median line of the tail. Mouth without barbels.
Pharyngeal teeth in a triple series._

One genus and species only, _Rohteichthys microlepis_, from Borneo and
Sumatra.

IV. LEPTOBARBINA.--_Anal fin very short, with not more than six
branched rays. Dorsal fin opposite to ventrals. Abdomen not compressed.
Lateral line running in the lower half of the tail. Barbels present,
not more than four in number. Pharyngeal teeth in a triple series._

One genus and species only, _Leptobarbus hoevenii_, from Borneo and
Sumatra.

V. RASBORINA.--_Anal fin very short, with not more than six branched
rays. Dorsal fin inserted behind the origin of the ventrals. Abdomen
not compressed. Lateral line running along the lower half of the
tail, if complete. Mouth sometimes with barbels, which are nevermore
than four in number. Pharyngeal teeth in a triple, or single series.
Air-bladder present, without osseous covering._

   RASBORA.--Scales large, or of moderate size, there being
   generally four and a half longitudinal series of scales between
   the origin of the dorsal fin and the lateral line, and one
   between the lateral line and the ventral. Lateral line curved
   downwards. Dorsal fin with seven or eight branched rays, not
   extending to above the anal, which is seven-rayed. Mouth of
   moderate width, extending to the front margin of the orbit,
   with the lower jaw slightly prominent, and provided with three
   prominences in front, fitting into grooves of the upper jaw;
   barbels none, in one species two. Gill-rakers short, lanceolate.
   Pseudobranchiæ. Pharyngeal teeth in three series, uncinate.

Thirteen species of small size from the East Indian Continent and
Archipelago, and from rivers on the east coast of Africa.

   AMBLYPHARYNGODON.--Scales small; lateral line incomplete. Dorsal
   fin without an osseous ray, with not more than nine branched
   rays, commencing a little behind the origin of the ventrals.
   Head of moderate size, strongly compressed; eye without adipose
   membrane; snout with the integuments very thin; there is no
   upper lip, and the lower jaw has a short labial fold on the
   sides only. Mouth anterior, somewhat directed upwards, with
   the lower jaw prominent. Barbels none. Gill-rakers extremely
   short; pseudobranchiæ. Pharyngeal teeth molar-like, with their
   crowns concave, 3. 2. 1.--1. 2. 3. Intestinal tract narrow, with
   numerous convolutions.

Three species of small size from the Continent of India.

To the same group belong _Luciosoma_, _Nuria_, and _Aphyocypris_, from
the same geographical region.

VI. SEMIPLOTINA.--_Anal fin short, with seven branched rays, not
extending forwards to below the dorsal. Dorsal fin elongate, with an
osseous ray. Lateral line running along the middle of the tail. Mouth
sometimes with barbels._

Two genera: _Cyprinion_, from Syria and Persia, and _Semiplotus_ from
Assam.

VII. XENOCYPRIDINA.--_Anal fin rather short, with seven or more
branched rays, not extending forwards to below the dorsal fin. Dorsal
short, with an osseous ray. Lateral line running along the middle of
the tail. Mouth sometimes with barbels. Pharyngeal teeth in a triple or
double series._

Three genera: _Xenocypris_ and _Paracanthobrama_ from China; and
_Mystacoleucus_ from Sumatra.

VIII. LEUCISCINA.--_Anal fin short or of moderate length, with from
eight to eleven branched rays, not extending forwards to below the
dorsal. Dorsal fin short, without osseous ray. Lateral line, if
complete, running along, or nearly in, the middle of the tail. Mouth
generally without barbels. Pharyngeal teeth in a single or double
series._

   LEUCISCUS.--Body covered with imbricate scales. Dorsal fin
   commencing opposite, rarely behind, the ventrals. Anal fin
   generally with from nine to eleven, rarely with eight (in small
   species only), and still more rarely with fourteen rays. Mouth
   without structural peculiarities; lower jaw not trenchant;
   barbels none. Pseudobranchiæ. Pharyngeal teeth conical or
   compressed, in a single or double series. Intestinal tract
   short, with only a few convolutions.

The numerous species of this genus are comprised under the name of
“White-fish;” they are equally abundant in the northern temperate
zone of both hemispheres, about forty species being known from the
Old World, and about fifty from the New. The most noteworthy species
of the former Fauna are the “Roach” (_L. rutilus_, see Fig. 21,
p. 50), common all over Europe north of the Alps; the “Chub” (_L.
cephalus_), extending into Northern Italy and Asia Minor; the “Dace”
(_L. leuciscus_), a companion of the Roach; the “Id” or “Nerfling” (_L.
idus_), from the central and northern parts of Continental Europe,
domesticated in some localities of Germany, in this condition assuming
the golden hue of semi-albinism, like a Gold-fish, and then called the
“Orfe;” the “Rudd,” or “Red-eye” (_L. erythrophthalmus_), distributed
all over Europe and Asia Minor, and distinguished by its scarlet lower
fins; the “Minnow” (_L. phoxinus_), abundant everywhere in Europe, and
growing to a length of seven inches in favourable localities. The North
American species are much less perfectly known; the smaller ones are
termed “Minnows,” the larger “Shiner” or “Dace.” The most common are
_L. cornutus_ (Red-fin, Red Dace); _L. neogæus_, a minnow resembling
the European species, but with incomplete lateral line; _L. hudsonius_,
the “Spawn-eater” or “Smelt.”

   TINCA.--Scales small, deeply embedded in the thick skin; lateral
   line complete. Dorsal fin short, its origin being opposite the
   ventral fin; anal short; caudal subtruncated. Mouth anterior;
   jaws with the lips moderately developed; a barbel at the angle
   of the mouth. Gill-rakers short, lanceolate; pseudobranchiæ
   rudimentary. Pharyngeal teeth 4 or 5.-5, cuneiform, slightly
   hooked at the end.

  [Illustration: Fig. 274.--The Tench (Tinca tinca).]

Only one species of “Tench” is known (_T. tinca_), found all over
Europe in stagnant waters with soft bottom. The “Golden Tench” is only
a variety of colour, an incipient albinism like the Gold-fish and Id.
Like most other Carps of this group it passes the winter in a state of
torpidity, during which it ceases to feed. It is extremely prolific,
297,000 ova having been counted in one female; its spawn is of a
greenish colour.

   LEUCOSOMUS.--Scales of moderate or small size; lateral line
   present. Dorsal fin commencing opposite, or nearly opposite, to
   the ventral. Anal fin short. Mouth anterior or sub-anterior;
   intermaxillaries protractile. A very small barbel at the
   extremity of the maxillary. Lower jaw with rounded margin, and
   with the labial folds well developed laterally. Gill-rakers
   short; pseudobranchiæ. Pharyngeal teeth in a double series.

A North American genus, to which belong some of the most common species
of the United States. _L. pulchellus_ (the “Fall-fish,” “Dace,” or
“Roach”), one of the largest White-fishes of the Eastern States,
attaining to a length of 18 inches, and abundant in the rapids of the
larger rivers. _L. corporalis_ (the “Chub”), common everywhere from New
England to the Missouri region.

   CHONDROSTOMA.--Scales of moderate size or small. Lateral line
   terminating in the median line of the depth of the tail. Dorsal
   fin with not more than nine branched rays, inserted above the
   root of the ventrals. Anal fin rather elongate, with ten or more
   rays. Mouth inferior, transverse, lower jaw with a cutting edge,
   covered with a brown horny layer. Barbels none. Gill-rakers
   short, fine; pseudobranchiæ. Pharyngeal teeth 5 or 6 or 7.-7 or
   6 or 5, knife-shaped, not denticulated. Peritoneum black.

Seven species from the Continent of Europe and Western Asia.

Other Old World genera belonging to the _Leuciscina_ are _Myloleucus_,
_Ctenopharyngodon_, and _Paraphoxinus_; from North America:
_Mylopharodon_, _Meda_, _Orthodon_, and _Acrochilus_.

IX. RHODEINA.--_Anal fin of moderate length, with from nine to twelve
branched rays, extending forwards to below the dorsal. Dorsal fin
short, or of moderate length. Lateral line, if complete, running along
or nearly in the middle of the tail. Mouth with very small, or without
any barbels. Pharyngeal teeth in a single series._

Very small roach-like fishes inhabiting chiefly Eastern Asia and Japan,
one species (_Rh. amarus_) advancing into Central Europe. The thirteen
species known have been distributed among four genera, _Achilognathus_,
_Acanthorhodeus_, _Rhodeus_, and _Pseudoperilampus_. In the females a
long external urogenital tube is developed annually during the spawning
season. The European species is known in Germany by the name of
“Bitterling.”

X. DANIONINA.--_Anal fin of moderate length or elongate, with not less,
and generally more, than eight branched rays. Lateral line running
along the lower half of the tail. Mouth with small, or without any,
barbels. Abdomen not trenchant. Pharyngeal teeth in a triple or double
series._

Small fishes from the East Indian Continent, Ceylon, the East Asiatic
Islands, and a few from East African Rivers, The genera belonging to
this group are _Danio_, _Pteropsarion_, _Aspidoparia_, _Barilius_,
_Bola_, _Scharca_, _Opsariichthys_, _Squaliobarbus_, and _Ochetobus_:
altogether about forty species.

XI. HYPOPHTHALMICHTHYINA.--_Anal fin elongate. Lateral line running
nearly along the median line of the tail. Mouth without barbels.
Abdomen not trenchant. No dorsal spine. Pharyngeal teeth in a single
series._

One genus (_Hypophthalmichthys_) with two species from China.

XII. ABRAMIDINA.--_Anal fin elongate. Abdomen, or part of the abdomen,
compressed._

  [Illustration: Fig. 275.--The Bream (Abramis brama).]

   ABRAMIS.--Body much compressed, elevated, or oblong. Scales
   of moderate size. Lateral line present, running in the lower
   half of the tail. Dorsal fin short, with spine, opposite to the
   space between ventrals and anals. Lower jaw generally shorter,
   and rarely longer than the upper. Both jaws with simple lips,
   the lower labial fold being interrupted at the symphysis of
   the mandible. Upper jaw protractile. Gill-rakers rather short;
   pseudobranchiæ. The attachment of the branchial membrane to the
   isthmus takes place at some distance behind the vertical from
   the orbit. Pharyngeal teeth in one or two series, with a notch
   near the extremity. Belly behind the ventrals compressed into an
   edge, the scales not extending across it.

The “Breams” are represented in the temperate parts of both northern
hemispheres; in Europe there occur the “Common Bream,” _A. brama_;
the “Zope,” _A. ballerus_; _A. sapa_; the “Zärthe,” _A. vimba_; _A.
elongatus_; the “White Bream,” _A. blicca_; _A. bipunctatus_. Of these
_A. brama_ and _A. blicca_ are British; the former being one of the
most common fishes, and sometimes attaining to a length of two feet.
Crosses between these two species, and even with other Cyprinoids, are
not rare. Of the American species _A. americanus_ (“Shiner,” “Bream”)
is common and widely distributed; like the European Bream it lives
chiefly in stagnant waters or streams with a slow current.

   ASPIUS.--Body oblong; scales of moderate size; lateral line
   complete, terminating nearly in the middle of the depth of the
   tail. Dorsal fin short, without spine, opposite to the space
   between the ventrals and anal; anal fin elongate, with thirteen
   or more rays. Lower jaw more or less conspicuously projecting
   beyond the upper. Lips thin, simple, the lower labial fold being
   at the symphysis; upper jaw but little protractile. Gill-rakers
   short and widely set; pseudobranchiæ. The attachment of the
   branchial membrane to the isthmus takes place below the hind
   margin of the orbit. Pharyngeal teeth hooked, 5. 3.-3 or 2. 5 or
   4. Belly behind the ventrals compressed, the scales covering the
   edge.

Four species from Eastern Europe to China.

   ALBURNUS.--Body more or less elongate; scales of moderate size;
   lateral line present, running below the median line of the
   tail. Dorsal fin short, without spine, opposite to the space
   between ventrals and anal; anal fin elongate, with more than
   thirteen rays. Lower jaw more or less conspicuously projecting
   beyond the upper. Lips thin, simple, the lower labial fold
   being interrupted at the symphysis of the mandible. Upper jaw
   protractile. Gill-rakers slender, lanceolate, closely set;
   pseudobranchiæ. The attachment of the branchial membrane to
   the isthmus takes place below the hind margin of the orbit.
   Pharyngeal teeth in two series, hooked. Belly behind the
   ventrals compressed into an edge, the scales not extending
   across it.

“Bleak” are numerous in Europe and Western Asia, fifteen species
being known. The common Bleak (_A. alburnus_) is found north of the
Alps only, and represented by another species (_A. alburnellus_,
“Alborella,” or “Avola”) in Italy.

Of the other genera referred to this group, _Leucaspius_ and _Pelecus_
belong to the European Fauna; _Pelotrophus_ is East African; all
the others occur in the East Indies or the temperate parts of
Asia, viz. _Rasborichthys_, _Elopichthys_, _Acanthobrama_ (Western
Asia), _Osteobrama_, _Chanodichthys_, _Hemiculter_, _Smiliogaster_,
_Toxabramis_, _Culter_, _Eustira_, _Chela_, _Pseudolabuca_, and
_Cachius_.

XIII. HOMALOPTERINA.--_Dorsal and anal fins short, the former opposite
to ventrals. Pectoral and ventral fins horizontal, the former with the
outer rays simple. Barbels six or none. Air-bladder absent. Pharyngeal
teeth in a single series, from ten to sixteen in number._

Inhabitants of hill-streams in the East Indies; they are of small size
and abundant where they occur. Thirteen species are known belonging
to the genera _Homaloptera_, _Gastromyzon_, _Crossostoma_, and
_Psilorhynchus_.

XIV. COBITIDINA.--_Mouth surrounded by six or more barbels. Dorsal fin
short or of moderate length; anal fin short. Scales small, rudimentary,
or entirely absent. Pharyngeal teeth in a single series, in moderate
number. Air-bladder partly or entirely enclosed in a bony capsule.
Pseudobranchiæ none_: Loaches.

   MISGURNUS.--Body elongate, compressed. No sub-orbital spine. Ten
   or twelve barbels, four belonging to the mandible. Dorsal fin
   opposite to the ventrals; caudal rounded.

Four species from Europe and Asia. _M. fossilis_ is the largest
of European Loaches, growing to a length of ten inches; it occurs in
stagnant waters of eastern and southern Germany and northern Asia.
In China and Japan it is replaced by an equally large species, _M.
anguillicaudatus_.

   NEMACHILUS.--No erectile sub-orbital spine. Six barbels, none at
   the mandible. Dorsal fin opposite to the ventrals.

The greater number of Loaches belong to this genus; about fifty species
are known from Europe and temperate Asia; such species as extend
into tropical parts inhabit streams of high altitudes. Loaches are
partial to fast-running streams with stony bottom, and exclusively
animal feeders. In spite of their small size they are esteemed as food
where they occur in sufficient abundance. The British species, _N.
barbatulus_, is found all over Europe except Denmark and Scandinavia.

   COBITIS.--Body more or less compressed, elongate; back not
   arched. A small, erectile, bifid sub-orbital spine below the
   eye. Six barbels only on the upper jaw. Dorsal fin inserted
   opposite to ventrals. Caudal rounded or truncate.

Only three species are known, of which _C. tænia_ occurs in Europe. It
is scarce and very local in Great Britain.

   BOTIA.--Body compressed, oblong; back more or less arched. Eyes
   with a free circular eyelid; an erectile bifid sub-orbital
   spine. Six barbels on the upper jaw, sometimes two others at the
   mandibulary symphysis. Dorsal fin commencing in advance of the
   root of the ventrals; caudal fin forked. Air-bladder consisting
   of two divisions: the anterior enclosed in a partly osseous
   capsule, the posterior free, floating in the abdominal cavity.

  [Illustration: Fig. 276.--Botia rostrata. From Bengal.]

This genus is more tropical than any of the preceding, and the majority
of the species (eight in number) are finely coloured. The more elevated
form of their body, and the imperfect ossification of the capsules of
the air-bladder, the divisions of which are not side by side, but
placed in the longitudinal axis of the body, indicate likewise that
this genus is more adapted for still waters of the plains than for the
currents of hill-streams.

Other genera from tropical India are _Lepidocephalichthys_,
_Acanthopsis_, _Oreonectes_ (hills near Hong-Kong), _Paramisgurnus_
(Yan-tse-Kiang), _Lepidocephalus_, _Acanthophthalmus_, and _Apua_.


                       FOURTH FAMILY--KNERIIDÆ.

_Body scaly, head naked. Margin of the upper jaw formed by the
intermaxillaries. Dorsal and anal fins short, the former belonging
to the abdominal portion of the vertebral column. Teeth none, either
in the mouth or pharynx. Barbels none. Stomach siphonal; no pyloric
appendages. Pseudobranchiæ none. Branchiostegals three; air-bladder
long, not divided. Ovaries closed._

Small loach-like fishes from fresh waters of tropical Africa; two
species only, _Kneria angolensis_ and _K. spekii_, are known.


                      FIFTH FAMILY--CHARACINIDÆ.

_Body covered with scales, head naked; barbels none. Margin of the
upper jaw formed by the intermaxillaries in the middle and by the
maxillaries laterally. Generally a small adipose fin behind the dorsal.
Pyloric appendages more or less numerous; air-bladder transversely
divided into two portions, and communicating with the organ of hearing
by means of the auditory ossicles. Pseudobranchiæ none._

The fishes of this family are confined to the fresh waters of Africa,
and especially of tropical America, where they replace the Cyprinoids,
with which family, however, they have but little in common as far as
their structural characteristics are concerned. Their co-existence
in Africa with Cyprinoids proves only that that continent is nearer
to the original centre, from which the distribution of Cyprinoids
commenced than tropical America. The family includes herbivorous as
well as strictly carnivorous forms; some are toothless, whilst others
possess a most formidable dentition. The family contains so many
diversified forms as to render a subdivision into groups necessary.
They have not yet been obtained in fossiliferous strata.

I. ERYTHRININA.--_Adipose fin absent._

The sixteen species of this group belong to the fauna of tropical
America, and are referred to the genera _Macrodon_, _Erythrinus_,
_Lebiasina_, _Nannostomus_, _Pyrrhulina_, and _Corynopoma_.

II. CURIMATINA.--_A short dorsal and an adipose fin; dentition
imperfect. Tropical America._

   CURIMATUS.--Dorsal fin placed nearly in the middle of the body;
   anal rather short or of moderate length; ventrals below the
   dorsal. Body oblong or elevated, with the belly rounded or
   flattened before the ventrals. Cleft of the mouth transverse,
   lips none, margins of the jaws trenchant. No teeth whatever.
   Intestinal tract very long and narrow.

About twenty species are known, of rather small size.

The other genera of this group have teeth, but they are either
rudimentary or absent in some part of the jaws: _Prochilodus_,
_Cænotropus_, _Hemiodus_, _Saccodon_, _Parodon_.

III. CITHARININA.--_A rather long dorsal and an adipose fin; minute
labial teeth. Tropical Africa._

One genus only, _Citharinus_, with two species, is known. Common in the
Nile, attaining to a length of three feet.

IV. ANASTOMATINA.--_A short dorsal and an adipose fin; teeth in both
jaws well developed; the gill-membranes grown to the isthmus; nasal
openings remote from each other. Tropical America._

   LEPORINUS.--Dorsal fin placed nearly in the middle of the length
   of the body; anal short; ventrals below the dorsal. Body oblong,
   covered with scales of moderate size; belly rounded. Cleft of
   the mouth small, with the lips well developed; teeth in the
   intermaxillary and mandible, few in number, flattened, with the
   apex more or less truncated, and not serrated; the middle pair
   of teeth is the longest in both jaws; palate toothless.

This genus is generally distributed in the rivers east of the Andes;
about twenty species are known, some of which, like _L. frederici_, _L.
megalepis_, are very common. They are well marked by black bands or
spots, and rarely grow to a length of two feet, being generally much
smaller.--The other genera belonging to this group are _Anastomus_ and
_Rhytiodus_.

V. NANNOCHARACINA.--_A short dorsal and an adipose fin; teeth in both
jaws well developed; notched incisors. The gill-membranes are grown to
the isthmus. Nostrils close together._

One genus, _Nannocharax_, with two species only, from the Nile and
Gaboon; very small.

VI. TETRAGONOPTERINA.--_A short dorsal and an adipose fin; the teeth
in both jaws well developed, compressed, notched, or denticulated; the
gill-membranes free from the isthmus, and the nasal openings close
together. South America and Tropical Africa._

   ALESTES.--The dorsal fin is placed in the middle of the length
   of the body, above or behind the ventrals; anal fin rather
   long. Body oblong, covered with scales of moderate or large
   size; belly rounded. Cleft of the mouth rather small. Maxillary
   teeth none; intermaxillary teeth in two series; those of the
   front series more or less compressed, more or less distinctly
   tricuspid; the teeth of the hinder series are broad, molar-like,
   each armed with several pointed tubercles. Teeth in the
   lower jaw in two series; those in the front series laterally
   compressed, broader behind than in front; the hinder series is
   composed of two conical teeth. All the teeth are strong, few in
   number.

Fourteen species from Tropical Africa; several inhabit the Nile, of
which the “Raches” (_A. dentex_ and _A. kotschyi_) are the most common.

   TETRAGONOPTERUS.--The dorsal fin is placed in the middle
   of the length of the body, above or immediately behind the
   ventrals; anal fin long. Body oblong or elevated, covered with
   scales of moderate size; belly rounded. Cleft of the mouth of
   moderate width. Anterior teeth strong, lateral teeth small.
   Intermaxillary and mandibulary teeth subequal in size, with
   a compressed and notched crown, the former in a double, the
   latter in a single series; maxillary with a few teeth near its
   articulation, rarely with the entire edge denticulated.

Of all the genera of this family _Tetragonopterus_ is represented by
the greatest number of species; about fifty are known. Some of them
seem to have a very wide range, whilst others are merely local. All are
of small size, rarely exceeding a length of eight inches.

   CHIRODON.--Dorsal fin placed in the middle of the length of the
   body, behind the ventrals; anal long or of moderate length. Body
   oblong, covered with scales of moderate size; lateral line not
   continued to the tail. Belly rounded before the ventrals. Cleft
   of the mouth narrow, maxillary short. A single series of small
   serrated teeth in the intermaxillary and mandibulary; maxillary
   teeth none.

  [Illustration: Fig. 277.--Chirodon alburnus.]

Three species of small size from various parts of South America; the
species figured is represented of the natural size, and comes from the
Upper Amazons.

   MEGALOBRYCON.--Dorsal fin placed in middle of the length of
   the body, immediately behind the ventrals. Anal long. Abdomen
   rounded in front of, and somewhat compressed behind, the
   ventrals. Cleft of the mouth of moderate width. Teeth notched,
   in a triple series in the intermaxillary, and in a single in the
   maxillary and mandible; no other teeth behind the mandibulary
   teeth or on the palate. Scales of moderate size, with the free
   portion striated.

One species from the Upper Amazons (_M. cephalus_). Specimens more
than one foot long have been obtained.

  [Illustration: Fig. 278.--Megalobrycon cephalus.]

   GASTROPELECUS.--Dorsal fin placed behind the middle of the
   length of the body, above the anal; anal long; pectoral long;
   ventrals very small or rudimentary. Body strongly compressed,
   with the thoracic region dilated into a sub-semicircular disk.
   Scales of moderate size. Lateral line descending obliquely
   backwards towards the origin of the anal fin. The lower profile
   compressed into an acute ridge. Cleft of the mouth of moderate
   width; teeth compressed, tricuspid, in one or two series in the
   intermaxillary, and in a single in the mandible; maxillary with
   a few minute conical teeth; palate toothless.

Three specimens of this singular form are known from Brazil and the
Guyanas; they are of very small size.

The majority of the other genera belonging to this group are South
American, viz. Piabucina, Scissor, _Pseudochalceus_, _Aphyocharax_,
_Chalceus_, _Brycon_, _Chalcinopsis_, _Bryconops_, _Creagrutus_,
_Chalcinus_, _Piabuca_, _Paragoniates_, and _Agoniates_; two only
are African, viz. _Nannæthiops_, which represents the South American
_Tetragonopterus_, and _Bryconæthiops_, which is allied to Brycon.

VII. HYDROCYONINA.--_A short dorsal and an adipose fin_; _teeth in
both jaws well developed and conical; gill membranes free from the
isthmus; nasal openings close together. South America and Tropical
Africa. Fishes of prey._

   HYDROCYON.--The dorsal fin is in the middle of the length of the
   body, above the ventrals; anal of moderate length. Body oblong,
   compressed, covered with scales of moderate size; belly rounded.
   Cleft of the mouth wide, without lips; the intermaxillaries and
   mandibles are armed with strong pointed teeth, widely set and
   few in number; they are received in notches of the opposite
   jaw, and visible externally when the mouth is closed. Palate
   toothless. Cheeks covered with the enlarged sub-orbital bones.
   Orbit with an anterior and posterior adipose eyelid. Intestinal
   tract short.

Four species from Tropical Africa; two occur in the Nile, _H.
forskalii_ being abundant, and well known by the names “Kelb el
bahr” and “Kelb el moyeh.” Their formidable dentition renders them most
destructive to other fishes; they grow to a length of four feet.

   CYNODON.--Dorsal fin placed behind, or nearly in, the middle of
   the length of the body, behind the ventrals; anal long. Head
   and body compressed, oblong, the latter covered with very small
   scales; belly compressed, keeled. Teeth in the intermaxillary,
   maxillary, and mandible in a single series, conical, widely set,
   of unequal size; a pair of very large canine teeth anteriorly
   in the lower jaw, received in two grooves on the palate; palate
   with patches of minute granulated teeth. The outer branchial
   arch without gill-rakers, but with very short tubercles.

Four species from Brazil and the Guyanas; they are as formidable fishes
of prey as the preceding, and grow to the same size.

With the exception of _Sarcodaces_, all the remaining genera of this
group belong to the fauna of Tropical America, viz. _Anacyrtus_,
_Hystricodon_, _Salminus_, _Oligosarcus_, _Xiphorhamphus_, and
_Xiphostoma_.

VIII. DISTICHODONTINA.--_Dorsal fin rather elongate; adipose fin
present. Gill-membranes attached to the isthmus; belly rounded.
Tropical Africa._

The species, ten in number, belong to one genus only (_Distichodus_),
well known on the Nile under the name of “Nefasch.” They grow to a
considerable size, being sometimes four feet long and one and a half
foot deep. They are used as food.

IX. ICHTHYBORINA.--_An adipose fin; number of dorsal rays increased
(12–17); gill-membranes free from the isthmus. Belly rounded; canine
teeth. Tropical Africa._

Two genera only: _Ichthyborus_ from the Nile, and _Phago_ from West
Africa. Small fishes of very rare occurrence.

X. CRENUCHINA.--_Dorsal fin rather elongate; an adipose fin.
Gill-membranes free from the isthmus, with the belly rounded, and
without canine teeth._

This small group is represented in the Essequibo by a single species,
_Crenuchus spilurus_, and by another in West Africa, _Xenocharax
spilurus_.

XI. SERRASALMONINA.--_Dorsal fin rather elongate; an adipose fin.
Gill-membranes free from the isthmus; belly serrated. Tropical America._

Although the fishes of this family do not attain any considerable size,
the largest scarcely exceeding two feet in length, their voracity,
fearlessness, and number renders them a perfect pest in many rivers of
tropical America. In all, the teeth are strong, short, sharp, sometimes
lobed incisors, arranged in one or more series; by means of them
they cut off a mouthful of flesh as with a pair of scissors; and any
animal falling into the water where these fishes abound is immediately
attacked and cut in pieces in an incredibly short time. They assail
persons entering the water, inflicting dangerous wounds before the
victims are able to make their escape. In some localities it is
scarcely possible to catch fishes with the hook and line, as the fish
hooked is immediately attacked by the “Caribe” (as these fishes are
called), and torn to pieces before it can be withdrawn from the water.
The Caribes themselves are rarely hooked, as they snap the hook or
cut the line. The smell of blood is said to attract at once thousands
of these fishes to a spot. They are most abundant in the Brazils and
Guyanas; some forty species are known, and referred to the genera
_Mylesinus_, _Serrasalmo_, _Myletes_, and _Catoprion_.

  [Illustration: Fig. 279.--Serrasalmo scapularis, from the Essequibo.]


                     SIXTH FAMILY--CYPRINODONTIDÆ.

_Head and body covered with scales; barbels none. Margin of the upper
jaw formed by the intermaxillaries only. Teeth in both jaws; upper
and lower pharyngeals with cardiform teeth. Adipose fin none; dorsal
fin situated on the hinder half of the body. Stomach without blind
sac; pyloric appendages none. Pseudobranchiæ none; air-bladder simple,
without ossicula auditus._

Small fishes, inhabiting fresh, brackish, and salt water of Southern
Europe, Africa, Asia, and America. The majority are viviparous; and to
facilitate copulation the anal fin of the adult male of many species
is modified into a copulatory organ, which is probably (partially at
least) introduced into the vulva of the female; but it is uncertain
whether it serves to conduct the semen, or merely to give the male
a firmer hold of the female during the act. Also secondary sexual
differences are developed in the Cyprinodonts; the males are always
the smaller, sometimes several times smaller than the females, quite
diminutive; and they are perhaps the smallest fishes in existence. The
fins generally are more developed in the males, and the coloration is
frequently different also. Some species are carnivorous; others live
on the organic substances mixed with mud. Fossil remains have been
found in tertiary strata, all apparently referable to the existing
genus _Cyprinodon_; they occur near Aix in Provence, in the marl
of Gesso, St. Angelo, in the Brown coal near Bonn, near Frankfort,
and in the freshwater-chalk of Oeningen. In the latter locality a
_Poecilia_ occurs likewise.

The genera can be divided into two groups:

I. CYPRINODONTIDÆ CARNIVORÆ.--_The bones of each ramus of the mandible
are firmly united; intestinal tract short, or but little convoluted.
Carnivorous or insectivorous._

   CYPRINODON.--Cleft of the mouth small, developed laterally and
   horizontally. Snout short. Teeth of moderate size, incisor-like,
   notched, in a single series. Scales rather large. Origin of the
   anal fin behind that of the dorsal in both sexes, both fins
   being larger in the male than in the female. Anal not modified
   into a sexual organ.

Seven species occur in the Mediterranean region, all of which seem
able to live in briny springs or pools, the water of which contains a
much greater percentage of salts than sea-water, as the brine-springs
near the Dead Sea or in the Sahara. They are as little affected by
the high temperature of some of these springs (91°), for instance
of that at Sidi Ohkbar in the Sahara. Like other fishes living in
limited localities or concealing themselves in mud, Cyprinodonts lose
sometimes their ventral fins; such specimens have been described as
_Tellia_. The species of the New World are less known than those
of the Old, but not less numerous.

Allied to Cyprinodon are _Fitzroyia_ from Monte Video, and _Characodon_
from Central America.

   HAPLOCHILUS.--Snout flat, both jaws being much depressed, and
   armed with a narrow band of villiform teeth. Body oblong,
   depressed anteriorly, compressed posteriorly. Dorsal fin short,
   commencing behind the origin of the anal, which is more or less
   elongate.

Twenty species from the East Indies, tropical Africa, and temperate and
tropical America.

   FUNDULUS.--Cleft of the mouth of moderate width, developed
   laterally and horizontally. Snout of moderate length. Teeth
   in a narrow band, those of the outer series being largest,
   conical. Scales of moderate size. Dorsal fin commencing before
   or opposite the origin of the anal. Sexes not differentiated.

“Killifish,” abundant in the New World, where about twenty species have
been found; _F. heteroclitus_, _majalis_, _diaphanus_, being common on
the Atlantic coast of the United States; from the Old World two species
only are known, viz. _F. hispanicus_ from Spain, and _F. orthonotus_
from the east coast of Africa. Allied to _Fundulus_ are the South
American _Limnurgus_, _Lucania_, _Rivulus_, and _Cynolebias_.

   ORESTIAS.--Ventral fins none. Cleft of the mouth of moderate
   width, directed upwards, with the lower jaw prominent, and with
   the upper protractile. Both jaws with a narrow band Of small
   conical teeth. Scales rather small or of moderate size, those
   on the head and upper part of the trunk frequently enlarged,
   plate-like, and granulated. Dorsal and anal fins moderately
   developed, opposite to each other. Sexes not differentiated by
   modification of the anal fin. The gill-membranes of both sides
   are united for a short distance, and not attached to the isthmus.

Inhabitants of Lake Titicaca and other elevated sheets of water on the
Cordilleras of Peru and Bolivia, between the 14th and 19th degrees of
latitude, at an elevation of 13,000 and 14,000 feet above the level
of the sea. Singularly, the fishes of this outlying genus attain to a
greater size than any other members of this family, being about eight
inches long and comparatively bulky. They are considered a delicacy.
Six species.

   JENYNSIA.--Cleft of the mouth small, developed laterally and
   horizontally; snout not produced. Both jaws with a series of
   tricuspid teeth of moderate size. Scales of moderate size.
   The origin of the anal fin is, in both sexes, behind that of
   the dorsal, although the anal of the male is modified into an
   intromittent organ, in which scarcely any of the rays remain
   distinct.

One species from Maldonado.

  [Illustration: Fig. 280.--Gambusia punctata, from Cuba. A. Male;
  B. Female.]

   GAMBUSIA.--Cleft of the mouth developed laterally and
   horizontally. Snout not produced, with the lower jaw more or
   less prominent. Both jaws with a band of teeth, those of the
   outer series being strongest and conical. Scales rather large.
   Origin of the anal fin more or less in advance of that of the
   dorsal. Anal fin of the male modified into an intromittent organ
   and much advanced.

Eight species from the West Indies and the southern parts of South
America.--Allied genera are the Central American _Pseudoxiphophorus_
and _Belonesox_.

   ANABLEPS.--Head broad and depressed, with the supraorbital
   part very much raised. Body elongate, depressed anteriorly
   and compressed posteriorly. Cleft of the mouth horizontal, of
   moderate width, the mandible being short; upper jaw protractile.
   Both jaws armed with a band of villiform teeth, those of the
   outer series being largest and somewhat movable. The integuments
   of the eye are divided into an upper and lower portion by a
   dark-coloured transverse band of the conjunctiva; also the pupil
   is completely divided into two by a pair of lobes projecting
   from each side of the iris. Scales rather small or of moderate
   size. Dorsal and anal fins short, the former behind the latter.
   The anal fin of the male is modified into a thick and long scaly
   conical organ with an orifice at its extremity.

Three species from tropical America. They are the longest Cyprinodonts,
attaining to the length of nearly twelve inches. Their peculiar habit
of swimming with part of the head out of the water has been noticed
above (p. 113).

II. CYPRINODONTIDÆ LIMNOPHAGÆ.--_The bones of each ramus of the
mandible are but loosely joined; intestinal tract with numerous
circumvolutions. Sexes differentiated. Mud-eating. Tropical America._

   POECILIA.--Cleft of the mouth small, transverse; mandible very
   short. Both jaws with a narrow band of minute teeth. Scales
   rather large. Origin of the anal fin generally nearly opposite
   to that of the dorsal fin in the female, but in the male it is
   modified into an intromittent organ and much advanced. Dorsal
   fin short, with not more than eleven rays.

Sixteen species.

   MOLLIENESIA.--Differing from _Poecilia_ in having a larger
   dorsal fin, with twelve or more rays.

Five species. The males are most beautifully coloured, and their
dorsal fin is much enlarged. In one species (_M. hellerii_), besides,
the lower caudal rays of the mature male are prolonged into a long,
sword-shaped, generally black and yellow appendage.

Two other genera belong to this group: _Platypoecilus_ and _Girardinus_.


                     SEVENTH FAMILY--HETEROPYGII.

_Head naked; body covered with very small scales; barbels none.
Margin of the upper jaw formed, by the intermaxillaries. Villiform
teeth in the jaws and on the palate. Adipose fin none. Dorsal fin
belonging to the caudal portion of the vertebral column, opposite to
the anal. Ventral fins rudimentary or absent. Vent situated before the
pectorals. Stomach coecal; pyloric appendages present. Pseudobranchiæ
none; air-bladder deeply notched anteriorly._

To this small family, which is closely allied to the Cyprinodonts and
Umbridæ, belongs the famous Blind Fish of the Mammoth Cave in Kentucky,
_Amblyopsis spelæus_. It is destitute of external eyes, and the
body is colourless; although the eyes, with the optic nerve, are quite
rudimentary, the optic lobes are as much developed as in fishes with
perfect eyes. The loss of vision is compensated by the acuteness of
its sense of hearing, as well as by a great number of tactile papillæ,
arranged on transverse ridges on the head, and provided with nervous
filaments coming from the fifth pair. The ovary is single, and the
fish is viviparous, like the Cyprinodonts. It seems to occur in all
the subterranean rivers that flow through the great limestone region
underlying the carboniferous rocks in the central portion of the United
States. As in _Cyprinodon_, so in this genus, specimens occur
without ventral fins; they have been called _Typhlichthys_. The
largest size to which _Amblyopsis_ grows is five inches.

_Chologaster_ is closely allied, but provided with small external
eyes; its body is coloured, but it is destitute of ventrals. It was
found once in a rice field in South Carolina.

   [See Tellkampf, Müll. Arch. 1844, p. 381; Packard and Putnam,
   “The Mammoth Cave and its Inhabitants.” Salem. 1872. 8^o.]


                        EIGHTH FAMILY--UMBRIDÆ.

_Head and body covered with scales; barbels none. Margin of the upper
jaw formed by the intermaxillaries mesially, and by the maxillaries
laterally. Adipose fin none; the dorsal fin belongs partly to the
abdominal portion of the vertebral column. Stomach siphonal; pyloric
appendages none; pseudobranchiæ glandular, hidden; air-bladder
simple._

Two small species only are known: _Umbra krameri_ from Austria and
Hungary, and _Umbra limi_, locally distributed in the United States;
called “Hunds-fish” in Germany, “Dog-fish” or “Mud-fish” in America.


                     NINTH FAMILY--SCOMBRESOCIDÆ.

_Body covered with scales; a series of keeled scales along each side
of the belly. Margin of the upper jaw formed by the intermaxillaries
mesially, and by the maxillaries laterally. Lower pharyngeals united
into a single bone. Dorsal fin opposite the anal, belonging to the
caudal portion of the vertebral column. Adipose fin none. Air-bladder
generally present, simple, sometimes cellular, without pneumatic
duct. Pseudobranchiæ hidden, glandular. Stomach not distinct from the
intestine, which is quite straight, without appendages._

The fishes of this family are chiefly marine, some living in the open
ocean, whilst others have become acclimatised in fresh water; many of
the latter are viviparous, all the marine forms being oviparous. They
are found in all the temperate and tropical zones. Carnivorous.

This family is represented in the strata of Monte Bolca by rare remains
of a fish named _Holosteus_, allied to _Belone_ or _Scombresox_, and
by a species of _Belone_ in the miocene of Licata.

   BELONE.--Both jaws are prolonged into a long slender beak. All
   the dorsal and anal rays connected by membrane.

The long upper jaw of the “Gar-pike” is formed by the intermaxillaries,
which are united by a longitudinal suture. Both jaws are beset with
asperities, and with a series of longer, conical-pointed, widely-set
teeth. Skimming along the surface of the water, the Gar-pike seize
with these long jaws small fish as a bird would seize them with its
beak; but their gullet is narrow, so that they can swallow small fish
only. They swim with an undulating motion of the body; although they
are in constant activity, their progress through the water is much
slower than that of the Mackerels, the shoals of which sometimes
appear simultaneously with them on our coasts. Young specimens are
frequently met in the open ocean; when very young their jaws are not
prolonged, and during growth the lower jaw is much in advance of the
upper, so that these young fishes resemble a _Hemirhamphus_. About
fifty species are known from tropical and temperate seas, _Belone
belone_ being a common fish on the British coast. Its bones, like
those of all its congeners, are green; and therefore the fish, although
good eating, is disliked by many persons. Some species attain a length
of five feet.

   SCOMBRESOX.--Both jaws are prolonged into a long slender beak. A
   number of detached finlets behind the dorsal and anal fins.

The “Saury” or “Skipper” resemble the Gar-pike, but the teeth in the
jaws are minute; they seem to feed chiefly on soft pelagic animals. In
their habits they are still more pelagic; and the young, in which the
beak is still undeveloped, are met with everywhere in the open ocean,
in the Atlantic as well as in the Pacific. The European species,
_Sc. saurus_, is not rare on the British coast; four other species
have been described, closely allied to _Sc. saurus_.

   HEMIRHAMPHUS.--The lower jaw only is prolonged into a long
   slender beak.

In the young both jaws are short; the upper is never prolonged, the
intermaxillaries forming a triangular, more or less convex, plate.
The “Half-beaks” are common between and near the tropics; some forty
species are known, none of which attain to the same length as the
Gar-pike, scarcely ever exceeding a length of two feet. Some of the
tropical species live in fresh water only; they are of small size and
viviparous.

   ARRHAMPHUS.--Mouth formed as in _Hemirhamphus_, except that the
   lower jaw is not produced into a beak. Pectoral fins of moderate
   length.

One species (_A. sclerolepis_) from the coast of Queensland (not
New Zealand); it may be regarded as a _Hemirhamphus_, with retarded
development of the lower jaw.

   EXOCOETUS.--Jaws short, intermaxillaries and maxillaries
   separate. Teeth minute, rudimental, and sometimes absent. Body
   moderately oblong, covered with rather large scales. Pectorals
   very long, an organ of flying.

  [Illustration: Fig. 281.--Flying Fish; Exocoetus callopterus.]

Forty-four different kinds of “Flying-fishes” are known from tropical
and sub-tropical seas; some have a very wide range, whilst others seem
to remain within one particular part of the ocean; thus, the species
figured, _E. callopterus_, has been hitherto found on the Pacific
side of the isthmus of Panama only. Their usual length is about 10 or
12 inches, but specimens of 18 inches have been caught. They always
live in shoals, and their numbers at certain times and localities are
immense; thus, at Barbadoes many boats engage in their capture, as
they are excellent eating. The pectorals are in the various species of
unequal length; in some they extend to the anal fin only; in others
(and these are the best fliers) to the caudal. A few have curious,
barbel-like appendages at the lower jaw, which may disappear with age
or be persistent throughout life. The literature on the subject of
Flying-fishes is very extensive, and great diversity of opinion exists
among observers as regards the mode and power of their flight; but
the most reliable agree that the fishes do not leave the water for
the purpose of catching insects (!), and that they are unable to move
their fins in the manner of a bat or bird, or to change voluntarily the
direction of their flight, or to fly beyond a very limited distance.
The most recent enquiries are those of K. Möbius (“Die Bewegungen
der Fliegenden Fische durch die Luft,” Leip. 1878, 8vo), the chief
results of which may be summed up thus: Flying-fish are more frequently
observed in rough weather and in a disturbed sea than during calm; they
dart out of the water when pursued by their enemies, or frightened
by an approaching vessel, but frequently also without any apparent
cause, as is also observed in many other fishes; and they rise without
regard to the direction of the wind or waves. The fins are kept quietly
distended, without any motion, except an occasional vibration caused
by the air whenever the surface of the wing is parallel with the
current of the wind. Their flight is rapid, but gradually decreasing
in velocity, greatly exceeding that of a ship going 10 miles an hour,
and a distance of 500 feet. Generally, it is longer when the fishes
fly against than with or at an angle to the wind. Any vertical or
horizontal deviation from a straight line is not caused at the will of
the fish, but by currents of the air; thus they retain a horizontally
straight course when flying with or against the wind, but are carried
towards the right or left whenever the direction of the wind is at an
angle with that of their flight. However, it sometimes happens that
the fish during its flight immerses its caudal fin in the water, and
by a stroke of its tail turns towards the right or left. In a calm the
line of their flight is always also vertically straight, or rather
parabolic, like the course of a projectile, but it may become undulated
in a rough sea, when they are flying against the course of the waves;
they then frequently overtop each wave, being carried over it by the
pressure of the disturbed air. Flying-fishes often fall on board of
vessels, but this never happens during a calm, or from the lee side,
but during a breeze only, and from the weather side. In daytime they
avoid a ship, flying away from it; but during the night, when they
are unable to see, they frequently fly against the weather-board,
where they are caught by the current of air, and carried upwards to a
height of 20 feet above the surface of the water, while, under ordinary
circumstances, they keep close to it. All these observations point
clearly to the fact that any deflection from a straight course is due
to external circumstances, and not to voluntary action on the part of
the fish.


                        TENTH FAMILY--ESOCIDÆ.

_Body covered with scales; barbels none. Margin of the upper jaw
formed by the intermaxillaries mesially, and by the maxillaries
laterally. Adipose fin none; the dorsal fin belongs to the caudal
portion of the vertebral column. Stomach without blind sac; pyloric
appendages none. Pseudobranchiæ glandular, hidden; air-bladder simple;
gill-opening very wide._

This family includes one genus only, _Esox_, the “Pikes,” inhabitants
of the fresh waters of the temperate parts of Europe, Asia, and
America. The European species, _E. lucius_, inhabits all three
continents, but the North American waters harbour five, or perhaps
more, other species, of which the “Muskellunge,” or “Maskinonge” (_E.
estor_) of the Great Lakes attains to the same large size as the common
Pike. The other species are generally called “Pickerell” in the United
States.

  [Illustration: Fig. 282.--The Pike. (Esox lucius.)]

Fossil Pike, belonging to the existing genus, have been found in the
freshwater-chalk of Oeningen, and in the diluvial marl of Silesia.
Remains of the common Pike occur in abundance in quaternary deposits.


                      ELEVENTH FAMILY--GALAXIIDÆ.

_Body naked, barbels none. Margin of the upper jaw chiefly formed
by the intermaxillaries, which are short, and continued by a thick
lip, behind which are the maxillaries. Belly rounded; adipose fin
none; dorsal opposite to anal. Pyloric appendages in small number.
Air-bladder large, simple; pseudobranchiæ none. The ova fall into the
cavity of the abdomen before exclusion._

Small freshwater fishes of the southern hemisphere, belonging to two
genera, _Galaxias_ and _Neochanna_. Of the former genus five species
are found in New Zealand, where this type is most developed, three in
New South Wales, two in Tasmania, and four in the southern extremity
of South America. Their native name in New Zealand is “Kokopu,” and
they were dignified with the name of “Trout” by the settlers before the
introduction of true Salmonidæ. They rarely exceed a length of eight
inches. _Neochanna_ is a degraded form of _Galaxias_, from which it
differs by the absence of ventral fins. This fish has hitherto been
found only in burrows, which it excavates in clay or consolidated mud,
at a distance from water.

  [Illustration: Fig. 283.--Galaxias truttaceus, from Tasmania.]


                      TWELFTH FAMILY--MORMYRIDÆ.

_Body and tail scaly; head scaleless; barbels none. The margin of
the upper jaw is formed in the middle by the intermaxillaries, which
coalesce into a single bone, and laterally by the maxillaries. Sub-
and inter-operculum present, the latter very small. On each side of
the single parietal bone a cavity leading into the interior of the
skull, and covered with a thin bony lamella. All the fins are well
developed, in_ Mormyrus; _or caudal, anal, and ventral fins are
absent, in_ Gymnarchus. _No adipose fin. Pseudobranchiæ none;
gill-openings reduced to a short slit. Air-bladder simple. Two coeca
pylorica behind the stomach._

This family is characteristic of the freshwater fauna of tropical
Africa. Of _Mormyrus_ (including _Hyperopisus_ and _Mormyrops_),
fifty-one species are known, of which eleven occur in the Nile. Some
attain a length of three or four feet, others remain small. Their flesh
is said to have an excellent flavour. The species figured (and probably
other allied species) was an object of veneration to the ancient
Egyptians, and, therefore, frequently occurs in their emblematic
inscriptions. They abstained from eating it because it was one of three
different kinds of fishes accused of having devoured a member of the
body of Osiris, which, therefore, Isis was unable to recover when she
collected the rest of the scattered members of her husband.

  [Illustration: Fig. 284.--Mormyrus oxyrhynchus.]

The _Mormyri_ possess a singular organ on each side of the tail,
without electric functions, but evidently representing a transitional
condition from muscular substance to an electric organ. It is an oblong
capsule divided into numerous compartments by vertical transverse
septa, and containing a gelatinous substance. The _Mormyri_ differ
much with regard to the extent of the dorsal and anal fins, the former
sometimes occupying the greater portion of the length of the back,
sometimes being much shorter and limited to the tail. In some the snout
is short and obtuse, in others long and decurved, with or without
appendage.

Of _Gymnarchus_ one species only is known, _G. niloticus_, which occurs
in the Nile and West African rivers, and attains a length of six
feet. The form of its body is eel-like, and each jaw is armed with a
series of incisor-like teeth. Like _Mormyrus_, _Gymnarchus_ possesses
a pseudo-electric organ, thickest on the tail, tapering in front,
and extending nearly to the head. It consists of four membranaceous
tubes intimately connected with the surrounding muscles, and
containing prismatic bodies arranged in the manner of a paternoster.
The air-bladder of Gymnarchus is cellular, very extensible, and
communicates with the dorsal side of the œsophagus by a duct possessing
a sphincter.

   [See _Erdl_, Münchner Gelehrte Anzeigen, 1846, xxiii., and
   _Hyrtl_, Denkschr. Akad. Wiss. Wien. 1856. xii.]


                  THIRTEENTH FAMILY--STERNOPTYCHIDÆ.

_Body naked, or with very thin deciduous scales; barbels none. Margin
of the upper jaw formed by the maxillary and intermaxillary, both
of which are toothed; opercular apparatus not completely developed.
Gill-opening very wide; pseudobranchiæ present or absent; air-bladder
simple, if present. Adipose fin present, but generally rudimentary.
Series of phosphorescent bodies along the lower parts. The eggs are
enclosed in the sacs of the ovarium, and excluded by oviducts._

Pelagic and Deep-sea fishes of small size.

   STERNOPTYX.--Trunk much elevated and compressed, with the trunk
   of the tail very short. Body covered with a silvery pigment,
   without regular scales; series of phosphorescent spots run along
   the lower side of the head, body, and tail. Cleft of the mouth
   wide, vertical, with the lower jaw prominent. Jaws armed with
   small teeth. Eyes rather large, and although lateral, directed
   upwards and placed close together. Ventral fins very small. A
   series of imbricate scutes runs along the abdomen, forming a
   kind of serrature. The dorsal fin is short, and occupies about
   the middle of the length of the fish; it is preceded by the
   first commencement of the formation of a spinous dorsal, several
   neural spines being prolonged beyond the dorsal muscle forming a
   triangular osseous plate. Adipose fin rudimentary; anal short;
   caudal forked.

These small fishes are now and then picked up in the Mediterranean
and Atlantic. According to the dredging-records of the “Challenger,”
they and the allied genera _Argyropelecus_ and _Polyipnus_ would
descend to depths of respectively 1100 and 2500 fathoms; but the form
of their body and their whole organisation render this statement very
improbable; they most likely live at a small depth during the daytime,
coming to the surface at night, like many _Scopelus_.

_Coccia_ and _Maurolicus_ are two other genera allied to the preceding.

  [Illustration: Fig. 285.--Chauliodus sloanii.]

   CHAULIODUS.--Body elongate, compressed, covered with exceedingly
   thin and deciduous scales; series of luminous (phosphorescent)
   spots run along the lower side of the head, body, and tail.
   Head much compressed and elevated, with the bones thin, but
   ossified, and with the opercular portion very narrow, the
   interoperculum being rudimentary. Cleft of the mouth exceedingly
   wide, the intermaxillary forming one half of the upper jaw.
   Each intermaxillary with four long canine teeth; edge of the
   maxillary finely denticulated; mandible with pointed, widely
   set teeth, the anterior of which are exceedingly long; none of
   the large teeth are received within the mouth. Palatine with a
   single series of small pointed teeth; no teeth on the tongue.
   Eye of moderate size. Pectoral and ventral fins well developed.
   Dorsal fin anteriorly on the trunk, before the ventrals; adipose
   fin small, sometimes fimbriated; anal short, rather close to
   the caudal, which is forked. Gill-opening very wide, the outer
   branchial arch extending forward to behind the symphysis of the
   lower jaw; it has no gill-rakers. Branchiostegals numerous.

This genus, of which one species only (_Ch. sloanii_) is known, is
generally distributed over the great depths of the oceans, and does not
appear to be scarce; it attains to a length of 12 inches, and must be
one of the most formidable fishes of prey of the deep-sea.

Allied genera are _Gonostoma_, _Photichthys_, and _Diplophos_, all of
which have the teeth of much smaller size.


                    FOURTEENTH FAMILY--STOMIATIDÆ.

_Skin naked, or with exceedingly delicate scales; a hyoid barbel.
Margin of the upper jaw formed by the intermaxillary and maxillary
which are both toothed; opercular apparatus but little developed.
Gill-opening very wide; pseudobranchiæ none. The eggs are enclosed in
the sacs of the ovarium, and excluded by oviducts._

Deep-sea fishes, descending to the greatest depths, characterised by
their barbel and their formidable dentition.

  [Illustration: Fig. 286.--_Astronesthes niger._ The white
  spots in front of the eye are phosphorescent organs.]

Some have two dorsal fins, the posterior of which is adipose; they
belong to the genus _Astronesthes_, are the smallest of the family, and
frequently met with in the Atlantic.

The others--viz. _Stomias_, _Echiostoma_, _Malacosteus_, and
_Bathyophis_, lack the adipose fin, the rayed dorsal being opposite to
the anal. Of these the one longest known is

   STOMIAS.--Body elongate, compressed, covered with exceedingly
   fine and deciduous scales, which are scarcely imbricate, lying
   in subhexagonal impressions; vent situated at no great distance
   from the caudal fin. Head compressed, with the snout very short,
   and with the cleft of the mouth very wide. Teeth pointed,
   unequal in size, those of the intermaxillaries and of the
   mandible being the longest; maxillary finely denticulated; vomer
   with a pair of fangs; palatine bones and tongue with smaller
   pointed teeth. Eye of moderate size. Opercular portion of the
   head narrow. A fleshy barbel in the centre of the hyoid region.
   Dorsal opposite the anal, close to the caudal; pectoral and
   ventral fins feeble, the latter inserted behind the middle of
   the length of the body. Series of phosphorescent dots run along
   the lower side of the head, body, and tail. Gill-opening very
   wide. Pyloric appendages none.

Three species are known; beside specimens which were found floating on
the surface, others have been dredged from depths varying between 450
and 1800 fathoms.


                     FIFTEENTH FAMILY--SALMONIDÆ.

_Body generally covered with scales; head naked; barbels none. Margin
of the upper jaw formed by the intermaxillaries mesially, and by the
maxillaries laterally. Belly rounded. A small adipose fin behind
the dorsal. Pyloric appendages generally numerous, rarely absent.
Air-bladder large, simple; pseudobranchiæ present. The ova fall into
the cavity of the abdomen before exclusion._

Inhabitants of the sea and freshwater; the majority of the marine
genera are deep-sea forms. The freshwater forms are peculiar to the
temperate and arctic zones of the Northern Hemisphere, one occurring
in New Zealand; many freshwater species periodically or occasionally
descending to the sea. One of the most valuable families of the class
of fishes. No fossils of the freshwater forms are known; but of the
marine genera, _Osmerus_ occurs in the greensand of Ibbenbusen,
and in the schists of Glaris and Licata; a species of _Mallotus_,
indistinguishable from the living _M. villosus_, occurs abundantly in
nodules of clay of unknown geological age in Greenland. Other genera,
as _Osmeroides_, _Acrognathus_, and _Aulolepis_, from the chalk of
Lewes, belong to the same fauna as species of Beryx, and were probably
deep-sea Salmonoids.

   SALMO.--Body covered with small scales. Cleft of the mouth wide,
   the maxillary extending to below or beyond the eye. Dentition
   well developed; conical teeth in the jaw bones, on the vomer
   and palatines, and on the tongue, none on the pterygoid bones.
   Anal short, with less than fourteen rays. Pyloric appendages
   numerous; ova large. Young specimens with dark cross-bands
   (Parr-marks).

We know of no other group of fishes which offers so many difficulties
to the ichthyologist with regard to the distinction of the species
as well as to certain points in their life-history, as this genus,
although this may be partly due to the unusual attention which has been
given to their study, and which has revealed an almost greater amount
of unexplained facts than of satisfactory solutions of the questions
raised. The almost infinite variations of these fishes are dependent
on age, sex and sexual development, food, and the properties of the
water. Some of the species interbreed, and the hybrids mix again with
one of the parent species, thus producing an offspring more or less
similar to the pure breed. The _coloration_ is, first of all, subject
to variation; and consequently this character but rarely assists in
distinguishing a species, there being not one which would show in all
stages of development the same kind of coloration. The young of all the
species are _barred_; and this is so constantly the case that it may
be used as a generic or even as a family character, not being peculiar
to _Salmo_ alone, but also to _Thymallus_ and probably to _Coregonus_.
The number of bars is not quite constant, but the migratory Trout
have two (and even three) more than the River-Trout. In some waters
River-trout remain small, and frequently retain the Parr-marks all
their lifetime; at certain seasons a new coat of scales overlays the
Parr-marks, rendering them invisible for a time; but they reappear
in time, or are distinct as soon as the scales are removed. When the
Salmones have passed this “Parr” state, the coloration becomes much
diversified. The males, especially during and immediately after the
spawning time, are more intensely coloured and variegated than the
females; specimens which have not attained to maturity retaining a
brighter silvery colour, and being more similar to the female fish.
Food appears to have less influence on the coloration of the outer
parts than on that of the flesh; thus the more variegated specimens are
frequently out of condition, whilst well-fed individuals with pinkish
flesh are of a more uniform though bright coloration. Chemistry has
not supplied us yet with an analysis of the substance which gives the
pink colour to the flesh of many Salmonoids; but there is little doubt
that it is identical with, and produced by, the red pigments of many
salt- and freshwater Crustaceans, which form a favourite food of these
fishes. The water has a marked influence on the colours; Trout with
intense ocellated spots are generally found in clear rapid rivers, and
in small open Alpine pools; in the large lakes with pebbly bottom the
fish are bright silvery, and the ocellated spots are mixed with or
replaced by X-shaped black spots; in pools or parts of lakes with muddy
or peaty bottom, the trout are of a darker colour generally, and when
enclosed in caves or holes, they may assume an almost uniform blackish
coloration.

The change of scales (that is, the rapid reproduction of the worn
part of the scales) coincides in the migratory species with their
sojourn in the sea. The renovated scales give them a bright silvery
appearance, most of the spots disappearing or being overlaid and hidden
by the silvery scales. Now, some of the species, like _S. fario_,
inhabit all the different waters indicated, even brackish water, and,
in consequence, we find a great variation of colour in one and the
same species; others are more restricted in their habitat, like _S.
salar_, _S. ferox_, etc., and, therefore, their coloration may be more
precisely defined.

With regard to _size_ the various species do not present an equal
amount of variation. Size appears to depend on the abundance of food
and the extent of the water. Thus, the Salmon and the different kinds
of great Lake-trout do not appear to vary considerably in size, because
they find the same conditions in all the localities inhabited by them.
A widely spread species, however, like _S. fario_, when it inhabits
a small mountain pool with scanty food, may never exceed a weight
of eight ounces, whilst in a large lake or river, where it finds an
abundance and variety of food, it attains to a weight of fourteen
or sixteen pounds. Such large River-trout are frequently named and
described as Salmon-trout, Bull-trout, etc. Further, in Salmones, as
in the majority of fishes and tailed Batrachians, there is an innate
diversity of growth in individuals hatched from the same spawn. Some
grow rapidly and normally, others more slowly, and some remain dwarfed
and stationary at a certain stage of development.

The _proportions of the various parts of the body_ to one another vary
exceedingly in one and the same species. Beside the usual changes from
the young to the sexually mature form observed in all fishes, the snout
undergoes an extraordinary amount of alteration of shape. In the mature
male the intermaxillaries and the mandible are produced in various
degrees, and the latter is frequently more or less bent upwards. Hence
the males have the snout much more pointed and produced, and the entire
head longer, than the females; with the intermaxillary bone the teeth,
with which it is armed, are also enlarged, sometimes to four times the
size of those of the females. And if this development of the front
part of the head happens to be going on while the individual is able
to obtain only a scanty supply of food, the usual proportions of the
head and trunk are so altered that the species is very difficult to
recognise. Barren male fish approach the females in the proportions of
the head and body, but hybrid fishes do not differ in this respect from
their parents. The abundance or scarcity of food, and the disposition
or indisposition of the Salmonoids to feed, are other causes affecting
the growth or fulness of the various parts of the body. In well-fed
fishes the head is proportionally not only smaller but also shorter,
and _vice versa_.

The _fins_ vary to a certain degree. The variation in the number of
the rays is inconsiderable and of no value for specific distinction.
The caudal fin undergoes considerable changes of form with age,
and dependency upon the sexual development. Young specimens of all
species have this fin more or less deeply excised, so that the young
of a species which has the caudal emarginate throughout life, is
distinguished by a deeper incision of the fin, from the young of a
species which has it truncate in the adult state. As the individuals of
a species do not all attain to maturity at the same age and at the same
size, and as mature individuals generally have the caudal less deeply
excised than immature ones of the same age and size, it is evident that
the variations in the form of the caudal are considerable and numerous,
and that it is a very misleading character if due regard be not paid to
the age and sexual development of the fish. Further, species inhabiting
rapid streams as well as still waters show considerable variations in
the form and length of all the fins; those individuals which live in
rapid streams, being in almost constant motion and wearing off the
delicate extremities of the fins, have the fin-rays comparatively
shorter and stouter, and the fins of a more rounded form, particularly
at the corners, than individuals inhabiting ponds or lakes. Moreover,
one and the same individual may pass a part of its life in a lake, and
enter a river at certain periods, thus changing the form of its fins
almost periodically.

Finally, to complete our enumeration of these variable characters, we
must mention that in old males, during and after the spawning-season,
the _skin_ on the back becomes thickened and spongy, so that the scales
are quite invisible, being imbedded in the skin.

       *       *       *       *       *

After this cursory review of variable characters we pass on to those
which are more constant, not subject to ready modification by external
circumstances; and which, therefore, ought to be noticed in every
description of a species of Salmo.

1. _The form of the præoperculum of the adult fish._ The præoperculum
is composed of a vertical (posterior) and horizontal (lower) part
(limb), both meeting at a more or less rounded angle. The development
of the lower limb is a very constant character; in some species (as
in the Salmon) it is long, in others (_S. ferox_, _S. brachypoma_)
exceedingly short. The adjoining woodcuts will readily show this
difference.

  [Illustration: Fig. 287.--Præoperculum of A. Salmo salar; B.
  Salmo brachypoma.]

In young specimens of all Salmonoids the præoperculum has a very short
lower limb; but whilst in some species it lengthens with age, its
development in a horizontal direction is arrested in others.

2. _The width and strength of the maxillary of the adult fish._--To
show this character in two distinct species, we have given woodcuts
of the maxillaries of females (12 inches long) of _S. fario_ and _S.
levenensis_ of the same size.

  [Illustration: Fig. 288.--Maxillary of A. Salmo fario; B. Salmo
  levenensis.]

In young specimens of all Salmonoids the maxillary is comparatively
shorter and broader, somewhat resembling that of _Coregonus_; yet this
bone offers a valuable character for the determination of the young
of some species; for instance, in a young _S. cambricus_ it extends
scarcely to below the centre of the eye, whilst in _S. fario_ of the
same size it reaches to, or even beyond, this point.

  [Illustration: Fig. 289.--Vomerine teeth of Salmo salar (Salmon).
  A. Side view. B. Lower view.]

3. _The size of the teeth, those of the intermaxillaries excepted._

4. _The arrangement, and the permanence or deciduousness of the
vomerine teeth._--In some species the vomer is normally armed with
a double or single series throughout life, although, of course, some
of the teeth are frequently accidentally lost; in others, these teeth
disappear gradually with age, the hinder ones first, so that finally
the anterior only remain. In order to ascertain the arrangement of
the teeth, it is necessary to remove the gengiva. Frequently the
teeth stand in a distinctly double or single series, or they are
placed alternately; but frequent irregularities occur which render
the character vague, or even unsafe, so that some zoologists have
rejected it entirely as unreliable. However, when a greater number of
individuals really belonging to the same species are examined, a pretty
safe conclusion may be arrived at as regards the arrangement of the
teeth.

  [Illustration: Fig. 290.--Vomerine teeth of Salmo fario, lower
  view.]

  [Illustration: Fig. 291.--Vomerine teeth of a Charr, side view.]

5. _The form of the caudal fin_ in specimens of a given size, age,
and sexual development.

6. _A great development of the pectoral fins_, when constant in
individuals from the same locality.

7. _The size of the scales_, as indicated by the number of transverse
rows above the lateral line: one of the most constant characters.

8. _The number of vertebræ._--Considering the great number of
vertebræ in Salmonoids the constancy of this character is truly
surprising. An excess or a diminution of the normal number by two, is
of rare occurrence, and generally to be explained by the fact that
one vertebra has been abnormally divided into two, two such vertebræ
being considerably smaller than the others; or, on the other hand,
that two have merged into one centrum, which is then unusually large,
and provided with two neural spines. We have seen one case only, in
which three vertebræ were united. The number of vertebræ can be easily
ascertained in specimens destined for preservation in spirits, by an
incision made along one side of the fish, a little above the lateral
line.

9. _The number of pyloric appendages._--There can be no doubt that
this character may materially assist in fixing a species. We shall see
that in some species it varies from 30 to 50; but in others, as in the
Salmon and Charr, it has been found very constant (see Fig. 56, p.
131). If unexpected variations occur, their cause may be found in a
partial confluence of the cæca, as we have observed that specimens of
_S. levenensis_ (a species normally with from 70 to 90 cæca), had
those appendages of unusual width when the normal number was diminished.

       *       *       *       *       *

We have mentioned above that many points in the _life-history_ of
the Salmonoids still remain very obscure:--

1. Johnson, a correspondent of Willughby (“Hist. Pisc.,” p. 194), had
already expressed his belief that the different Salmonoids interbreed;
and this view has since been shared by many who have observed these
fishes in nature. Hybrids between the Sewin (_S. cambricus_) and
the River Trout (_S. fario_) were numerous in the Rhymney and other
rivers of South Wales, before Salmonoids were almost exterminated by
the pollutions allowed to pass into those streams, and so variable
in their characters that the passage from one species to the other
could be demonstrated in an almost unbroken series, which might
induce some naturalists to regard both species as identical. Abundant
evidence of a similar character has accumulated, showing the frequent
occurrence of hybrids between _S. fario_ and _S. trutta_; hybrids
between _S. fario_ and species of Charr have been abundantly bred by
continental pisciculturists. In some rivers the conditions appear to
be more favourable to hybridism than in others, in which hybrids are
of comparatively rare occurrence. Hybrids between the Salmon and some
other species are very scarce everywhere. The hybrids are sexually as
much developed as the pure breed, but nothing whatever is known of
their further propagation and progeny.

2. Siebold has shown that some individuals of every species are not
sexually developed, and that such individuals differ also externally
from those normally developed. However, he appears to have gone too
far when he stated that this state of sterility extends over the whole
existence of such individuals, and that, therefore, the external
peculiarities also remain permanent throughout life. According to
Widegren this sterility is merely a temporary immaturity, and a part of
the individuals arrive at a full sexual development at a later or much
later period than others. To this we may add that many Salmonoids cease
to propagate their species after a certain age, and that all so called
overgrown individuals (that is, specimens much exceeding the usual size
of the species) are barren. Externally they retain the normal specific
characters.

The Salmon offers a most remarkable instance of irregularity as
regards the age at which the individuals arrive at maturity. Shaw
has demonstrated, in the most conclusive manner, that those small
Salmonoids, which are generally called Parr, are the offspring of the
Salmon, and that many males, from 7 to 8 inches long, have their sexual
organs fully developed, and that their milt has all the impregnating
properties of the seminal fluid of a much older and larger fish. That
this Parr is not a distinct species--as has been again maintained by
Couch--is further proved by the circumstance that these sexually mature
Parr are absolutely identical in their zoological characters with the
immature Parr, which are undoubtedly young Salmon, and that no Parr
has ever been found with mature ova. But whether these Parr produce
normal Salmon, impregnating the ova of female salmon, or mingle with
the River-trout, or whether they continue to grow and propagate their
species as fully developed Salmon, are questions which remain to be
answered. We may only add that, as far as we know, barren old Salmon
are extremely scarce.

3. The question whether any of the migratory species can be retained
by artificial means in fresh water, and finally accommodate themselves
to a permanent sojourn therein, must be negatived for the present.
Several instances of successful experiments made for this purpose
have been brought forward; but all these accounts are open to serious
doubts, inasmuch as they do not afford us sufficient proof that
the young fish introduced into ponds were really young migratory
Salmonoids, or that the full-grown specimens were identical with those
introduced, and not hybrids or non-migratory Trout of a somewhat
altered appearance in consequence of the change of their locality.
We have seen the experiment tried at two places in South Wales, and
in both cases the Salmon and the pure Sewin died when not allowed to
return to the sea. On the other hand, hybrid fishes from the Sewin and
the Trout survived the experiment, and continued to grow in a pond
perfectly shut up from communication with the sea. In that locality
neither those hybrids nor the trout spawn.

4. Although the majority of the mature individuals of a migratory
species ascend a river at a certain fixed time before the commencement
of spawning, others enter the freshwater at a much earlier period,
either singly or in small troops; and many appear to return to the sea
before they reascend at the time of the regular immigration. It is
not improbable that one and the same individual may change the salt-
or freshwater several times in the year. However, this is the case in
certain rivers only, for instance, in those falling into the Moray
Firth; in others one immigration only is known to occur. The cause of
the irregular ascents previous to the autumnal ascents is unknown. A
part, at least, of the hybrid fishes retain the migratory instinct; but
it is not known whether sterile individuals accompany the others in
their migrations.

5. It is said that the migratory species invariably return to the river
in which they are bred. Experiments have shown that this is normally
the case; but a small proportion appear to stray so far away from
their native place as to be unable to find their way back. Almost every
year Salmon and Sea-trout in the Grilse-state make their appearance at
the mouth of the Thames (where the migrating Salmonoids have become
extinct for many years), ready to reascend and to restock this river as
soon as its poisoned water shall be sufficiently purified to allow them
a passage.

6. There has been much dispute about the time required for the growth
of Salmonoids. The numerous and apparently contradictory observations
tend to show that there is a great amount of variation even among
individuals of the same origin living under the same circumstances,
some of them growing much more quickly than others, and being ready to
descend to the sea twelve months before their brethren. The cause of
this irregularity is not explained. On the other hand, when we consider
the fibrous condition of the Salmonoid skeleton, which is much less
solid, and more wanting in calcareous substance, than that of the
majority of Teleosteous fishes, we shall be quite prepared to adopt the
truth of the observation that the young Salmonoids return to the fresh
water, after a few months sojourn in the sea, and after having feasted
on nourishing Crustaceans, Sand-eels, etc., with their former weight in
ounces increased to pounds.

7. Liability to variation in form indicates that an animal can adapt
itself to a variety of circumstances; therefore, such species as show
the greatest pliability in this respect, are those which most recommend
themselves for domestication and acclimatisation within certain
climatic limits. Thus, the River-trout or Sea-trout were very proper
subjects for those eminently successful attempts to establish them in
similar latitudes of the Southern Hemisphere, whilst the attempt of
transferring them into the low hill-streams of India ended (as could be
foreseen) in a total failure. Those two species must now be considered
to be fully acclimatised in Tasmania and New Zealand, and with but
little protection may be expected to hold their own in the freshwaters
of those colonies. Whether the acclimatisation of the Salmon will be
in the end equally and permanently successful, remains to be seen.
The true _S. salar_ is not subject to variation, and is very
sensitive to any change of external conditions, and to every kind of
interference with its economy. The fourth species, with which attempts
of acclimatisation in Southern Australia have been made, is a migratory
Salmon from the Sacramento river in California. This experiment is
still in progress, and believed to be promising of success. It will be
a most curious problem to ascertain, how much the original characters
and habits of those species will be affected by their transference to
so distant a part of the globe. At present it would be too hazardous
to offer an opinion on this point, especially as it is a fact that
numerous cross-breeds have been introduced into, and reared in,
Tasmania, which must more or less interfere with the characters of the
pure breeds.

It is apparent, from the foregoing remarks, that the distinction
of the various species of Salmonidæ is a matter of considerable
difficulty, and that there is scope for great diversity of opinion.
At any rate it is only by a close, long-continued study, and constant
comparison of specimens of various ages and from various localities,
that one is enabled to find a guide through the labyrinth of confusing
variations. However, it is a significant fact that the very same
characters by which we are enabled to distinguish European species
occur again, though in an exaggerated form, in American Salmonoids
(which everybody will admit to be of distinct species), and therefore
our faith in them necessarily becomes strengthened. In accordance with
acknowledged principles in zoology, forms which differ from their
congeners by a combination of two or more of constant characters, are
to be distinguished under distinct specific names. Most likely they
have been derived, at a not very remote period, from common ancestors,
but the question of their specific distinctness is no more affected
by this consideration than the question whether _Salmo_ and
_Coregonus_ are distinct genera. Whenever the zoologist observes
two forms distinguished by peculiarities of organisation, such as
cannot be conceived to be the effects of an external or internal cause,
disappearing with the disappearance of that cause, and which forms
have been propagated and are being propagated uniformly through all
the generations within the limits of our observations, and are yet
most probably to be propagated during the existence of mankind, he is
obliged to describe these forms as distinct, and they will commonly be
called species.

The species of the genus _Salmo_ are inhabitants of the temperate
and arctic zones of the Northern Hemisphere; the species are most
abundant in the northern parts of the temperate zone, becoming scarcer
beyond the Arctic circle, and in the warmer parts towards the south.
The southernmost points in which Salmones are found, are, on the
American continent, the rivers falling into the head of the Californian
Gulf, and in the Old World the mountain rivers of the Atlas and Hindu
Kush. The Salmones from those localities are migratory Trout in the New
World, non-migratory and small in the Old. Those species which range
to the highest latitudes (lat. 82°) belong to the division of Charr, a
group which generally are more intolerant of a moderate temperature,
than real Trout. The genus is subdivided into

   _a. Salmones_--Salmon and Trout--with teeth on the body of the
   vomer as well as its head (see Figs. 289 and 290).

   _b. Salvelini_--Charr--with teeth on the head of the vomer only
   (see Fig. 291).

  [Illustration: Fig. 292.--Salmo brachypoma.]

Of the host of species (the majority of which is unfortunately very
insufficiently characterised) we enumerate the following:--[45]


                            _a._ SALMONES.

   1. _S. salar_ (Salmon; Lachs or Salm; Saumon) (Fig. 6, p. 43).
   The Salmon can generally be readily recognised, but there are
   instances in which the identification of specimens is doubtful,
   and in which the following characters (besides others) will be
   of great assistance. The tail is covered with relatively large
   scales, there being constantly eleven, or sometimes twelve in a
   transverse series running from behind the adipose fin forwards
   to the lateral line, whilst there are from thirteen to fifteen
   in the different kinds of Sea-trout and River-trout. The number
   of pyloric appendages (see Fig. 56, p. 131) is great, generally
   between 60 and 70, more rarely falling to 53 or rising to 77.
   The body of the vomer is armed with a single series of small
   teeth, which at an early age are gradually lost from behind
   towards the front, so that half-grown and old individuals have
   only a few (1–4) left. The Salmon inhabits temperate Europe
   southwards to 43° N. lat., and is not found in any of the rivers
   falling into the Mediterranean. In the New World its southern
   boundary is 41° N. lat.

   2. _S. trutta_ (Sea-trout, Salmon-trout).[46]--Especially
   numerous in North Britain.

   3. _S. cambricus_ (Sewin).--Wales, South of England, Ireland,
   Norway, and Denmark.

   4. _S. fario_ (Common River-trout).

   5. _S. macrostigma_ (Algeria).

   6. _S. lemanus_ (Lake of Geneva).

   7. _S. brachypoma._--A migratory species from the rivers Forth,
   Tweed, and Ouse.

   8. _S. gallivensis_ (Galway Sea-trout).

   9. _S. orcadensis._--A non-migratory trout from Lough Stennis,
   in the Orkney Islands.

   10. _S. ferox._--The great Lake-trout of North Britain, Wales,
   and Ireland.

   11. _S. stomachicus_ (the Gillaroo of Ireland).

   12. _S. nigripinnis_ from mountain-pools of Wales.

   13. _S. levenensis_ (Lochleven Trout).

   14. _S. oxi_ from the rivers of the Hindu Kush.

   15. _S. purpuratus_ from the Pacific coast of Asia and North
   America.

   16. _S. macrostoma._--Japan.

   17. _S. namaycush._--The great Lake-trout of North America.


                        _b._ SALVELINI: Charr.

   1. _S. umbla._--The “Ombre chevalier” of the Swiss lakes.

   2. _S. salvelinus._--The “Sælbling” of the Alpine lakes of
   Bavaria and Austria.

   3. _S. alpinus._--The common Northern Charr, growing to a length
   of four feet, and migratory.

   4. _S. killinensis._--The Loch Killin Charr, Inverness-shire.

   5. _S. willughbii._--The Loch Windermere Charr.

   6. _S. perisii._--The “Torgoch” of Wales.

   7. _S. grayi._--The “Freshwater Herring” of Lough Melvin,
   Ireland.

   8. _S. colii._--Charr of Loughs Eske and Dan.

   9. _S. hucho._--The “Huchen” of the Danube, growing to the size
   of the Salmon.

   10. _S. alipes_ from lakes in Boothia Felix and Greenland.

   11. _S. arcturus._--The most northern species from 82° lat.

   12. _S. fontinalis._--The common “Brook-trout” of the United
   States.

   13. _S. oquassa._--A lake species from the State of Maine.

_Oncorhynchus_ differs from _Salmo_ only in the increased number of
anal rays, which are more than fourteen. All the species are migratory,
ascending American and Asiatic rivers flowing into the Pacific. The
Californian Salmon (_O. quinnat?_) belongs to this genus.

Other allied genera are _Brachymystax_ and _Luciotrutta_.

   PLECOGLOSSUS.--Body covered with very small scales. Cleft of the
   mouth wide; maxillary long. Dentition feeble; intermaxillaries
   with a few small, conical, pointed teeth; the teeth of the
   maxillaries and mandibles are broad, truncated, lamellated
   and serrated, movable, seated in a fold of the skin. The
   mandibles terminate each in a small knob, and are not jointed
   at the symphysis. The mucous membrane in the interior of the
   mouth--between the terminal halves of the mandibles--forms a
   peculiar organ, being raised into folds, with a pair of pouches
   in front and a single one behind. Tongue very small, with minute
   teeth, its apical part being toothless; palate apparently
   without teeth.

A small aberrant form of Freshwater-Salmonoids abundantly found in
Japan and the Island of Formosa.

   OSMERUS.--Body covered with scales of moderate size. Cleft of
   the mouth wide; maxillary long, extending to, or nearly to, the
   hind margin of the orbit. Dentition strong; intermaxillary and
   maxillary teeth small, much smaller than those of the mandible.
   Vomer with a transverse series of teeth, several of which are
   large, fang-like; a series of conical teeth along the palatine
   and pterygoid bones. Tongue with very strong fang-like teeth
   anteriorly, and with several longitudinal series of smaller
   ones posteriorly. Pectoral fins moderately developed. Pyloric
   appendages very short, in small number; ova small.

The “Smelt” (_O. eperlanus_) is common on many places of the coasts of
Northern Europe and America. In the sea it grows to a length of eight
inches; but, singularly, it frequently migrates from the sea into
rivers and lakes, where its growth is very much retarded. That this
habit is one of very old date, is evident from the fact that this small
freshwater form occurs, and is fully acclimatised in lakes which have
now no open communication with the sea. And still more singularly, this
same habit, with the same result, has been observed in the Smelt of New
Zealand (_Retropinna richardsonii_). The Smelt is considered a delicacy
in Europe, as well as in America, where the same species occurs. Two
other allied genera, _Hypomesus_ and _Thaleichthys_, are found on the
Pacific coast of North America, the latter being caught in immense
numbers, and known by the name “Eulachon” and “Oulachan;” it is so fat,
that it is equally used as food and as candle.

   MALLOTUS.--Body covered with minute scales, which are
   somewhat larger along the lateral line and along each side
   of the belly; in mature males these scales become elongate,
   lanceolate, densely tiled, with free projecting points, forming
   villous bands. Cleft of the mouth wide; maxillary very thin,
   lamelliform, extending to below the middle of the eye. Lower jaw
   the longer, partly received between the maxillaries. Dentition
   very feeble; the teeth forming single series; only the teeth on
   the tongue are somewhat larger and disposed in an elliptical
   patch. Pectoral fins large, horizontal, with broad base. Pyloric
   appendages very short, in small number; ova small.

The “Capelin” (_M. villosus_) is found on the Arctic coasts of
America and of Kamtschatka. It is caught in immense numbers by the
natives, who consume it fresh, or dry it for use in the winter. Its
length does not exceed nine inches.

   COREGONUS.--Body covered with scales of moderate size. Cleft of
   the mouth small; maxillary broad, short or of moderate length,
   not extending behind the orbit. Teeth, if present, extremely
   minute and deciduous. Dorsal fin of moderate length; caudal
   deeply forked. Ova small.

  [Illustration: Fig. 293.--Coregonus oxyrhynchus.]

  [Illustration: Fig. 294.--Head of Coregonus oxyrhynchus.]

The majority of the species, of which more than forty are known, are
lacustrine species; and comparatively few are subject to periodical
migrations to the sea, like _Salmo_. They are confined to the northern
parts of temperate Europe, Asia, and North America. Their distribution
is local, but sometimes three and more species are found in the same
lake. They abound in every lake and river of the northern parts of
North America, and are known by the name of “White-fish.” They are of
vital importance to some tribes of the native population. The European
_C. oxyrhynchus_ is as much a marine as a freshwater species. In the
British Islands several small species occur, viz. _C. clupeoides_, the
“Gwyniad,” “Schelly,” or “Powen” from the great lakes; _C. vandesius_,
the “Vendace” of Lochmaben; and _C. pollan_, the “Pollan” of the Irish
lakes. The latter is brought in quantities to Belfast market during
the season, that is, at the time when it rises from the depths of
Lough Neagh to deposit its spawn near the shore. Thomson says that in
September 1834 some 17,000 were taken there at three or four draughts
of the net. Some of the species of the continent of Europe and America
attain to a much larger size than the British species, viz. to a length
of two feet.

  [Illustration: Fig. 295.--Coregonus clupeoides.]

   THYMALLUS.--Principally distinguished from _Coregonus_ by its
   long many-rayed dorsal fin.

“Graylings”--five species, inhabiting clear streams of the north of
Europe, Asia, and North America. The best known are the “Poisson bleu”
of the Canadian voyageurs (_Th. signifer_), and the European
Grayling (_T. vulgaris_).

   SALANX.--Body elongate, compressed, naked or covered with
   small, exceedingly fine, deciduous scales. Head elongate and
   much depressed, terminating in a long, flat, pointed snout. Eye
   small. Cleft of the mouth wide; jaws and palatine bones with
   conical teeth, some of the intermaxillaries and mandibles being
   enlarged; no teeth on the vomer; tongue with a single series of
   curved teeth. Dorsal fin placed far behind the ventrals, but in
   front of the anal; anal long; adipose fin small; caudal forked.
   Pseudobranchiæ well developed; air-bladder none. The entire
   alimentary canal straight, without bend; pyloric appendages
   none. Ova small.

This small, transparent, or whitish fish _(S. chinensis_) is well
known at Canton and other places of the coast of China as “White-bait,”
and considered a delicacy. It is evidently a fish which lives at a
considerable depth in the sea, and approaches the coast only at certain
seasons.

Finally, this family is represented in the deep sea by three genera,
_Argentina_, _Microstoma_, and _Bathylagus_, of which the two former
live at moderate depths, and have been known for a long time, whilst
the last was discovered during the “Challenger” expedition in the
Atlantic and Antarctic Oceans at depths of 1950 and 2040 fathoms. As
_Argentina_ is sometimes found in the North Atlantic, and even near the
British coasts, we give its principal characters.

   ARGENTINA.--Scales rather large; cleft of the mouth small;
   intermaxillaries and maxillaries very short, not extending
   to below the orbit. Eye large. Jaws without teeth; an arched
   series of minute teeth across the head of the vomer and on the
   fore part of the palatines; tongue armed with a series of small
   curved teeth on each side. Dorsal fin short, in advance of the
   ventrals; caudal deeply forked. Pseudobranchiæ well developed.
   Pyloric appendages in moderate numbers. Ova small.

Four species are known, of which _A. silus_ and _A. hebridica_ have
been found occasionally on the North British, and, more frequently,
on the Norwegian coast. The other species are from the Mediterranean.
Attaining to a length of 18 inches.


                     SIXTEENTH FAMILY--PERCOPSIDÆ.

_Body covered with ctenoid scales; head naked. Margin of the upper
jaw formed by the intermaxillaries only; opercular apparatus complete.
Barbels none. Gill-openings wide. Adipose fin present._

One genus and species only (_Percopsis guttatus_); interesting as
having the general characters of Salmonoids, but the mouth and scales
of a Percoid. Freshwaters of the northern United States.


                  SEVENTEENTH FAMILY--HAPLOCHITONIDÆ.

_Body naked or scaly (cycloid). Margin of the upper jaw formed
by the intermaxillary; opercular apparatus complete. Barbels none.
Gill-opening wide; pseudobranchiæ. Air-bladder simple. Adipose fin
present. Ovaries laminated; the eggs fall into the cavity of the
abdomen, there being no oviduct. Pyloric appendages none._

  [Illustration: Fig. 296.--Prototroctes oxyrhynchus, New Zealand.]

Freshwater-fishes which represent the Salmonoids in the southern
hemisphere. Two genera only are known. _Haplochiton_ (Fig. 104, p. 250)
abundant in lakes and the streams falling into the Straits of Magelhæn
and in the rivers of Chile and the Falkland Islands. It has the general
appearance of a Trout, but is naked. _Prototroctes_, with the habit of
a _Coregonus_, scaly, and provided with minute teeth; one species (_P.
maræna_) is common in South Australia, the other (_P. oxyrhynchus_) in
New Zealand. The settlers in these colonies call them Grayling; the
Maori name of the second species is “Upokororo.”


                   EIGHTEENTH FAMILY--GONORHYNCHIDÆ.

_Head and body entirely covered with spiny scales; mouth with
barbels. Margin of the upper jaw formed by the intermaxillary, which,
although short, is continued downwards as a thick lip, situated in
front of the maxillary. Adipose fin none; the dorsal fin is opposite to
the ventrals, and short, like the anal. Stomach simple, without blind
sac; pyloric appendages in small number. Pseudobranchiæ; air-bladder
absent. Gill-openings narrow._

  [Illustration: Fig. 297.--Gonorhynchus greyi.]

  [Illustration: Fig. 298.--Scale of Gonorhynchus greyi.]

One genus and species only (_Gonorhynchus greyi_) is known; it is a
semi-pelagic fish, not very rare off the Cape of Good Hope, and in the
Australian and Japanese seas. From 12 to 18 inches long. The colonists
in New Zealand name it “Sand-eel,” as it frequents bays with sandy
bottom. It is eaten.


                    NINETEENTH FAMILY--HYODONTIDÆ.

_Body covered with cycloid scales; head naked; barbels none. Margin
of the upper jaw formed by the intermaxillaries mesially, and by the
maxillaries laterally, the latter being articulated to the end of the
former. Opercular apparatus complete. Adipose fin none; the dorsal
fin belongs to the caudal portion of the vertebral column. Stomach
horseshoe-shaped, without blind sac; intestine short; one pyloric
appendage. Pseudobranchiæ none; air-bladder simple. Gill-openings wide.
The ova fall into the abdominal cavity before exclusion._

One genus and species only (_Hyodon tergisus_) is known, generally
called “Moon-eye.” It is abundant in the western streams and great
lakes of North America. From 12 to 18 inches long.


                    TWENTIETH FAMILY--PANTODONTIDÆ.

_Body covered with large cycloid scales; sides of the head osseous.
Margin of the upper jaw formed by the single intermaxillary mesially,
and by the maxillaries laterally. The dorsal fin belongs to the caudal
portion of the vertebral column, is short, opposite and similar to the
anal. Gill-openings wide; gill-covers consisting of a præoperculum
and operculum only. Branchiostegals numerous. Pseudobranchiæ none;
air-bladder simple. Stomach without coecal sac; one pyloric appendage.
Sexual organs with a duct._

A small freshwater-fish (_Pantodon buchholzi_), singularly alike to a
Cyprinodont, from the west coast of Africa.


                  TWENTY-FIRST FAMILY--OSTEOGLOSSIDÆ.

_Body covered with large hard scales, composed of pieces like
mosaic. Head scaleless; its integuments nearly entirely replaced by
bone; lateral line composed of wide openings of the mucus-duct. Margin
of the upper jaw formed by the intermaxillaries mesially, and by the
maxillaries laterally. The dorsal fin belongs to the caudal portion of
the vertebral column, is opposite and very similar to the anal fin;
both approximate to the rounded caudal (with which they are abnormally
confluent). Gill-openings wide; pseudobranchiæ none; air-bladder simple
or cellular. Stomach without coecal sac; pyloric appendages two._

Large freshwater-fishes of the tropics, whose singular geographical
distribution has been noticed above (p. 223).

   OSTEOGLOSSUM.--Cleft of the mouth very wide, oblique, with the
   lower jaw prominent. A pair of barbels at the lower jaw. Abdomen
   trenchant. Bands of rasp-like teeth on the vomer, palatine and
   pterygoid bones, on the tongue and hyoid. Pectoral fins elongate.

_O. bicirrhosum_ from Brazil and Guyana, _O. formosum_ from Borneo and
Sumatra, _O. leichardti_ from Queensland.

   ARAPAIMA.--Cleft of the mouth wide, with the lower jaw
   prominent; barbels none. Abdomen rounded. Jaws with an outer
   series of small conical teeth; broad bands of rasp-like teeth
   on the vomer, palatines, pterygoids, sphenoid, os linguale, and
   hyoid. Pectoral fins of moderate length.

  [Illustration: Fig. 299.--Arapaima gigas.]

The largest freshwater Teleostean known, exceeding a length of 15 feet
and a weight of 400 pounds. It is common in the large rivers of Brazil
and the Guyanas, and esteemed as an article of food. When salted it is
exported in large quantities from the inland fisheries to the seaports.

   HETEROTIS.--Cleft of the mouth rather small, with the jaws
   subequal; barbels none. A single series of small teeth in the
   jaws; pterygoids and hyoid with a patch of small conical teeth;
   none on the vomer or palatines.

This fish (_H. niloticus_), which is not uncommon in the Upper Nile and
the West African rivers, exhibits several anatomical peculiarities. The
fourth branchial arch supports a spiral accessory organ, the function
of which is still unexplained. The air-bladder is cellular, and the
stomach consists of a membranous and a muscular portion.


                    TWENTY-SECOND FAMILY--CLUPEIDÆ.

_Body covered with scales; head naked; barbels none. Abdomen
frequently compressed into a serrated edge. Margin of the upper jaw
formed by the intermaxillaries mesially, and by the maxillaries
laterally; maxillaries composed of at least three movable pieces.
Opercular apparatus complete. Adipose fin none. Dorsal not elongate;
anal sometimes very long. Stomach with a blind sac; pyloric appendages
numerous. Gill-apparatus much developed, the gill-openings being
generally very wide. Pseudobranchiæ generally present. Air-bladder more
or less simple._

The family of “Herrings” is probably unsurpassed by any other in the
number of individuals, although others comprise a much greater variety
of species. The Herrings are principally coast-fishes, or, at least, do
not go far from the shore; none belong to the deep-sea fauna; scarcely
any have pelagic habits, but many enter or live in fresh waters
communicating with the sea. They are spread over all the temperate
and tropical zones. Fossil remains of Herrings are numerous, but the
pertinence of some of the genera to this family is open to serious
doubts, as the remains are too fragmentary to allow of determining
whether they belong to Salmonoids or Clupeoids. Therefore, Agassiz
comprised both families in one--_Halecidæ_. Many of the remains
belong to recent genera, which are readily recognised, as _Clupea_,
_Engraulis_ and _Chanos_, principally from the schists of Glaris and
Licata, from Monte Bolca and the Lebanon. Others, like _Thrissopater_,
from the Gault at Folkestone, _Leptosomus_, _Opisthopteryx_,
_Spaniodon_, from the chalk and tertiary formations, can be readily
associated with recent genera. But the majority do not show an apparent
affinity to the present fauna. Thus, _Halec_ from the chalk of Bohemia,
_Platinx_ and _Coelogaster_ from Monte Bolca, _Rhinellus_ from Monte
Bolca and Mount Lebanon, _Scombroclupea_, with finlets behind the
anal, from the Lebanon and Comen, and _Crossognathus_ from tertiary
Swiss formations, allied to _Megalops_, _Spathodactylus_ from the same
locality, and _Chirocentrites_ from Mount Lebanon, etc. Finally, a
genus recently discovered in tertiary formations of Northern Italy,
_Hemitrichas_, has been classed with the Clupeoids, from which,
however, it differs by having two short dorsal fins, so that it must
be considered, without doubt, to be the representative of a distinct
family.

   ENGRAULIS (including CETENGRAULIS).--Scales large or of moderate
   size. Snout more or less conical, projecting beyond the lower
   jaw. Teeth small or rudimentary. Intermaxillaries very small,
   hidden; maxillary long, attached to the cheek by a scarcely
   distensible membrane. Anal fin of moderate or great length.
   Branchiostegals short, from nine to fourteen in number.

Not less than forty-three different species of “Anchovies” are known
from temperate and tropical seas. They exhibit marked differences in
the length of their maxillary bone, which sometimes does not reach the
gill-opening, whilst in other species it extends far beyond it; and in
the number of their anal rays, which varies from 20 to 80. Some have
the upper pectoral ray prolonged into a filament, thus leading towards
the succeeding genus, _Coilia_. The majority are recognised, besides,
by their peculiar structure, by a broad silvery, lateral band, similar
to that observed in the Atherines. The most celebrated Anchovy is
_E. encrasicholus_, very plentiful in the Mediterranean, but rarely
wandering northwards. It is the species which, preserved in salt,
is exported to all parts of the world, although similarly lucrative
fisheries of Anchovies might be established in Tasmania where the same
species occurs, in Chile, China, Japan, California, at Buenos Ayres,
each of which countries possesses Anchovies by no means inferior to the
Mediterranean species.

   COILIA.--Body terminating in a long tapering tail. Scales of
   moderate size. Snout and jaws as in _Engraulis_. Anal fin
   exceedingly long, confluent with the caudal. The two or three
   upper pectoral rays are much prolonged, and their branches form
   four, six, or seven filaments.

  [Illustration: Fig. 300.--Coilia clupeoides.]

Ten species from Indian and Chinese seas.

   CHATOËSSUS.--Body compressed; abdomen serrated. Scales of
   moderate size. Snout obtuse, or obtusely conical, more or less
   projecting beyond the cleft of the mouth, which is narrow, more
   or less transverse. Maxillary joined to the ethmoid, its upper
   portion being behind the intermaxillary. Teeth none. Anal fin
   rather long; dorsal opposite to the ventrals, or to the space
   between ventrals and anal. Gill-membranes entirely separate;
   branchial arches forming two angles, one pointing forward and
   the other backwards; the fourth branchial arch with an accessory
   organ; branchiostegals of moderate length, five or six in number.

Ten species from the coasts, brackish and fresh waters of Central
America (one species ranges to New York), Australia, the East Indies,
and Japan.

   CLUPEA.--Body compressed, with the abdomen serrated, the
   serrature extending forwards to the thorax. Scales of moderate
   or large, rarely of small size. Upper jaw not projecting beyond
   the lower. Cleft of the mouth of moderate width. Teeth, if
   present, rudimentary and deciduous. Anal fin of moderate extent,
   with less than thirty rays; dorsal fin opposite to the ventrals.
   Caudal forked.

This genus comprises more than sixty different species, the
geographical distribution of which coincides with that of the family.
The majority are of greater or less utility to man, but a few tropical
species (_C. thrissa_, _C. venenosa_, and others) acquire, probably
from their food, highly poisonous properties, so as to endanger the
life of persons eating them. The most noteworthy species are--

1. _C. harengus_ (the “Herring”).--It is readily recognised by having
an ovate patch of very small teeth on the vomer. D. 17–20. A. 16–18.
L. lat. 53–59. Vert. 56. Gill-cover smooth, without radiating ridges.
It inhabits, in incredible numbers, the German Ocean, the northern
parts of the Atlantic, and the seas north of Asia. The Herring of the
Atlantic coasts of North America is identical with that of Europe. A
second species has been supposed to exist on the British coast (_C.
leachii_), but it comprises only individuals of a smaller size, the
produce of an early or late spawn. Also the so-called “White-bait” is
not a distinct species, but consists chiefly of the fry or the young
of herrings, and is obtained “in perfection” at localities where these
small fishes find an abundance of food, as in the estuary of the Thames.

   [Separate accounts on the Herring may be found in Cuvier
   and Valenciennes, “Hist. nat. des Poissons,” vol. xx.; J.
   M. Mitchell, “The Herring, its Natural History and National
   Importance,” Edinb. 1864, 8vo; P. Neucrantz, “De Harengo,”
   Lübeck, 1654; J. S. Dodd, “Essay towards a Natural History
   of the Herring,” Lond. 1768, 8vo; Bock, “Versuch einer
   vollstændigen Natur-und Handels-Geschichte des Hærings,”
   Königsberg, 1769, 8vo.]

2. _C. mirabilis._--The Herring of the North Pacific.

3. _C. sprattus._--The “Sprat.” Without vomerine teeth. D. 15–18.
A. 17–20. L. lat. 47–48. Vert. 47–49. Gill-cover, smooth, without
radiating ridges. Abundant on the Atlantic coasts of Europe.

4. _C. thrissa._--One of the most common West Indian fishes,
distinguished by the last dorsal ray being prolonged into a filament.
Hyrtl has discovered a small accessory branchial organ in this species.

5. _C. alosa._--The “Shad” or “Allice Shad,” with very fine and
long gill-rakers, from 60 to 80 on the horizontal part of the outer
branchial arch, and with one or more black lateral blotches. Coasts of
Europe, ascending rivers.

6. _C. finta._--The “Shad” or “Twaite Shad,” with stout osseous
gill-rakers, from 21 to 27 on the horizontal part of the outer
branchial arch, and spotted like the preceding species. Coasts of
Europe, ascending rivers, and found in abundance in the Nile.

7. _C. menhaden._--The “Mossbanker,” common on the Atlantic coasts
of the United States. The economic value of this fish is surpassed
in America only by that of the Gadoids, and derived chiefly from its
use as bait for other fishes, and from the oil extracted from it, the
annual yield of the latter exceeding that of the whale (from American
Fisheries). The refuse of the oil factories supplies a material of much
value for artificial manures.

   [See G. Brown Goode, “The Natural and Economical History of the
   American Menhaden,” in U.S. Commission of Fish and Fisheries,
   Part V., Washington, 1879, 8vo.]

8. _C. sapidissima._--The American Shad, abundant, and an important
food-fish on the Atlantic coasts of North America. Spawns in fresh
water.

9. _C. mattowocca._--The “Gaspereau” or “Ale-wife,” common on the
Atlantic coasts of North America, ascending into freshwater in early
spring, and spawning in ponds and lakes.

10. _C. pilchardus._--The “Pilchard” or the “Sardine,” equally
abundant in the British Channel, on the coast of Portugal, and in
the Mediterranean, and readily recognised by radiating ridges on the
operculum, descending towards the sub-operculum.

11. _C. sagax._--Representing the Pilchard in the Pacific, and found in
equally large shoals on the coasts of California, Chile, New Zealand,
and Japan.

12. _C. toli._--The subject of a very extensive fishery on the coast
of Sumatra for the sake of its roes, which are salted and exported to
China, the dried fish themselves being sent into the interior of the
island. The fish is called “Trubu” by the Malays, about 18 inches long,
and it is said that between fourteen and fifteen millions are caught
annually.

13. _C. scombrina._--The “Oil-Sardine” of the eastern coast of the
Indian Peninsula.

       *       *       *       *       *

Other, but less important genera of Clupeoids with serrated
abdomen, are _Clupeoides_, _Pellonula_, _Clupeichthys_, _Pellona_,
_Pristigaster_, and _Chirocentrodon_ (these three last with very small
or without any ventral fins).

   ALBULA.--Body oblong, moderately compressed; abdomen flat.
   Scales of moderate size, adherent; lateral line distinct. Eyes
   covered with a broad annular adipose membrane. Snout pointed,
   the upper jaw projecting beyond the lower. Mouth inferior, of
   moderate width, with villiform teeth; intermaxillary juxtaposed
   to the upper anterior edge of the maxillary. Dorsal fin opposite
   to the ventrals; anal fin shorter than dorsal. Gill-membranes
   entirely separate, with numerous branchiostegals.

One species only (_A. conorhynchus_), ranging over all tropical
and sub-tropical seas, and very common in many localities near the
coasts. It grows to a length of from two to three feet, and is not
valued as food.

   ELOPS.--Body rather elongate, moderately compressed; abdomen
   flat. Scales small, adherent; lateral line distinct. A narrow
   osseous lamella, attached to the mandibulary symphysis, covers
   the part between the mandibles. Snout pointed; mouth wide,
   anterior; intermaxillary short, maxillary forming the lateral
   part of the mouth. Bands of villiform teeth in the jaws, on the
   vomer, palatine and pterygoid bones, on the tongue, and on the
   base of the skull. Dorsal fin opposite to ventrals; anal rather
   shorter than dorsal. Gill-membranes entirely separate, with very
   numerous branchiostegals.

Two species, of which one, _E. saurus_, is, like the preceding fish,
spread over all tropical and sub-tropical seas; it exceeds a length of
three feet, and is not esteemed as food.

  [Illustration: Fig. 301.--Elops saurus.]

   MEGALOPS.--Body oblong, compressed, abdomen flat. Scales large,
   adherent; lateral line distinct. A narrow osseous lamella,
   attached to the mandibulary symphysis, between the mandibles.
   Snout obtusely conical; mouth anterior, lower jaw prominent;
   intermaxillary short; maxillary forming the lateral part of
   the mouth. Bands of villiform teeth in the jaws, on the vomer,
   palatine and pterygoid bones, on the tongue and on the base
   of the skull. Dorsal fin opposite to, or immediately behind,
   the ventrals; anal rather larger than dorsal. Gill-membranes
   entirely separate, with numerous branchiostegals. Pseudobranchiæ
   none.

Two species, one belonging to the Indo-Pacific (_M. cyprinoides_),
the other to the Atlantic (_M. thrissoides_); they are the largest
fishes of this family, exceeding a length of five feet, and excellent
eating. Young specimens enter freely fresh waters.

   CHANOS.--Body oblong, compressed; abdomen flat. Scales small,
   striated, adherent; lateral line distinct. Snout depressed;
   mouth small, anterior, transverse, the lower jaw with a small
   symphysial tubercle. Intermaxillary in juxtaposition to the
   upper anterior edge of maxillary. Teeth none. Dorsal fin
   opposite to the ventrals; anal small, shorter than dorsal;
   caudal deeply forked. Gill-membranes entirely united below, and
   free from the isthmus. Branchiostegals four, long. An accessory
   branchial organ in a cavity behind the gill-cavity proper.
   Air-bladder divided by a constriction into an anterior and
   posterior portion. Mucous membrane of the œsophagus raised in a
   spiral fold. Intestine with many convolutions.

Two species from the Indo-Pacific, of which _Ch. salmoneus_ is
extremely common; it enters fresh waters, and exceeds a length of four
feet; its flesh is highly esteemed. The accessory branchial organ and
the skeleton have been described by _Müller_, “Bau und Grenzen der
Ganoiden,” p. 75; and by _Hyrtl_, “Denkschr. Ak. Wiss. Wien.” xxi.
1883, p. 1.

       *       *       *       *       *

  [Illustration: Fig. 302.--Chanos salmoneus.]

The remaining genera belonging to this family are _Spratelloides_,
_Dussumieria_, and _Etrumeus_, which together form a small group,
distinguished by an anterior and lateral mouth, by the upper jaw not
overlapping the lower, by a rounded abdomen, and by lacking the gular
plate of some of the preceding genera.


                 TWENTY-THIRD FAMILY--BATHYTHRISSIDÆ.

_Body oblong, with rounded abdomen, covered with cycloid scales;
head naked; barbels none. Margin of the upper jaw formed by the
intermaxillaries mesially, and by the maxillaries laterally. Opercular
apparatus complete. Adipose fin none; dorsal fin much elongate, many
rayed; anal fin short. Stomach with a blind sac; pyloric appendages
numerous. Gill-apparatus well developed; pseudobranchiæ; gill-openings
wide; an air-bladder. Ova very small; ovaries without duct._

One genus and species only (_Bathythrissa dorsalis_) from deep water
(350 fathoms) off the coast of Japan. This remarkable fish has the
appearance of a _Coregonus_, and attains to a length of two feet.
Nothing is known of its osteology, but possibly a fossil genus from the
Gyps of Montmartre; _Notæus_, which has also a long dorsal fin, may
prove to belong to the same family.


                 TWENTY-FOURTH FAMILY--CHIROCENTRIDÆ.

_Body covered with thin, deciduous scales; barbels none. Margin
of the upper jaw formed by the intermaxillaries mesially, and by
the maxillaries laterally, both bones being firmly united, in
juxtaposition. Opercular apparatus complete. Adipose fin none; the
dorsal fin belongs to the caudal portion of the vertebral column.
Stomach with a blind sac; intestine short, the mucous membrane
forming a spiral fold; pyloric appendages none. Pseudobranchiæ none;
air-bladder incompletely divided into cells; gill-opening wide._

One genus and species only (_Chirocentrus dorab_) is known, which
is common in the Indian Ocean, and attains to a length of about
three feet; it is not esteemed as food. Remains of fishes similar to
_Chirocentrus_ are found in the marl slates of Padang, in Sumatra.


                 TWENTY-FIFTH FAMILY--ALEPOCEPHALIDÆ.

_Body with or without scales; head naked; barbels none. Margin of the
upper jaw formed by the intermaxillaries and maxillaries, the former
being placed along the upper anterior edge of the latter. Opercular
apparatus complete. Adipose fin none; the dorsal fin belongs to the
caudal portion of the vertebral column. Stomach curved, without blind
sac; pyloric appendages in moderate number. Pseudobranchiæ; air-bladder
absent. Gill-openings very wide._

Before the voyage of the “Challenger” one species only of this
family was known, _Alepocephalus rostratus_, a rare fish from the
Mediterranean; now, four genera with seven species are known, and there
is no doubt that this family is one of the most characteristic, and
will prove to be one of the most generally distributed forms, of the
deep-sea. Their vertical range varies between 345 (_Xenodermichthys_)
and 2150 (_Bathytroctes_) fathoms. They approach the Salmonoids, but
lack invariably the adipose fin. Their dentition is very feeble; their
eye large; bones thin. Coloration black.

   ALEPOCEPHALUS has thin cycloid scales; a mouth of moderate
   width, and no teeth on the maxillary.

   BATHYTROCTES has cycloid scales, a wide mouth, and teeth on the
   maxillary as well as intermaxillary.

   PLATYTROCTES has small keeled scales and no ventrals.

   XENODERMICHTHYS with fine nodules instead of scales.


                   TWENTY-SIXTH FAMILY--NOTOPTERIDÆ.

_Head and body scaly; barbels none. Margin of the upper jaw formed
by the intermaxillaries mesially, and by the maxillaries laterally.
Opercular apparatus incomplete. Tail prolonged, tapering. Adipose fin
none. Dorsal short, belonging to the caudal portion of the vertebral
column; anal very long. Stomach without blind sac; two pyloric
appendages. Pseudo__branchiae none; air-bladder present, divided
in the interior. The ova fall into the cavity of the abdomen before
exclusion. On each side a parieto-mastoid cavity leading into the
interior of the skull._

One genus only (_Notopterus_) with five species which inhabit fresh
waters of the East Indies and West Africa. Well-preserved remains
of this genus occur in the marl slates of Padang, in Sumatra. Their
air-bladder is divided into several compartments, and terminates in two
horns anteriorly and posteriorly, the anterior horns being in direct
connection with the auditory organ.


                  TWENTY-SEVENTH FAMILY--HALOSAURIDÆ.

_Body covered with cycloid scales; head scaly; barbels none. Margin
of the upper jaw formed by the intermaxillaries mesially, and by the
maxillaries laterally. Opercular apparatus incomplete. Adipose fin
none. The short dorsal belongs to the abdominal part of the vertebral
column; anal very long. Stomach with a blind sac; intestine short;
pyloric appendages in moderate number. Pseudobranchiæ none. Air-bladder
large, simple; gill-openings wide. Ovaries closed._

The only genus belonging to this family was discovered by the Madeiran
ichthyologist Johnson, in 1863; but since then the naturalists of the
“Challenger” expedition have added four other species, showing that
this type is a deep-sea form and widely distributed; the specimens were
dredged in depths varying from 560 to 2750 fathoms.


                 TWENTY-EIGHTH FAMILY--HOPLOPLEURIDÆ.

_Body generally with four series of subtriangular scutes, and with
intermediate scale-like smaller ones. One (?) dorsal only; head long,
with the jaws produced._

_Extinct_; developed in the chalk and extending into tertiary
formations: _Dercetis_ (with the upper jaw longest), _Leptotrachelus_,
_Pelargorhynchus_, _Plinthophorus_, _Saurorhamphus_ (with the lower jaw
longest), _Eurypholis_; _Ischyrocephalus_ (?). The latter genus, from
cretaceous formations of Westphalia, is said to have two dorsal fins.


                    TWENTY-NINTH FAMILY--GYMNOTIDÆ.

_Head scaleless; barbels none. Body elongate, eel-shaped. Margin
of the upper jaw formed in the middle by the intermaxillaries, and
laterally by the maxillaries. Dorsal fin absent or reduced to an
adipose strip; caudal generally absent, the tail terminating in a
point. Anal fin exceedingly long. Ventrals none. Extremity of the
tapering tail capable of being reproduced. Vent situated at, or at a
short distance behind, the throat. Humeral arch attached to the skull.
Ribs well developed. Gill-openings rather narrow. Air-bladder present,
double. Stomach with a cæcal sac and pyloric appendages. Ovaries with
oviducts._

Eel-like freshwater fishes from Tropical America.

   STERNARCHUS.--Tail terminating in a distinct small caudal fin.
   Teeth small. A rudimentary dorsal fin is indicated by an adipose
   band fitting into a groove on the back of the tail; it is easily
   detached, so as to appear as a thong-like appendage fixed in
   front. Branchiostegals four.

Eight species, some have the snout compressed and of moderate length,
like _St. Bonapartii_ from the River Amazons; others have it produced
into a long tube, as St. oxyrhynchus from the Essequibo.

   RHAMPHICHTHYS.--Caudal fin none; teeth none; no trace of a
   dorsal fin. No free orbital margin.

Six species, of which, again, some have a tubiform snout, whilst in the
others it is short.

   STERNOPYGUS.--Caudal fin none; no trace of a dorsal fin. Both
   jaws with small villiform teeth; similar teeth on each side of
   the palate. Body scaly.

Four species, very common, and growing to a length of 30 inches.

   CARAPUS.--Caudal fin none; no trace of a dorsal fin. A series of
   conical teeth in each jaw. Anterior nostrils, wide in the upper
   lip. Body scaly.

One species (_C. fasciatus_) extremely common, and found all over
tropical America, east of the Andes, from 18 to 24 inches long.

   GYMNOTUS.--Caudal and dorsal fins absent; anal extending to the
   end of the tail. Scales none. Teeth conical, in a single series.
   Eyes exceedingly small.

The “Electric Eel” is the most powerful of electric fishes, growing to
a length of six feet, and extremely abundant in certain localities of
Brazil and the Guyanas. The electric organ consists of two pairs of
longitudinal bodies, situated immediately below the skin, above the
muscles; one pair on the back of the tail, and the other pair along
the anal fin. Each fasciculus is composed of flat partitions or septa,
with transverse divisions between them. The outer edge of the septa
appear in nearly parallel lines in the direction of the longitudinal
axis of the body, and consist of thin membranes, which are easily torn;
they serve the same purpose as the columns in the analogous organ
of the Torpedo, making the walls or abutments for the perpendicular
and transverse dissepiments, which are exceedingly numerous, and so
closely aggregated as to seem almost in contact. The minute prismatic
cells, intercepted between these two sorts of plates, contain a
gelatinous matter; the septa are about one-thirtieth of an inch from
each other, and one inch in length contains a series of 240 cells,
giving an enormous surface to the electric organs. The whole apparatus
is supplied with more than 200 nerves, which are the continuations of
the rami anteriores of the spinal nerves. In their course they give out
branches to the muscles of the back, and to the skin of the animal.
In the Gymnotus, as in the Torpedo, the nerves supplying the electric
organs are much larger than those bestowed on any part for the purposes
of sensation or movement.

The graphic description by Humboldt of the capture of Electric Eels
by horses driven into the water, which would receive the electric
discharges and thus exhaust the fishes, seems to rest either on the
imagination of some person who told it to the great traveller or on
some isolated incident. Recent travellers have not been able to verify
it even in the same parts of the country where the practice was said to
exist.


                    THIRTIETH FAMILY--SYMBRANCHIDÆ.

_Body elongate, naked or covered with minute scales; barbels none.
Margin of the upper jaw formed by the intermaxillaries only, the well
developed maxillaries lying behind and parallel to them. Paired fins
none. Vertical fins rudimentary, reduced to more or less distinct
cutaneous folds. Vent situated at a, great distance behind the head.
Ribs present. Gill-openings confluent into one slit situated on the
ventral surface. Air-bladder none. Stomach without cæcal sac or pyloric
appendages. Ovaries with oviducts._

The fishes of this family consist of freshwater-fishes from tropical
America and Asia, which, however, enter also brackish water; and of a
truly marine genus from Australia.

   AMPHIPNOUS.--Vent in the posterior half of the body, which is
   covered with minute scales longitudinally arranged.

A common fish (_A. cuchia_) in Bengal, remarkable for its singular
respiratory apparatus. It has only three branchial arches, with
rudimentary branchial laminæ, and with very narrow slits between the
arches. To supplement this insufficient respiratory apparatus, a
lung-like sac is developed on each side of the body behind the head,
opening between the hyoid and first branchial arch. The interior of the
sac is abundantly provided with blood-vessels, the arterial coming from
the branchial arteries, whilst those issuing from it unite to form the
aorta. _A. cuchia_ approaches the Eels in having the humeral arch not
attached to the skull.

   MONOPTERUS.--Vent in the posterior half of the body, which
   is naked. Three branchial arches with rudimentary gills, but
   without breathing sac.

One species (_M. javanicus_), which is extremely common in the East
Indian Archipelago and in the eastern parts of the Continent. Upwards
of three feet long.

   SYMBRANCHUS.--Vent in the posterior half of the body, which is
   naked. Four branchial arches with well developed gills.

Three species, of which one (_S. marmoratus_) is extremely common in
tropical America, and the other (_S. bengalensis_) not less so in the
East Indies.

   CHILOBRANCHUS.--Vent in the anterior half of the length of
   the body, which is naked. Vertical fins reduced to a simple
   cutaneous fold, without rays.

A small fish (_Ch. dorsalis_) from North Western Australia and Tasmania.


                    THIRTY-FIRST FAMILY--MURÆNIDÆ.

_Body elongate, cylindrical or “band-shaped, naked or with
rudimentary scales. Vent situated at a great distance from the head.
Ventral fins none. Vertical fins, if present, confluent, or separated
by the projecting tip of the tail. Sides of the upper jaw formed by the
tooth-bearing maxillaries, the fore part by the intermaxillary, which
is more or less coalescent with the vomer and ethmoid. Humeral arch not
attached to the skull. Stomach with a blind sac; no pyloric appendages.
Organs of reproduction without efferent ducts._

The “Eels” are spread over almost all fresh waters and seas of the
temperate and tropical zones; some descend to the greatest depths
of the oceans. The young of some have a limited pelagic existence.
(_Leptocephali_, see p. 179.) At Monte Bolca fossil remains are very
numerous, belonging to recent genera, _Anguilla_, _Sphagebranchus_, and
_Ophichthys_; even larval Leptocephales have been preserved. _Anguilla_
has been found also in the chalk of Aix and Oeningen.

In the majority of the species the branchial openings in the pharynx
are wide slits (_Murænidæ platyschistæ_); in others, the true Murænæ,
(_Murænidæ engyschistæ_) they are narrow.

   NEMICHTHYS.--Exceedingly elongate, band-shaped; tail tapering
   into a point. Vent approximate to the pectorals, but the
   abdominal cavity extending far behind the vent. Jaws produced
   into a long slender bill, the upper part being formed by the
   vomer and intermaxillaries. The inner surface of the bill
   covered with small tooth-like asperities. Eye large. The
   nostrils of each side are close together, in a hollow before the
   eye. Gill-openings wide, nearly confluent. Pectoral and vertical
   fins well developed.

This very singular type is a deep-sea form, occurring at depths of from
500 to 2500 fathoms. The two species known have hitherto been found in
the Atlantic only.

   CYEMA.--This genus combines the form of the snout of
   _Nemichthys_, with the soft and shorter body of a
   _Leptocephalus_; but the gill-openings are very narrow and close
   together on the abdominal surface. Vent in about the middle of
   the length of the body; vertical fins well developed, confined
   to, and surrounding, the tail. Pectoral fins well developed. Eye
   very small.

Known from two specimens only, 4½ inches long, dredged in depths of
1500 and 1800 fathoms in the Pacific and Antarctic Oceans.

   SACCOPHARYNX.--Deep-sea Congers, with the muscular system
   very feebly developed, with the bones very thin, soft, and
   wanting in inorganic matter. Head and gape enormous. Snout
   very short, pointed, flexible, like an appendage overlapping
   the gape. Maxillary and mandibulary bones very thin, slender,
   arched, armed with one or two series of long, slender, curved,
   widely set teeth, their points being directed inwards; palate
   toothless. Gill-openings wide, at some distance from the head,
   at the lower part of the sides; gills very narrow, free, and
   exposed. Trunk of moderate length. Stomach distensible in
   an extraordinary degree. Vent at the end of the trunk. Tail
   band-like, exceedingly long, tapering in a very fine filament.
   Pectoral small, present. Dorsal and anal fins rudimentary.

This is another extraordinary form of Deep-sea Eels; the muscular
system, except on the head, is very feebly developed; the bones are as
thin, soft, and wanting in inorganic matter, as in the _Trachypteridæ_.
This fish is known from three specimens only, which have been found
floating on the surface of the North Atlantic, with their stomachs much
distended, having swallowed some other fish, the weight of which many
times exceeded that of their destroyer. It attains to the length of
several feet.

   SYNAPHOBRANCHUS.--Gill-openings ventral, united into a
   longitudinal slit between the pectoral fins, separate
   internally. Pectoral and vertical fins well developed. Nostrils
   lateral, the anterior subtubular, the posterior round, before
   the lower half of the eye. Cleft of the mouth very wide; teeth
   small; body scaly. Stomach very distensible.

Deep-sea Congers, with well-developed muscular system, spread over
all oceans, and occurring in depths of from 345 to 2000 fathoms. Four
species are known. Probably attaining to the same length as the Conger.

   ANGUILLA.--Small scales imbedded in the skin. Upper jaw not
   projecting beyond the lower. Teeth small, forming bands.
   Gill-openings narrow, at the base of the pectoral fins. The
   dorsal fin commences at a considerable distance from the occiput.

Some twenty-five species of “Eels” are known from the freshwaters and
coasts of the temperate and tropical zones; none have been found in
South America or the west coast of North America and West Africa.
The following are the most noteworthy:--The common European species
(_A. anguilla_) is spread over Europe to 64° 30´ lat. N., and all
round the Mediterranean area, but is not found either in the Danube
or in the Black and Caspian Seas; it extends across the Atlantic to
North America. The form of the snout varies much, and some naturalists
have believed that specimens with a broad and obtuse snout were
specifically distinct from those with pointed snout. However, every
degree of breadth of the snout may be observed; and a much safer
way of recognizing this species, and distinguishing it from other
European Eels, is the forward position of the dorsal fin; the distance
between the commencement of the dorsal and anal fins being as long as,
or somewhat longer than, the head. Eels grow generally to a length
of about three feet, but the capture of much larger examples is on
record. Their mode of propagation is still unknown. So much only is
certain that they do not spawn in fresh water, that many full-grown
individuals, but not all, descend rivers during the winter months, and
that some of them at least must spawn in brackish water or in deep
water in the sea; for in the course of the summer young individuals
from three to five inches long ascend rivers in incredible numbers,
overcoming all obstacles, ascending vertical walls or floodgates,
entering every larger and smaller tributary, and making their way
even over terra firma to waters shut off from all communication
with rivers. Such immigrations have been long known by the name of
“_Eel-fairs_.” The majority of the Eels which migrate to the sea
appear to return to fresh water, but not in a body, but irregularly,
and throughout the warmer part of the year. No naturalist has ever
observed these fishes in the act of spawning, or found mature ova; and
the organs of reproduction of individuals caught in fresh water are
so little developed and so much alike, that the female organ can be
distinguished from the male only with the aid of a microscope.

The second species found in Great Britain, on the coasts of Europe
generally, in China, New Zealand, and the West Indies, is (_A.
latirostris_) the “Grig” or “Glut,” which prefers the neighbourhood of
the sea to distant inland-waters, and in which the dorsal fin begins
farther backwards, the distance between the commencement of the dorsal
and anal fins being shorter than the head; its snout seems to be always
broad. On the American side of the Atlantic other species, beside _A.
anguilla_ are found in abundance: _A. bostoniensis_, _A. texana_.
The largest Eels occur in lakes of the islands of the Indo-Pacific,
and they play a conspicuous part in the mythology of the South-Sea
Islanders and Maories; individuals of from eight to ten feet in length
have been seen, and referred to several species, as _A. mauritiana_,
_fidjiensis_, _obscura_, _aneitensis_, etc.

   CONGER.--Scaleless. Cleft of the mouth wide, extending at least
   to below the middle of the eye. Maxillary and mandibulary
   teeth arranged in series, one of which contains teeth of equal
   size, and so closely set as to form a cutting edge. No canine
   teeth. Vomerine band of teeth short. Pectoral and vertical fins
   well developed, the dorsal commencing behind the root of the
   pectoral. Gill-openings large, approximate to the abdomen. The
   posterior nostril opposite to the upper or middle part of the
   orbit, the anterior in a tube. Eyes well developed.

The “Congers” are marine Eels; the best known species (_C. conger_)
seems to be almost cosmopolitan, and is plentiful all round Europe, at
St. Helena, in Japan, and Tasmania. It attains to a length of eight
feet, and thrives and grows rapidly even in confinement, which is
not the case with the freshwater Eel. Three other species are known,
of which _C. marginatus_ from the Indian Ocean, is the most common.
_Leptocephalus morrisii_ is an abnormal larval condition of the Conger.

Genera allied to _Conger_ are _Poeciloconger_, _Congromurcæna_,
_Uroconger_, and _Heteroconger_.

   MURÆNESOX.--Scaleless. Snout produced. Jaws with several series
   of small closely set teeth, anteriorly with canines; vomer with
   several long series of teeth, the middle of which is formed
   by large conical or compressed teeth. Gill-openings wide,
   approximate to the abdomen. Pectoral and vertical fins well
   developed, the dorsal beginning above the gill-opening. Two
   pairs of nostrils, the posterior opposite to the upper part or
   middle of the eye.

Four species from tropical seas, _M. cinereus_ being very common in the
Indian Ocean, and attaining to a length of six feet.

   NETTASTOMA.--Scaleless. Snout much produced, depressed. Jaws
   and vomer with bands of card-like teeth, those along the median
   line of the vomer being somewhat the larger. Vertical fins well
   developed; pectorals none. Gill-openings of moderate width,
   open. Nostrils on the upper surface of the head, valvular; the
   anterior near to the end of the snout, the posterior above the
   anterior angle of the eye.

This genus lives at some depth, the Japanese species (_N. parviceps_)
having been obtained at 345 fathoms. _N. melanurum_ from the
Mediterranean, seems to inhabit a similar depth. _Hyoprorus_ is its
Leptocephalid form.

Genera allied to _Murcænesox_ are _Saurenchelys_, _Oxyconger_,
_Hoplunnis_, and _Neoconger_; in all these the nostrils have a
superior or lateral position. In other genera the nostrils perforate
the upper lip, as in _Myrus_, _Myrophis_, _Paramyrus_, _Chilorhinus_,
_Murænichthys_, and _Ophichthys_, the last genus deserving of
particular mention on account of its great range and common occurrence.

   OPHICHTHYS.--Nostrils labial; extremity of the tail free, not
   surrounded by a fin.

More than eighty species are known, many of which are abundant on the
coasts of the tropical and sub-tropical zones. They do not attain to
a large size, but many must be extremely voracious and destructive to
other fishes, if we draw an inference from the formidable dentition
with which their jaws and palate is armed. Other species have much
more feeble, and some even obtuse teeth, better adapted for seizing
Crustaceans than vigorous and slippery fishes. Some have rudimentary
pectoral fins or lack them altogether. Many are highly ornamented with
bands or spots, the coloration being apparently very constant in the
several species.

  [Illustration: Fig. 303.--Ophichthys crocodilinus, from the
  Indo-Pacific.]

   MORINGUA.--Body scaleless, cylindrical, with the trunk much
   longer than the tail. Pectorals none or small; vertical fins
   but little developed, limited to the tail. Posterior nostrils
   in front of the small eye. Cleft of the mouth narrow; teeth
   uniserial. Heart placed far behind the branchiæ. Gill-openings
   rather narrow, inferior.

Six species from freshwaters, brackish water, and the coasts of India
to the Fiji Islands.

   MURÆNA.--Scaleless. Teeth well developed. Gill-openings and
   clefts between the branchial arches narrow. Pectoral fins none;
   dorsal and anal fins well developed. Two nostrils on each side
   of the upper surface of the snout; the posterior a narrow round
   foramen, with or without tube; the anterior in a tube.

  [Illustration: Fig. 304.--Head of a Muræna.]

  [Illustration: Fig. 305.--Muræna pavonina, from Southern Seas.]

The Murænas are as abundantly represented in the tropical and
sub-tropical zones, and have nearly the same range, as _Ophichthys_.
The number of species known exceeds eighty. The majority are armed
with formidable pointed teeth, well suited for seizing other fish on
which they prey. Large specimens thus armed readily attack persons in
and out of the water; and as some species attain a length of some six
or eight feet, they are justly feared by fishermen. The minority of
species have obtuse and molar-like teeth, their food consisting chiefly
of Crustaceans and other hard-shelled animals. Most of the Murænas
are beautifully coloured and spotted, some in a regular and constant
manner, whilst in others the pattern varies in a most irregular
fashion: they have quite the appearance of snakes. The Muræna of
the Ancient Romans is _Muræna helena_, which is not confined to the
Mediterranean, but also found in the Indian Ocean and on the coast of
Australia. Its skin is of a rich brown, beautifully marked with large
yellowish spots, each of which contains smaller brown spots.

  [Illustration: Fig. 306.--Muræna picta, from the Indo-Pacific.]

_Gymnomuræna_ differs from _Muræna_ in having the fins reduced to a
short rudiment near the end of the tail. Six species are known growing
to a length of eight feet.

  [Illustration: Fig. 307.--Gymnomuræna vittata, from Cuba.]

_Myroconger_ and _Enchelycore_ belong to the same sub-family as
_Muræna_, but the former is provided with pectoral fins, and in the
latter the posterior nostril is a long slit, and not round as in the
other genera.


                      FIFTH ORDER--LOPHOBRANCHII.

_The gills are not laminated, but composed of small rounded lobes
attached to the branchial arches. Gill-cover reduced to a large simple
plate. Air-bladder simple, without pneumatic duct. A dermal skeleton
composed of numerous pieces arranged in segments, replaces more or less
soft integuments. Muscular system not much developed. Snout prolonged.
Mouth terminal, small, toothless, formed as in Acanthopterygians._

  [Illustration: Fig. 308.--Gills of Hippocampus abdominalis.]


                     FIRST FAMILY--SOLENOSTOMIDÆ.

_Gill-openings wide. Two dorsal fins, the rays of the anterior not
articulated. All the other fins well developed._

One living genus only is known, which was preceded in the tertiary
epoch by _Solenorhynchus_ (Monte Postale).

   SOLENOSTOMA.--Snout produced into a long tube. Body compressed,
   with very short tail. All parts covered with thin skin, below
   which there is a dermal skeleton formed by large star-like
   ossifications. The soft dorsal and anal fins on elevated
   bases; caudal fin long. Ventral fins inserted opposite to the
   anterior dorsal, close together, seven-rayed; they are free in
   the male, but in the female their inner side coalesces with the
   integuments of the body, a large pouch for the reception of
   the eggs being formed thereby. Air-bladder and pseudobranchiæ
   absent. Branchiostegals four, very thin. Intestinal tract very
   simple, with a stomachic dilatation, without pyloric appendages.
   Ova very small.

The dermal skeleton of this singular type is formed by star-like
ossifications, four in each horizontal and vertical series on the side
of the fore part of the trunk; each consists of four or three radiating
branches by which it joins the neighbouring bones; on the hind part
of the trunk and tail the series are diminished to two. The dorsal
and abdominal profiles in front of the fins are protected by similar
bones. The vertebral column is composed of eighteen abdominal and
fifteen caudal vertebræ, the vertebræ gradually decreasing in length
backwards, so that the shortness of the tail is caused not only by
the smaller number of vertebræ, but also by their much lesser length.
Neural and hæmal spines are developed. The pelvis consists of two pairs
of cartilaginous laminæ, the convex margin of the anterior fitting
into an angle of a dermal bone which separates the pelvis from the
well-ossified humeral arch.

The singular provision for the retention and protection of the eggs has
been described above (p. 162, figs. 73 and 74), and we have only to
repeat here that it is the female which takes care of the progeny, and
not the male as in the following family. Two or three small species are
known from the Indian Ocean; they are beautifully marked, especially
the male, which also appears to be of smaller size in this genus than
the female.


                      SECOND FAMILY--SYNGNATHIDÆ.

_Gill-openings reduced to a very small opening near the upper
posterior angle of the gill-cover. One soft dorsal fin; no ventrals,
and, sometimes, one or more of the other fins are also absent._

Small marine fishes, which are abundant on such parts of the coasts
of the tropical and temperate zones as offer by their vegetation
shelter to these defenceless creatures. They are bad swimmers (the
dorsal fin being the principal organ of locomotion), and frequently
and resistlessly carried by currents into the open ocean or to distant
coasts. All enter brackish water, some fresh water. The strata of Monte
Bolca and Licata (Sicily) have, yielded evidence of their existence in
the tertiary epochs; beside species of _Siphonostoma_ and _Syngnathus_
(_Pseudosyngnathus_), remains of an extinct genus, _Calamostoma_,
allied to _Hippocampus_, but with a distinct caudal fin, have been
found. On their propagation see p. 163, Fig. 76.

   A. SYNGNATHINA.--The tail is not prehensile, and generally
   provided with a caudal fin.--_Pipe-Fishes._

   SIPHONOSTOMA.--Body with distinct ridges, the upper caudal
   ridge continuous with the lateral line, but not with the dorsal
   ridge of the trunk. Pectoral and caudal fins well developed;
   dorsal fin of moderate length, opposite to the vent. Humeral
   bones movable, not united into a “breast-ring.” Males with an
   egg-pouch on the tail, the eggs being covered by cutaneous folds.

Two species, of which _S. typhle_ is common on the British, and
generally distributed on the European coasts.

   SYNGNATHUS.--Body with the ridges more or less distinct, the
   dorsal ridge of the trunk not being continuous with that of the
   tail. Pectoral fins well developed; caudal present. Dorsal fin
   opposite or near to the vent. Humeral bones firmly united into
   the breast-ring. Egg-pouch as in _Siphonostoma_.

The distribution of this genus nearly coincides with that of the
family, some fifty species being known. _S. acus_, the great Pipe-fish
(see Fig. 75, p. 163), is one of the most common European fishes,
extending across the Atlantic and southwards to the Cape of Good
Hope; it attains a length of 18 inches. Another very common species,
frequently met at sea, and spread over nearly all the tropical and
sub-tropical seas, is _S. pelagicus_, agreeably marked with alternate
brown and silvery cross-bars.

   DORYICHTHYS.--Body with the ridges well developed. Pectoral and
   caudal fins present. Dorsal fin long or of moderate length,
   opposite to the vent. Humeral bones firmly united. Males with
   the lower ridges of the abdomen dilated, the dilated parts
   forming a broad groove for the reception of the ova.

In these Pipe-fishes the ova are not received in a completely closed
pouch, but glued on to the surface of the abdomen. Twenty species from
tropical seas.

   NEROPHIS.--Body smooth, rounded, with scarcely any of the ridges
   distinct. Pectoral fin none, caudal absent or rudimentary, the
   tail tapering into a point. Dorsal fin of moderate length,
   opposite to the vent. The ova are attached to the soft
   integument of the abdomen of the male, and are not covered by
   lateral folds of the skin.

Seven species from the European seas and the Atlantic. _N. æquoreus_
(Ocean Pipe-fish), _N. ophidion_ (Straight-nosed Pipe-fish), and _N.
lumbriciformis_ (Little Pipe-fish), are common on the British coasts.

   PROTOCAMPUS.--The whole dermal skeleton is covered with skin.
   A broad cutaneous fold runs along the back in front and behind
   the dorsal; a similar fold along the abdomen. Pectoral fin none;
   caudal very small.

The single species of this remarkable genus, _P. hymenolomus_, occurs
in the Falkland Islands. It may be regarded as an embryonal form of
_Nerophis_, the median skin-folds being evidently remains of the fringe
which surrounds the body of the embryo.

The other genera belonging to this group are, _Icthyocampus_,
_Nannocampus_, _Urocampus_, _Leptoichthys_, _Coelonotus_, and
_Stigmatophora_.

   HIPPOCAMPINA.--The tail is prehensile, and invariably without
   caudal fin.--_Sea-horses._

   GASTROTOKEUS.--Body depressed, the lateral line running along
   the margin of the abdomen. Shields smooth. Tail shorter than the
   body. Pectoral fins. No pouch is developed for the ova, which
   are imbedded in the soft integument of the abdomen of the male.

_Gastrotokeus biaculeatus_, very common in the Indian Ocean to the
coasts of Australia.

   SOLENOGNATHUS.--Body compressed, deeper than broad. Shields
   hard, rugose, with round or oval interannular plates; and
   without elongate processes. Tail shorter than the body. Pectoral
   fins.

Three species, from the Chinese and Australian Seas; they are the
largest of Lophobranchs, _S. hardwickii_, attaining to a length of
nearly two feet.

  [Illustration: Fig. 309.--Phyllopteryx eques.]

   PHYLLOPTERYX.--Body compressed, or as broad as deep. Shields
   smooth, but some or all of them are provided with prominent
   spines or processes on the edges of the body; some of the
   processes with cutaneous filaments. A pair of spines on the
   upper side of the snout and above the orbit. Tail about as
   long as the body. Pectoral fins. The ova are imbedded in soft
   membrane on the lower side of the tail, without a pouch being
   developed.

Three species from the coasts of Australia. The protective resemblances
with which many Lophobranchs are furnished, attain to the highest
degree of development in the fishes of this genus. Not only their
colour closely assimilates that of the particular kind of seaweed which
they frequent, but the appendages of their spines seem to be merely
part of the fucus to which they are attached. They attain a length of
12 inches.

   HIPPOCAMPUS.--Trunk compressed, more or less elevated. Shields
   with more or less prominent tubercles or spines. Occiput
   compressed into a crest, terminating at its supero-posterior
   corner in a prominent knob (coronet). Pectoral fins. The males
   carry the eggs in a sac at the base of the tail, opening near
   the vent.

A singular resemblance of the head and fore part of the body to that
of a horse, has given to these fishes the name of “Sea-horses.” They
are abundant between and near the tropics, becoming scarcer in higher
latitudes. Some twenty species are known, some of which have a wide
geographical range, as they are often carried to great distances with
floating objects to which they happen to be attached.--_Acentronura_ is
a genus closely allied to _Hippocampus_.


                      SIXTH ORDER--PLECTOGNATHI.

_Teleosteous fishes with rough scales, or with ossifications of the
cutis in the form of scutes or spines; skin sometimes entirely naked.
Skeleton incompletely ossified, with the vertebræ in small number.
Gills pectinate; a narrow gill-opening in front of the pectoral fins.
Mouth narrow; the bones of the upper jaw generally firmly united. A
soft dorsal fin, belonging to the caudal portion of the vertebral
column, opposite to the anal; sometimes elements of a spinous dorsal
besides. Ventral fin none, or reduced to spines. Air-bladder without
pneumatic duct._


                      FIRST FAMILY--SCLERODERMI.

_Snout somewhat produced; jaws armed with distinct teeth in small
number. Skin with scutes or rough. The elements of a spinous dorsal and
ventral fins generally present._

Marine fishes of moderate or small size, very common in the tropical
zone, but scarcer in higher latitudes. They have been found in three
localities of tertiary strata, viz., at Monte Bolca, where a species of
_Ostracion_ occurs, and in the Schists of Glaris, from which two genera
have been described, _Acanthoderma_ and _Acanthopleurus_, closely
allied to _Balistes_ and _Triacanthus_. _Glyptocephalus_ from the Isle
of Sheppey has the skull of a Balistes, but its body is covered with
tubercles arranged in regular series. The Scleroderms may be divided
into three very natural groups:--

   A. TRIACANTHINA.--The skin is covered with small, rough,
   scale-like scutes. A spinous dorsal fin with from four to six
   spines. A pair of strong, movable ventral spines, joined to the
   pelvic bone.

To this group belong the genera _Triacanthodes_, _Hollardia_, and
_Triacanthus_, represented by five species, of which _Triacanthus
brevirostris_ from the Indian Ocean is the most common.

   B. BALISTINA.--Body compressed, covered with movable scutes or
   rough. Spinous dorsal reduced to one, two, or three spines.
   Ventral fins reduced to a single pelvic prominence, or entirely
   absent.

To this group belong the genera _Balistes_, _Monacanthus_, and
_Anacanthus_, the last genus being distinguished by a barbel at the
lower jaw.

  [Illustration: Fig. 310.--Balistes vidua.]

_Balistes_, or the “File-fishes” proper, inhabit the tropical and
sub-tropical seas; shoals of young are not rarely met with in
mid-ocean. Some thirty species are known, many attaining a length
exceeding two feet; but the majority are much smaller, and frequently
beautifully and symmetrically marked. Both jaws are armed with eight
strong incisor-like and obliquely truncated teeth, by which these
fishes are enabled to break off pieces of corals on which they feed,
or to chisel a hole into the hard shell of Mollusca, in order to
extract the soft parts. They destroy an immense number of Mollusks,
thus becoming most injurious to the pearl-fisheries. The first of their
three dorsal spines is very strong, roughened in front like a file,
and hollowed out behind to receive the second much smaller spine,
which, besides, has a projection in front, at its base, fitting into
a notch of the first. Thus these two spines can only be raised or
depressed simultaneously, and the first cannot be forced down, unless
the second has been previously depressed. The latter has been compared
to a trigger, hence a second name, “Trigger-fish,” has been given to
these fishes. Some species are armed with a series of short spines or
tubercles on each side of the tail. Two species (_B. maculatus_ and _B.
capriscus_), common in the Atlantic, sometimes wander to the British
coasts.

The _Monacanthus_ are similarly distributed as the _Balistes_, and
still more abundant, some fifty species being known. Their dentition
is very similar, but they possess one dorsal spine only, and their
rough scales are so small as to give a velvety appearance to the skin
(Figs. 17 and 18, p. 48). Adult males of some of the species possess a
peculiar armature on each side of the tail, which in females is much
less developed or entirely absent. This armature may consist either in
simple spines arranged in rows, or in the development of the minute
spines of the scales into long stiff bristles, so that the patch on
each side of the tail looks like a brush.

   C. OSTRACIONTINA.--The integuments of the body form a hard
   continuous carapace, consisting of hexagonal scutes juxtaposed
   in mosaic-fashion. A spinous dorsal and ventral fins are absent;
   but sometimes indicated by protuberances.

The “Coffer-fishes” (_Ostracion_) are too well known to require a
lengthened description. Only the snout, the bases of the fins, and the
hind part of the tail are covered with soft skin, so as to admit of
free action of the muscles moving these parts. The mouth is small, the
maxillary and intermaxillary bones coalescent, each jaw being armed
with a single series of small slender teeth. The short dorsal fin is
opposite to the equally short anal. The vertebral column consists of
fourteen vertebræ only, of which the five last are extremely short,
the anterior elongate. Ribs none. The carapaces of some species are
three-ridged, of others four- and five-ridged, of some provided with
long spines. Twenty-two species from tropical and sub-tropical seas are
known.


                      SECOND FAMILY--GYMNODONTES.

_Body more or less shortened. The bones of the upper and lower
jaw are confluent, forming a beak with a trenchant edge, without
teeth, with or without median suture. A soft dorsal, caudal and anal
are developed, approximate. No spinous dorsal. Pectoral fins; no
ventrals._

Marine fishes of moderate or small size from tropical and sub-tropical
seas. A few species live in fresh water. Fossil remains of
_Diodon_ are not scarce at Monte Bolca and Licata; a distinct
genus, _Enneodon_, has been described from Monte Postale. The
Gymnodonts may be divided into three groups:

   A. TRIODONTINA.--Tail rather long, with a separate caudal fin.
   Abdomen dilatable into a very large, compressed, pendent sac,
   the lower part of which is merely a flap of skin, into which the
   air does not penetrate, the sac being capable of being expanded
   by the very long pelvic bone. The upper jaw divided by a median
   suture, the lower simple.

A single genus and species (_Triodon bursarius_) from the Indian
Ocean.

   B. TETRODONTINA.--Tail and caudal fin distinct. Part of the
   œsophagus much distensible, and capable of being filled with
   air. No pelvic bone.

“Globe-fishes” have a short, thick, cylindrical body, with well
developed fins. It is covered with thick scaleless skin, in which,
however, spines are imbedded of various sizes. The spines are very
small, and but partially distributed over the body in some species,
whilst in others they are very large, and occupy equally every part
of the body. These fishes have the power of inflating their body by
filling their distensible œsophagus with air, and thus assume a more or
less globular form. The skin is, then, stretched to its utmost extent,
and the spines protrude and form a more or less formidable defensive
armour, as in a hedgehog; therefore they are frequently called
“Sea-hedgehogs.” A fish thus blown out turns over and floats belly
upwards, driving before the wind and waves. However, it is probable
that the spines are a protection not only when the fish is on the
surface and able to take in air, but also when it is under water. Some
Diodonts, at any rate, are able to erect the spines about the head by
means of cutaneous muscles; and, perhaps, all fill their stomach with
water instead of air, for the same purpose and with the same effect. In
some Diodonts the spines are fixed, erect, not movable. The Gymnodonts
generally, when taken, produce a sound, doubtless by the expulsion
of air from the œsophagus. Their vertebral column consists of a small
number of vertebræ, from 20 to 29, and their spinal chord is extremely
short. All these fishes have a bad reputation, and they are never
eaten; indeed, some of them are highly poisonous, and have caused long
continued illness and death. Singularly, the poisonous properties of
these fishes vary much as regards intensity, only certain individuals
of a species, or individuals from a certain locality, or caught at a
certain time of the year, being dangerous. Therefore it is probable
that they acquire their poisonous quality from their food, which
consists in corals and hard-shelled Mollusks and Crustaceans. Their
sharp beaks, with broad masticating posterior surface, are admirably
adapted for breaking off branchlets of coral-stocks, and for crushing
hard substances.

  [Illustration: Fig. 311.--Jaws of Tetrodon.]

  [Illustration: Fig. 312.--Tetrodon margaritatus.]

   TETRODON (including _Xenopterus_).--Both the upper and lower
   jaws are divided into two by a mesial suture.

Extremely numerous in tropical and sub-tropical zones, more than
sixty species being known. In some of the species the dermal
spines are extremely small, and may be absent altogether. Many are
highly ornamented with spots or bands. A few species live in large
rivers--thus _T. psittacus_ from Brazil; _T. fahaka_, a fish well
known to travellers on the Nile, and likewise abundant in West African
rivers; _T. fluvi__atilis_ from brackish water and rivers of the East
Indies. The species figured is one of the smallest, about six inches
long, and common in the Indo-Pacific.

   DIODON.--Jaws without mesial suture, so that there is only one
   undivided dental plate above and one below.

In these fishes, as well as in some closely allied genera, the dermal
spines are much more developed than in the Tetrodonts; in some the
spines are erectile, as in _Diodon_, _Atopomycterus_, _Trichodiodon_,
and _Trichocyclus_; in others they are stiff and immovable, as in
_Chilomycterus_ and _Dicotylichthys_. Seventeen species are known, of
which _Diodon hystrix_ is the most common as it is the largest, growing
to a length of two feet. It is spread over the Tropical Atlantic as
well as Indo-Pacific, as is also a smaller, but almost equally common
species, _Diodon maculatus_.

  [Illustration: Fig. 313.--Diodon maculatus.]

  [Illustration: Fig. 314.--Diodon maculatus, inflated.]

   C. MOLINA.--Body compressed, very short; tail extremely short,
   truncate. Vertical fins confluent. No pelvic bone.

The “Sun-fishes” (_Orthagoriscus_) are pelagic fishes, found in every
part of the oceans within the tropical and temperate zones. The
singular shape of their body and the remarkable changes which they
undergo with age, have been noticed above (p. 175, Figs. 93, 94).
Their jaws are undivided in the middle, comparatively feeble, but well
adapted for masticating their food, which consists of small pelagic
Crustaceans. Two species are known. The common Sun-fish, _O. mola_,
which attains to a very large size, measuring seven or eight feet, and
weighing as many hundredweights. It has a rough, minutely granulated
skin. It frequently approaches the southern coasts of England and the
coasts of Ireland, and is seen basking in calm weather on the surface.
The second species, _O. truncatus_, is distinguished by its smooth,
tessellated skin, and one of the scarcest fishes in collections. The
shortness of the vertebral column of the Sun-fishes, in which the
number of caudal vertebra is reduced to seven, the total number being
seventeen, and the still more reduced length of the spinal chord have
been noticed above (p. 96).


                    THIRD SUB-CLASS--CYCLOSTOMATA.

_Skeleton cartilaginous and notochordal, without ribs and without
real jaws. Skull not separate from the vertebral column. No limbs.
Gills in the form of fixed sacs, without branchial arches, six or seven
in number on each side. One nasal aperture only. Heart without bulbus
arteriosus. Mouth anterior, surrounded by a circular or subcircular
lip, suctorial. Alimentary canal straight, simple, without coecal
appendages, pancreas or spleen. Generative outlet peritoneal. Vertical
fins rayed._

The Cyclostomes are most probably a very ancient type. Unfortunately
the organs of these creatures are too soft to be preserved, with the
exception of the horny denticles with which the mouth of some of them
is armed. And, indeed, dental plates, which are very similar to those
of _Myxine_, are not uncommon in certain strata of Devonian and
Silurian age (see p. 193). The fishes belonging to this sub-class may
be divided into two families--


                     FIRST FAMILY--PETROMYZONTIDÆ.

_Body eel-shaped, naked. Subject to a metamorphosis; in the perfect
stage with a suctorial mouth armed with teeth, simple or multicuspid,
horny, sitting on a soft papilla. Maxillary, mandibulary, lingual, and
suctorial teeth may be distinguished. Eyes present (in mature animals).
External nasal aperture in the middle of the upper side of the head.
The nasal duct terminates without perforating the palate. Seven
branchial sacs and apertures on each side behind the head; the inner
branchial ducts terminate in a separate common tube. Intestine with a
spiral valve. Eggs small. The larvæ without teeth, and with a single
continuous vertical fin._

“Lampreys” are found in the rivers and on the coasts of the temperate
regions of the northern and southern hemispheres. Their habits are but
incompletely known, but so much is certain that at least some of them
ascend rivers periodically, for the purpose of spawning, and that the
young pass several years in rivers, whilst they undergo a metamorphosis
(see p. 170). They feed on other fishes, to which they suck themselves
fast, scraping off the flesh with their teeth. Whilst thus engaged they
are carried about by their victim; Salmon have been captured in the
middle course of the Rhine with the Marine Lamprey attached to them.

  [Illustration: Fig. 315.--Mouth of Larva of Petromyzon
  branchialis.]

  [Illustration: Fig. 316.--Mouth of Petromyzon fluviatilis.
  _mx_, Maxillary tooth; _md_, Mandibulary tooth;
  _l_, Lingual tooth; _s_, Suctorial teeth.]

   PETROMYZON.--Dorsal fins two, the posterior continuous with the
   caudal. The maxillary dentition consists of two teeth placed
   close together, or of a transverse bicuspid ridge; lingual teeth
   serrated.

The Lampreys belonging to this genus are found in the northern
hemisphere only; the British species are the Sea-Lamprey (_P.
marinus_), exceeding a length of three feet, and not uncommon on the
European and North American coasts; the River-Lamprey or Lampern (_P.
fluviatilis_), ascending in large numbers the rivers of Europe, North
America, and Japan, and scarcely attaining a length of two feet; the
“Pride” or “Sand-Piper” or Small Lampern (_P. branchialis_), scarcely
twelve inches long, the larva of which has been long known under the
name of _Ammocoetes_.

_Ichthyomyzon_ from the western coasts of North America is said to have
a tricuspid maxillary tooth.

   MORDACIA.--Dorsal fins two, the posterior continuous with the
   caudal. The maxillary dentition consists of two triangular
   groups, each with three conical acute cusps; two pairs of
   serrated lingual teeth.

  [Illustration: Fig. 317.--Mouth of Mordacia mordax, closed and
  opened.]

A Lamprey _(M. mordax_) from the coasts of Chile and Tasmania. This
fish seems to be provided sometimes with a gular sac, like the
following.[47]

  [Illustration: Fig. 318.--Mordacia mordax.]

   GEOTRIA.--Dorsal fins two, the posterior separate from the
   caudal. Maxillary lamina with four sharp flat lobes; a pair of
   long pointed lingual teeth.

Two species, one from Chile and one from South Australia. They grow
to a length of two feet, and in some specimens the skin of the throat
is much expanded, forming a large pouch. Its physiological function
is not known. The cavity is in the subcutaneous cellular tissue, and
does not communicate with the buccal or branchial cavities. Probably
it is developed with age, and absent in young individuals. In all
the localities in which these Extra-european Lampreys are found,
_Ammocoetes_ forms occur, so that there is little doubt that they
undergo a similar metamorphosis as _P. branchialis_.


                       SECOND FAMILY--MYXINIDÆ.

_Body eel-shaped, naked. The single nasal aperture is above the
mouth, quite at the extremity of the head, which is provided with four
pairs of barbels. Mouth without lips. Nasal duct without cartilaginous
rings, penetrating the palate. One median tooth on the palate, and
two comb-like series of teeth on the tongue_ (see Fig. 101).
_Branchial apertures at a great distance from the head; the inner
branchial ducts lead into the œsophagus. A series of mucous sacs along
each side of the abdomen. Intestine without spiral valve. Eggs large,
with a horny case provided with threads for adhesion._

  [Illustration: Fig. 319.--Ovum of Myxine glutinosa, enlarged.]

The fishes of this family are known by the names of “Hag-Fish,”
“Glutinous Hag,” or “Borer;” they are marine fishes with a similar
distribution as the Gadidæ, being most plentiful in the higher
latitudes of the temperate zones of the northern and southern
hemispheres. They are frequently found buried in the abdominal cavity
of other fishes, especially Gadoids, into which they penetrate to feed
on their flesh. They secrete a thick glutinous slime in incredible
quantities, and are therefore considered by fishermen a great nuisance,
seriously damaging the fisheries and interfering with the fishing in
localities where they abound. _Myxine_ descends to a depth of
345 fathoms, and is generally met with in the Norwegian Fjords at 70
fathoms, sometimes in great abundance.

   MYXINE.--One external branchial aperture only on each side of
   the abdomen, leading by six ducts to six branchial sacs.

Three species from the North Atlantic, Japan, and Magelhæn’s Straits.

  [Illustration: Fig. 320.--Myxine australis. A, Lower aspect
  of head; _a_, Nasal aperture; _b_, Mouth; _g_,
  Branchial aperture; _v_, Vent.]

   BDELLOSTOMA.--Six or more external branchial apertures on each
   side, each leading by a separate duct to a branchial sac.

Two species from the South Pacific.


                    FOURTH SUB-CLASS--LEPTOCARDII.


_Skeleton membrano-cartilaginous and notochordal, ribless. No brain.
Pulsating sinuses in place of a heart. Blood colourless. Respiratory
cavity confluent with the abdominal cavity; branchial clefts in great
number, the water being expelled by an opening in front of the vent.
Jaws none._

This sub-class is represented by a single family (_Cirrostomi_)
and by a single genus (_Branchiostoma_);[48] it is the lowest in
the scale of fishes, and lacks so many characteristics, not only of
this class, but of the vertebrata generally, that Hæckel, with good
reason, separates it into a separate class, that of _Acrania_. The
various parts of its organisation have been duly noticed in the first
part of this work.

The “Lancelet” (_Branchiostoma lanceolatum_, see Fig. 28, p. 63),
seems to be almost cosmopolitan within the temperate and tropical
zones. Its small size, its transparency, and the rapidity with which it
is able to bury itself in the sand, are the causes why it escapes so
readily observation, even at localities where it is known to be common.
Shallow, sandy parts of the coasts seem to be the places on which it
may be looked for. It has been found on many localities of the British,
and generally European coasts, in North America, the West Indies,
Brazil, Peru, Tasmania, Australia, and Borneo. It rarely exceeds
a length of three inches. A smaller species, in which the dorsal
fringe is distinctly higher and rayed, and in which the caudal fringe
is absent, has been described under the name of _Epigionichthys
pulchellus_; it was found in Moreton Bay.




                               APPENDIX.

           DIRECTIONS FOR COLLECTING AND PRESERVING FISHES.


Whenever practicable fishes ought to be preserved in spirits.

To insure success in preserving specimens the best and strongest
spirits should be procured, which, if necessary, can be reduced to
the strength required during the journey with water or weaker spirit.
Travellers frequently have great difficulties in procuring spirits
during their journey, and therefore it is advisable, especially during
sea voyages, that the traveller should take a sufficient quantity
with him. Pure spirits of wine is best. Methylated spirits may be
recommended on account of their cheapness; however, specimens do not
keep equally well in this fluid, and very valuable objects, or such as
are destined for minute anatomical examination, should always be kept
in pure spirits of wine. If the collector has exhausted his supply of
spirits he may use arrack, cognac, or rum, provided that the fluids
contain a sufficient quantity of alcohol. Generally speaking, spirits
which, without being previously heated, can be ignited by a match or
taper, may be used for the purposes of conservation. The best method
to test the strength of the spirits is the use of a hydrometer. It
is immersed in the fluid to be measured, and the deeper it sinks the
stronger is the spirit. On its scale the number 0 signifies what is
called proof spirit, the lowest degree of strength which can be used
for the conservation of fish for any length of time. Spirits, in which
specimens are packed permanently, should be from 40 to 60 above proof.
If the hydrometers are made of glass they are easily broken, and
therefore the traveller had better provide himself with three or four
of them, their cost being very trifling. Further, the collector will
find a small distilling apparatus very useful. By its means he is able
not only to distil weak and deteriorated spirits or any other fluid
containing alcohol, but also, in case of necessity, to prepare a small
quantity of drinkable spirits.

Of collecting vessels we mention first those which the collector
requires for daily use. Most convenient are four-sided boxes made of
zinc, 18 in. high, 12 in. broad, and 5 in. wide. They have a round
opening at the top of 4 in. diameter, which can be closed by a strong
cover of zinc of 5 in. diameter, the cover being screwed into a raised
rim round the opening. In order to render the cover air-tight, an
indiarubber ring is fixed below its margin. Each of these zinc boxes
fits into a wooden case, the lid of which is provided with hinges and
fastenings, and which on each side has a handle of leather or rope, so
that the box can be easily shifted from one place to another. These
boxes are in fact made from the pattern of the ammunition cases used
in the British army, and extremely convenient, because a pair can be
easily carried strapped over the shoulders of a man or across the
back of a mule. The collector requires at least two, still better
four or six, of these boxes. All those specimens which are received
during the day are deposited in them, in order to allow them to be
thoroughly penetrated by the spirit, which must be renewed from time
to time. They remain there for some time under the supervision of the
collector, and are left in these boxes until they are hardened and
fit for final packing. Of course, other more simple vessels can be
used and substituted for the collecting boxes. For instance, common
earthenware vessels, closed by a cork or an indiarubber covering,
provided they have a wide mouth at the top, which can be closed so
that the spirit does not evaporate, and which permits of the specimens
being inspected at any moment without trouble. Vessels in which the
objects are permanently packed for the home journey are zinc boxes of
various sizes, closely fitting into wooden cases. Too large a size
should be avoided, because the objects themselves may suffer from the
superimposed weight, and the risk of injury to the case increases with
its size. It should hold no more than 18 cubic feet at most, and what,
in accordance with the size of the specimens, has to be added in length
should be deducted in depth or breadth. The most convenient cases,
but not sufficient for all specimens, are boxes 2 feet in length, 1½
foot broad, and 1 foot deep. The traveller may provide himself with
such cases ready made, packing in them other articles which he wants
during his journey; or he may find it more convenient to take with him
only the zinc plates cut to the several sizes, and join them into boxes
when they are actually required. The requisite wooden cases can be
procured without much difficulty almost everywhere. No collector should
be without the apparatus and materials for soldering, and he should be
well acquainted with their use. Also a pair of scissors to cut the zinc
plates are useful.

Wooden casks are not suitable for the packing of specimens preserved
in spirits, at least not in tropical climates. They should be used in
cases of necessity only, or for packing of the largest examples, or for
objects preserved in salt or brine.

Very small and delicate specimens should never be packed together with
larger ones, but separately, in small bottles.

_Mode of preserving._--All fishes, with the exception of very
large ones (broad kinds exceeding 3–4 feet in length; eel-like kinds
more than 6 feet long), should be preserved in spirits. A deep cut
should be made in the abdomen between the pectoral fins, another in
front of the vent, and one or two more, according to the length of
the fish, along the middle line of the abdomen. These cuts are made
partly to remove the fluid and easily decomposing contents of the
intestinal tract, partly to allow the spirit quickly to penetrate into
the interior. In large fleshy fishes several deep incisions should
be made with the scalpel into the thickest parts of the dorsal and
caudal muscles, to give ready entrance to the spirits. The specimens
are then placed in one of the provisional boxes, in order to extract,
by means of the spirit, the water of which fishes contain a large
quantity. After a few days (in hot climates after 24 or 48 hours) the
specimens are transferred into a second box with stronger spirits, and
left therein for several days. A similar third and, in hot climates
sometimes a fourth, transfer is necessary. This depends entirely on
the condition of the specimens. If, after ten or fourteen days of
such treatment the specimens are firm and in good condition, they may
be left in the spirits last used until they are finally packed. But
if they should be soft, very flexible, and discharge a discoloured
bloody mucus, they must be put back in spirits at least 20° over proof.
Specimens showing distinct signs of decomposition should be thrown
away, as they imperil all other specimens in the same vessel. Neither
should any specimen in which decomposition has commenced when found, be
received for the collecting boxes, unless it be of a very rare species,
when the attempt may be made to preserve it separately in the strongest
spirits available. The fresher the specimens to be preserved are, the
better is the chance of keeping them in a perfect condition. Specimens
which have lost their scales, or are otherwise much injured, should not
be kept. Herring-like fishes, and others with deciduous scales, are
better wrapped in thin paper or linen before being placed in spirits.

The spirits used during this all-important process of preservation
loses, of course, gradually in strength. As long as it keeps 10° under
proof it may still be used for the first stage of preservation, but
weaker spirits should be re-distilled; or, if the collector cannot do
this, it should be at least filtered through powdered charcoal before
it is mixed with stronger spirits. Many collectors are satisfied with
removing the thick sediment collected at the bottom of the vessel,
and use their spirits over and over again without removing from it by
filtration the decomposing matter with which it has been impregnated,
and which entirely neutralises the preserving property of the spirits.
The result is generally the loss of the collection on its journey
home. The collector can easily detect the vitiated character of his
spirits by its bad smell. He must frequently examine his specimens; and
attention to the rules given, with a little practice and perseverance,
after the possible failure of the first trial, will soon insure to
him the safety of his collected treasures. The trouble of collecting
specimens in spirits is infinitely less than that of preserving skins
or dry specimens of any kind.

When a sufficient number of well-preserved examples have been brought
together, they should be sent home by the earliest opportunity. Each
specimen should be wrapped separately in a piece of linen, or at least
soft paper; the specimens are then packed as close as herrings in the
zinc case, so that no free space is left either at the top or on the
sides. When the case is full, the lid is soldered on, with a round
hole about half an inch in diameter near one of the corners. This hole
is left in order to pour the spirit through it into the case. Care is
taken to drive out the air which may remain between the specimens,
and to surround them completely with spirits, until the case is quite
full. Finally, the hole is closed by a small square lid of tin being
soldered over it. In order to see whether the case keeps in the spirit
perfectly, it is turned upside down and left over night. When all is
found to be securely fastened, the zinc case is placed into the wooden
box and ready for transport.

Now and then it happens in tropical climates that collectors are unable
to keep fishes from decomposition even in the strongest spirits without
being able to detect the cause. In such cases a remedy will be found in
mixing a small quantity of arsenic or sublimate with the spirits; but
the collector ought to inform his correspondent, or the recipient of
the collection, of this admixture having been made.

In former times fishes of every kind, even those of small size, were
preserved dry as flat skins or stuffed. Specimens thus prepared admit
of a very superficial examination only, and therefore this method of
conservation has been abandoned in all larger museums, and should be
employed exceptionally only, for instance on long voyages overland,
during which, owing to the difficulty of transport, neither spirits
nor vessels can be carried. To make up as much as possible for the
imperfection of such specimens, the collector ought to sketch the
fish before it is skinned, and to colour the sketch if the species
is ornamented with colours likely to disappear in the dry example.
Collectors who have the requisite time and skill, ought to accompany
their collections with drawings coloured from the living fishes; but
at the same time it must be remembered that, valuable as such drawings
are if accompanied by the originals from which they were made, they can
never replace the latter, and possess a subordinate scientific value
only.

Very large fishes can be preserved as skins only; and collectors are
strongly recommended to prepare in this manner the largest examples
obtainable, although it will entail some trouble and expense. So
very few large examples are exhibited in museums, the majority of the
species being known from the young stage only, that the collector will
find himself amply recompensed by attending to these desiderata.

Scaly fishes are skinned thus: with a strong pair of scissors an
incision is made along the median line of the abdomen from the foremost
part of the throat, passing on one side of the base of the ventral
and anal fins, to the root of the caudal fin, the cut being continued
upwards to the back of the tail close to the base of the caudal. The
skin of one side of the fish is then severed with the scalpel from the
underlying muscles to the median line of the back; the bones which
support the dorsal and caudal are cut through, so that these fins
remain attached to the skin. The removal of the skin of the opposite
side is easy. More difficult is the preparation of the head and
scapulary region; the two halves of the scapular arch which have been
severed from each other by the first incision are pressed towards the
right and left, and the spine is severed behind the head, so that now
only the head and shoulder bones remain attached to the skin. These
parts have to be cleaned from the inside, all soft parts, the branchial
and hyoid apparatus, and all smaller bones, being cut away with the
scissors or scraped off with the scalpel. In many fishes, which
are provided with a characteristic dental apparatus in the pharynx
(Labroids, Cyprinoids), the pharyngeal bones ought to be preserved,
and tied with a thread to the specimen. The skin being now prepared so
far, its entire inner surface as well as the inner side of the head are
rubbed with arsenical soap; cotton-wool, or some other soft material is
inserted into any cavities or hollows, and finally a thin layer of the
same material is placed between the two flaps of the skin. The specimen
is then dried under a slight weight to keep it from shrinking.

The scales of some fishes, as for instance of many kinds of herrings,
are so delicate and deciduous that the mere handling causes them to rub
off easily. Such fishes may be covered with thin paper (tissue-paper
is the best), which is allowed to dry on them before skinning. There
is no need for removing the paper before the specimen has reached its
destination.

Scaleless Fishes, as Siluroids and Sturgeons, are skinned in the same
manner, but the skin can be rolled up over the head; such skins can
also be preserved in spirits, in which case the traveller may save to
himself the trouble of cleaning the head.

Some Sharks are known to attain to a length of 30 feet, and some Rays
to a width of 20 feet. The preservation of such gigantic specimens is
much to be recommended, and although the difficulties of preserving
fishes increase with their size, the operation is facilitated, because
the skins of all Sharks and Rays can easily be preserved in salt and
strong brine. Sharks are skinned much in the same way as ordinary
fishes. In Rays an incision is made not only from the snout to the end
of the fleshy part of the tail, but also a second across the widest
part of the body. When the skin is removed from the fish, it is placed
into a cask with strong brine mixed with alum, the head occupying the
upper part of the cask; this is necessary, because this part is most
likely to show signs of decomposition, and therefore most requires
supervision. When the preserving fluid has become decidedly weaker from
the extracted blood and water, it is thrown away and replaced by fresh
brine. After a week’s or fortnight’s soaking the skin is taken out of
the cask to allow the fluid to drain off; its inner side is covered
with a thin layer of salt, and after being rolled up (the head being
inside) it is packed in a cask, the bottom of which is covered with
salt; all the interstices and the top are likewise filled with salt.
The cask must be perfectly water-tight.

Of all larger examples of which the skin is prepared, the measurements
should be taken before skinning so as to guide the taxidermist in
stuffing and mounting the specimens.

Skeletons of large osseous fishes are as valuable as their skins. To
preserve them it is only necessary to remove the soft parts of the
abdominal cavity and the larger masses of muscle, the bones being left
in their natural continuity. The remaining flesh is allowed to dry on
the bones, and can be removed by proper maceration at home. The fins
ought to be as carefully attended to as in a skin, and of scaly fishes
so much of the external skin ought to be preserved as is necessary
for the determination of the species, as otherwise it is generally
impossible to determine more than the genus.

A few remarks may be added as regards those Faunæ, which promise most
results to the explorer, with some hints as to desirable information on
the life and economic value of fishes.

It is surprising to find how small the number is of the freshwater
faunæ which may be regarded as well explored; the rivers of Central
Europe, the Lower Nile, the lower and middle course of the Ganges,
and the lower part of the Amazons are almost the only fresh waters
in which collections made without discrimination would not reward
the naturalist. The oceanic areas are much better known; yet almost
everywhere novel forms can be discovered and new observations
made. Most promising and partly quite unknown are the following
districts:--the Arctic Ocean, all coasts south of 38° lat. S., the
Cape of Good Hope, the Persian Gulf, the coasts of Australia (with the
exception of Tasmania, New South Wales, and New Zealand), many of the
little-visited groups of Pacific islands, the coasts of north-eastern
Asia north of 35° lat. N., and the western coasts of North and South
America.

No opportunity should be lost to obtain _pelagic_ forms,
especially the young larva-like stages of development abounding on the
surface of the open ocean. They can be obtained without difficulty by
means of a small narrow meshed net dragged behind the ship. The sac
of the net is about 3 feet deep, and fastened to a strong brass-ring
2 or 2½ feet in diameter. The net is suspended by three lines passing
into the strong main line. It can only be used when the vessel moves
very slowly, its speed not exceeding three knots an hour, or when a
current passes the ship whilst at anchor. To keep the net in a vertical
position the ring can be weighted at one point of its circumference;
and by using heavier weights two or three drag-nets can be used
simultaneously at different depths. This kind of fishing should be
tried at night as well as day, as many fishes come to the surface only
after sunset. The net must not be left long in the water, from 5 to 20
minutes only, as delicate objects would be sure to be destroyed by the
force of the water passing through the meshes.

Objects found floating on the surface, as wood, baskets, seaweed,
etc., deserve the attention of the travellers, as they are generally
surrounded by small fishes or other marine animals.

It is of the greatest importance to note the longitude and latitude at
which the objects were collected in the open ocean.

Fishing in great depths by means of the dredge, can be practised
only from vessels specially fitted out for the purpose; and the
success which attended the “Challenger,” and North American Deep-sea
explorations, has developed Deep-sea fishing into such a speciality
that the requisite information can be gathered better by consulting the
reports of those expeditions than from a general account, such as could
be given in the present work.

Fishes offer an extraordinary variety with regard to their habits,
growth, etc., so that it is impossible to enumerate in detail the
points of interest to which the travellers should pay particular
attention. However, the following hints may be useful.

Above all, detailed accounts are desirable of all fishes forming
important articles of trade, or capable of becoming more generally
useful than they are at present. Therefore, deserving of special
attention are the Sturgeons, Gadoids, Thyrsites and Chilodactylus,
Salmonoids, Clupeoids. Wherever these fishes are found in sufficient
abundance, new sources may be opened to trade.

Exact observations should be made on the fishes the flesh of which is
poisonous either constantly or at certain times and certain localities;
the cause of the poisonous qualities as well as the nature of the
poison should be ascertained. Likewise the poison of fishes provided
with special poison-organs requires to be experimentally examined,
especially with regard to its effects on other fishes and animals
generally.

All observations directed to sex, mode of propagation, and development,
will have special interest: thus those relating to secondary sexual
characters, hermaphroditism, numeric proportion of the sexes, time of
spawning and migration, mode of spawning, construction of nests, care
of progeny, change of form during growth, etc.

If the collector is unable to preserve the largest individuals of a
species that may come under his observation he should note at least
their measurements. There are but few species of fishes of which the
limit of growth is known.

The history of Parasitic Fishes is almost unknown, and any
observations with regard to their relation to their host as well as to
their early life will prove to be valuable; nothing is known of the
propagation of fishes even so common as Echeneis and Fierasfer, much
less of the parasitic Freshwater Siluroids.

The temperature of the blood of the larger freshwater and marine
species should be exactly measured.

Many pelagic and deep-sea fishes are provided with peculiar small
round organs of a mother-of-pearl colour, distributed in series along
the side of the body, especially along the abdomen. Some zoologists
consider these organs as accessory eyes, others (and it appears to
us with better reason) as luminous organs. They deserve an accurate
microscopic examination made on fresh specimens; and their function
should be ascertained from observation of the living fishes, especially
also with regard to the question, whether or not the luminosity (if
such be their function) is subject to the will of the fish.

  [Illustration: Fig. 321.--Scopelus boops, a pelagic fish, with
  luminous organs.]




                                INDEX.


    Abdominal Cavity, 123

    Abdominal fins, 42

    Abramis, 602

    Abrostomus, 596

    Acanthaphritis, 466

    Acanthias, 331

    Acanthicus, 576

    Acanthobrama, 604

    Acanthoclinus, 498

    Acanthodes, 355

    Acanthodini, 355

    Acantholabrus, 528

    Acanthonus, 547

    Acanthophthalmus, 606

    Acanthopsis, 606

    Acanthopterygiau, 41

    Acanthopterygii, 374

    Acanthorhodeus, 601

    Acanthurus, 438, 439

    Acanus, 421

    Acara, 536

    Acclimatisation, 185

    Acentronura, 683

    Acerina, 378

    Acestra, 579

    Achilognathus, 601

    Acipenser, 361

    Acipenseridæ, 360

    Acrochilus, 601

    Acrochordonichthys, 567

    Acrodus, 330

    Acrogaster, 421

    Acrognathus, 631

    Acrolepis, 370

    Acronuridæ, 438

    Acronurus, 439

    Acropoma, 395

    Acyprinoid division, 218

    Adipose eyelid, 113

    Adipose fin, 42

    Aegæonichthys, 476

    Aellopos, 325

    Aelurichthys, 569

    Aesopia, 558

    Aëtobatis, 345

    African region, 227

    Agassiz, 20, 31, 32

    Ageniosus, 572

    Agnus, 463

    Agoniates, 610

    Agonostoma, 504

    Agonus, 480

    Agrammus, 491

    Agriopus, 416

    Ailia, 566

    Aipichthys, 441

    Air-bladder, 142

    Akysis, 567

    Albacore, 458

    Albinism, 183

    Alborella, 604

    Albula, 660

    Albulichthys, 596

    Alburnus, 603

    Alepocephalus, 664

    Alestes, 608

    Ale-wife, 659

    Alisphenoid, 56, 88

    Allice Shad, 659

    Alopecias, 322

    Ambassis, 393

    Amblyopsis, 618

    Amblyopus, 489

    Amblypharyngodon, 598

    Amblypterus, 370

    Amblyrhynchichthys, 596

    Amia, 372

    Amioidei, 370

    Amiurus, 567

    Ammocoetes, 693

    Ammodytes, 550

    Ammopleurops, 559

    Ammotretis, 557

    Amphioxus, 696

    Amphipnous, 668

    Amphiprion, 525

    Amphisile, 509

    Amphistium, 442

    Anabas, 516

    Anableps, 617

    Anacanthini, 537

    Anacanthus, 684

    Anacyrtus, 611

    Anal fin, 40, 42

    Anampses, 529

    Anapterus, 582

    Anarrhichas, 492

    Anastomus, 608

    Anchovy, 656

    Ancistrodon, 319

    Ancylodon, 430

    Anema, 463

    Anenchelum, 433

    Angel-fish, 334

    Angler, 470

    Anguilla, 671

    Angular bone, 54, 91

    Anomalops, 449

    Anoplogaster, 422

    Antarctic ocean, 289

    Antennarius, 473

    Anthias, 380

    Anticitharus, 556

    Antigonia, 449

    Aphanopus, 434

    Aphareus, 390

    Aphoristia, 559

    Aphredoderus, 396

    Aphritis, 466

    Aphyocharax, 610

    Aphyocypris, 598

    Aphyonus, 548

    Apionichthys, 559

    Apistus, 415

    Aploactis, 417

    Apocryptes, 487

    Apodichthys, 496

    Apogon, 394

    Apophyses, 51

    Appendices pyloricæ, 131

    Aprion, 397

    Apsilus, 397

    Apua, 606

    Arapaima, 654

    Archæus, 442

    Archipterygium, 74

    Arctic ocean, 261

    Arctic zone, 241

    Argentina, 650

    Arges, 575

    Argyropelecus, 628

    Argyriosus, 443

    Aristotle, 1

    Arius, 569

    Arnoglossus, 556

    Arrhamphus, 621

    Arripis, 393

    Artedi, 9

    Artedius, 480

    Arthropterus, 342

    Articulary bone, 54, 90

    Articulated rays, 40

    Asima, 405

    Aspidoparia, 602

    Aspidophoroides, 480

    Aspidorhynchidæ, 369

    Aspius, 603

    Aspredo, 580

    Aspro, 379

    Astracanthus, 314

    Astrape, 340

    Astrolepis, 354

    Astronesthes, 629

    Astrophysus, 572

    Astroplebus, 575

    Astroptychius, 314

    Ateleopus, 553

    Atherina, 500

    Atherinichthys, 501

    Atlantic, tropical, 278

    Atlantic, northern, 262

    Atopochilus, 570

    Atopomycterus, 689

    Atypichthys, 402

    Auchenaspis, 354

    Auchenipterus, 572

    Auchenoglanis, 569

    Aulacocephalus, 383

    Aulolepis, 631

    Aulichthys, 508

    Auliscops, 507, 508

    Aulopus, 587

    Aulopyge, 596

    Aulorhynchus, 508

    Aulostoma, 507, 508

    Ausonia, 455

    Ausonius, 3

    Autochthont, 214

    Autostylic skull, 71

    Auxis, 459

    Avola, 604


    Badis, 418

    Baer, 32

    Bagarius, 570

    Bagrichthys, 567

    Bagroides, 567

    Bagropsis, 568

    Bagrus, 567

    Baird, 29

    Bakker, 32

    Balfour, 32, 33

    Balistes, 684

    Ballan Wrasse, 527

    Band-fish, 490

    Barbel, 594

    Barbels, 37

    Barbichthys, 596

    Barbus, 594

    Barilius, 602

    Barracuda, 437, 499

    Barramunda, 357

    Barynotus, 596

    Basibranchial, 58

    Basihyal, 58

    Basioccipital, 56, 87

    Basisphenoid, 56, 57, 89

    Basking shark, 322

    Bass, 376

    Bastard Dorey, 388

    Bathydraco, 465

    Bathygadus, 552

    Bathylagus, 650

    Bathynectes, 547

    Bathyophis, 629

    Bathypterois, 583

    Bathysaurus, 582

    Bathythrissa, 668

    Bathytroctes, 664

    Batoidei, 335

    Batrachocephalus, 570

    Batrachus, 467

    Bayad, 567

    Bdellostoma, 695

    Becker, 408

    Bellows-fish, 509

    Belodontichthys, 566

    Belon, 3

    Belone, 620

    Belonesox, 617

    Belonostomus, 369

    Bembras, 480

    Benedenius, 370

    Benthophilus, 489

    Berycidæ, 420

    Berycopsis, 421

    Beryx, 422

    Betta, 518

    Bib, 541

    Bichir, 364

    Bitterling, 601

    Black Bass, 393

    Black-fish, 452, 527

    Black Head, 596

    Black Horses, 589

    Black Sea-bream, 406

    Blanchard, 28

    Bleak, 604

    Bleeker, 30

    Bleekeria, 550

    Blenniidæ, 492

    Blenniops, 496

    Blennius, 493

    Blennodesmus, 538

    Blennophis, 498

    Blenny, 492

    Blepsias, 480

    Blind fish, 618

    Bloch, 13

    Blood-corpuscles, 150

    Blue-fish, 447

    Boar-fish, 388, 449

    Bocage, 28

    Bocourt, 31

    Bola, 602

    Boleophthalmus, 487

    Boleosoma, 379

    Bolty, 535

    Bombay-duck, 584

    Bonaparte, 28

    Bonelli, 7

    Bonito, 458

    Bony Pike, 367

    Borer, 694

    Botia, 605

    Bovichthys, 465

    Bow-fin, 372

    Box, 406

    Brachionichthys, 474

    Brachymystax, 646

    Brachypleura, 556

    Brackish water fishes, 250

    Brain, 97

    Brama, 454

    Branched rays, 40

    Branchiæ, 136

    Branchial arches, 58

    Branchiostegals, 39, 58, 91

    Branchiostoma, 696

    Bream, 602

    Bregmaceros, 545

    Brill, 555

    British district, 263

    Brontes, 575

    Brook-trout, 646

    Brosmius, 546

    Brotula, 546

    Brotulophis, 549

    Brünnich, 13

    Brycon, 610

    Bryconæthiops, 610

    Bryconops, 610

    Bryttus, 396

    Buccal cavity, 123

    Bulbus aortæ, 152

    Bull-head, 476

    Bull-trout, 644

    Bulti, 535

    Buffaloe, 589

    Bummaloh, 584

    Bungia, 596

    Bunocephalichthys, 580

    Bunocephalus, 580

    Bunocottus, 480

    Burbot, 544

    Bursa entiana, 128

    Burton Skate, 341

    Butter-fish, 496, 533

    Bynni, 594

    Bythites, 549


    Cachius, 604

    Cænotropus, 607

    Cæsio, 390

    Calamoichthys, 364

    Californian district, 271

    Calamostoma, 680

    Callanthias, 381

    Callichrous, 566

    Callichthys, 575

    Callionymus, 489

    Callipteryx, 462

    Callomystax, 573

    Callophysus, 569

    Callorhynchus, 350

    Callyodon, 532

    Camper, 16

    Campostoma, 596

    Cantharina, 405

    Cantharus, 405

    Cantor, 30

    Capelin, 647

    Capello, 28

    Cape of Good Hope, 283

    Capitodus, 405

    Capoëta, 593

    Capros, 449

    Carangidæ, 440

    Carangopsis, 442

    Caranx, 442

    Carapus, 667

    Carassius, 591

    Carboniferous fishes, 196

    Carcharias, 316

    Carchariidæ, 316

    Carcharodon, 320

    Carcharopsis, 319

    Cardlike teeth, 126

    Caribe, 613

    Carmoot, 563

    Carp, 589

    Carpals, 59

    Carpiodes, 589

    Cartilage-bones, 87

    Castelnau, 31

    Cataphracti, 480

    Cat-fishes, 568

    Catla, 592

    Catopra, 418

    Catoprion, 613

    Catostomus, 589

    Caturidæ, 371

    Caudal fin, 40

    Cebidichthys, 498

    Central American district, 279

    Centrarchus, 396

    Centridermichthys, 477

    Centrina, 331

    Centriscus, 509

    Centrolabrus, 528

    Ceutrolepis, 370

    Centrolophus, 452

    Centromochlus, 572

    Centronotus, 496

    Centrophorus, 331

    Centropogon, 417

    Centropomus, 379

    Ceutropristis, 380

    Centroscyllium, 332

    Centrum, 51

    Cephalacanthus, 482

    Cephalaspis, 353

    Cephaloptera, 347

    Cephenoplosus, 368

    Cepola, 490

    Ceratias, 472

    Ceratichthys, 596

    Ceratobranchial, 58

    Ceratodus, 357

    Ceratohyal, 58

    Ceratoptera, 347

    Cerebellum, 97

    Cestracion, 330

    Cestraciontidæ, 328

    Cetengraulis, 656

    Cetopsis, 572

    Chaca, 564

    Chad, 408

    Chænichthys, 466

    Chætobranchus, 537

    Chætodon, 398

    Chætopterus, 390

    Chætostomus, 576

    Chalceus, 610

    Chalcinopsis, 610

    Chalcinus, 610

    Champsodon, 464

    Channa, 513

    Chanodichthys, 604

    Chanos, 662

    Characinidæ, 606

    Characodon, 615

    Charr, 645

    Chasmodes, 494

    Chatoëssus, 657

    Chauliodus, 628

    Chaunax, 474

    Cheilio, 530

    Chela, 604

    Chelmo, 399

    Chiasmodus, 546

    Chilian district, 288

    Chilinus, 528

    Chilobranchus, 669

    Chilodactylus, 411

    Chilodipterus, 395

    Chilomycterus, 689

    Chilorhinus, 674

    Chiloscyllium, 326, 327

    Chimæra, 349

    Chimæridæ, 348

    Chimarrhichthys, 466

    Chiracanthus, 355

    Chirocentrites, 656

    Chirocentrodon, 660

    Chirocentrus, 663

    Chirodon, 609

    Chirodus, 370

    Chirolepis, 370

    Chironemus, 411

    Chirus, 491

    Chlorophthalmus, 587

    Chœrops, 530

    Chologaster, 618

    Chomatodus, 329

    Chondropterygii, 313

    Chondrostei, 360

    Chondrosteus, 363

    Chondrostoma, 600

    Chorda dorsalis, 63

    Chorinemus, 446

    Chorismodactylus, 417

    Chorisochismus, 512

    Chromatophors, 183

    Chromides, 534

    Chromis, 535

    Chrysichthys, 567

    Chrysophrys, 409

    Chub, 596, 599, 600

    Cichla, 536

    Cichlops, 466

    Circulation, organs of, 150

    Cirrhilabrus, 530

    Cirrhina, 596

    Cirrhites, 411

    Cirrhitidæ, 410

    Cirrostomi, 696

    Citharichthys, 556

    Citharinus, 607

    Citharus, 556

    Cladacanthus, 314

    Cladodus, 328

    Clarias, 563

    Clarotes, 567

    Claspers, 167

    Clavicula, 59, 92

    Clepticus, 530

    Climbing Perch, 516

    Clinus, 495

    Cloudy Bay cod, 549

    Clupea, 658

    Clupeichthys, 660

    Clupeoides, 660

    Cnidoglanis, 564

    Coal-fish, 541

    Cobitis, 605

    Coccia, 628

    Coccosteus, 351

    Cochlognathus, 596

    Cochliodus, 329

    Cock-and-hen Paddle, 484

    Cod-fishes, 539

    Cœcal stomach, 130

    Coelacanthidæ, 365

    Coelodus, 367

    Coelogaster, 656

    Coelonotus, 681

    Coelorhynchus, 433

    Coffer-fish, 686

    Coilia, 657

    Collichthys, 430

    Commerson, 13

    Conger, 673

    Congrogadina, 550

    Congromuræna, 674

    Conodon, 386

    Conodonts, 193

    Conodus, 368

    Conorhynchus, 569

    Conus arteriosus, 151

    Cook, 527

    Copidoglanis, 564

    Coracoid, 59, 92

    Coral-fishes, 397, 525

    Corax, 317

    Coregonus, 647

    Coridodax, 533

    Coris, 530

    Cork-wing, 527

    Cornide, 13

    Corpora quadrigemina, 103

    Corpora restiformia, 99

    Corpora striata, 100

    Corvina, 430

    Corvo, 429

    Corynopoma, 607

    Coryphæna, 452

    Coryphænoides, 552

    Cosmolepis, 370

    Cosmoptychius, 370

    Cossyphus, 528

    Costa, 28

    Cottoperca, 466

    Cottus, 476

    Cotylis, 512

    Couch, 27

    Couchia, 544

    Craig-fluke, 557

    Creagrutus, 610

    Cremnobates, 495

    Crenicichla, 537

    Crenidens, 406

    Crenilabrus, 527

    Crenuchus, 612

    Crepidogaster, 513

    Cretaceous fishes, 199

    Cricacanthus, 314

    Cristiceps, 495

    Crossochilus, 596

    Crossognathus, 656

    Crossorhinus, 328

    Crossostoma, 604

    Crucian carp, 591

    Crura cerebri, 98

    Cryptacanthodes, 496

    Cryptopterus, 566

    Ctenododipteridæ, 359

    Ctenodus, 359

    Ctenoid scales, 46

    Ctenolabrus, 527

    Ctenopharyngodon, 601

    Ctenopoma, 516

    Ctenoptychius, 329

    Cubiceps, 456

    Culter, 604

    Curimatus, 607

    Cut-lips, 596

    Cuvier, 17

    Cyathaspis, 354

    Cybium, 459

    Cyclobatis, 340

    Cycloid scales, 46

    Cyclopoma, 375

    Cyclopterus, 484

    Cycloptychius, 370

    Cyclostomata, 691

    Cyclurus, 588

    Cyema, 670

    Cymolutes, 530

    Cynodon, 611

    Cynoglossus, 558

    Cynolebias, 615

    Cyprinidæ, 587

    Cyprinion, 598

    Cyprinodon, 614

    Cyprinoid division, 217

    Cyprinus, 589

    Cyttidæ, 450

    Cyttus, 451


    Dab, 557

    Dace, 599, 600

    Dactylopterus, 481

    Dactyloscopus, 498

    Dangila, 596

    Danio, 602

    Dascyllus, 525

    Datnioides, 397

    Daurade, 409

    Day, 30

    Deal-fish, 522

    Decodon, 530

    Deep-sea fishes, 296

    Dekay, 29

    Dendrodus, 365

    Dentary, 54, 91

    Dentex, 389

    Dercetis, 666

    Dermal spines, 53

    Dermoskeleton, 85

    Devil-fishes, 344

    Devonian fishes, 193, 194

    Diagramma, 386

    Diana, 455

    Dibranchus, 475

    Dicerobatis, 347

    Dicotylichthys, 689

    Dicrotus, 437

    Dictyosoma, 498

    Didymaspis, 354

    Digestion, organs of, 121

    Dimeracanthus, 314

    Dinematichthys, 549

    Dinichthys, 352

    Diodon, 689

    Dioecious, 157

    Diplocrepis, 513

    Diplomystax, 569

    Diplophos, 629

    Diploprion, 383

    Diplopterus, 365

    Dipnoi, 355

    Dipterodon, 406

    Dipterus, 359

    Diptychus, 595

    Diretmus, 449

    Discoboli, 483

    Discognathus, 593

    Discopyge, 340

    Distichodus, 612

    Ditrema, 534

    Dog-fishes, 325, 619

    Doliichthys, 487

    Dolphins, 453

    Domesticated fishes, 185

    Domine, 436

    Donovan, 17

    Doras, 572

    Doratonotus, 530

    Dorsal fin, 40

    Dorsch, 540

    Dory, 450

    Doryichthys, 681

    Doydixodon, 406

    Dragonet, 489

    Drepane, 402

    Drepanephorus, 331

    Drum, 427

    Ductor, 442

    Ductus choledochus, 133

    Ductus cysticus, 133

    Duhamel, 13

    Dules, 384

    Duméril, 33

    Dussumieria, 662

    Duverney, 7

    Duymæria, 530


    Eagle-Rays, 344

    Ear, 116

    Echeneis, 460

    Echinorhinus, 333

    Echiostoma, 629

    Ectopterygoid, 90

    Edaphodon, 349

    Eel, 671

    Eel-pout, 544

    Egertonia, 526

    Elacate, 460

    Elasmodus, 349

    Elasmognathus, 349

    Electric Eel, 667

    Electric organs, 94

    Electric Rays, 339

    Electric Sheath-fish, 574

    Eleotris, 488

    Elonichthys, 370

    Elopichthys, 604

    Elops, 661

    Embiotocidæ, 533

    Encheliophis, 549

    Enchelycore, 677

    Enchodus, 433

    Endoskeleton, 85

    Engraulis, 656

    Enneodon, 687

    Enoplosus, 380

    Entopterygoid, 55, 90

    Epalzeorhynchus, 596

    Ephippus, 402

    Epibranchial, 59

    Epibulus, 528

    Epicoracoid, 59

    Epididymis, 167

    Epigionichthys, 696

    Epihyal, 58

    Epinnula, 436

    Epioticum, 88

    Epiphysis, 98

    Epitympanic, 55

    Equatorial zone, 218, 272

    Eques, 431

    Equula, 449

    Eremophilus, 581

    Erethistes, 580

    Ericymba, 596

    Erythrichthys, 391

    Erythrinus, 607

    Escholar, 437

    Esox, 624

    Etelis, 397

    Etheostomatidæ, 379

    Ethmoid, 57, 89

    Etroplus, 534

    Etrumeus, 662

    Euanemus, 572

    Euctenogobius, 487

    Euglyptosternum, 571

    Eugnathus, 368

    Eulachon, 647

    Eulepidotus, 368

    Euoxymetopon, 434

    Euprotomicrus, 334

    Europo-Asiatic region, 243

    Eurynotus, 370

    Eurypholis, 666

    Eurysomus, 370

    Eustira, 604

    Eutropiichthys, 566

    Eutropius, 566

    Evorthodus, 487

    Exoccipital, 56, 87

    Exocoetus, 621

    Exoglossum, 596

    Exostoma, 580

    Eye, 36, 111


    Fabricius, 13

    Fall-fish, 600

    Fierasfer, 549

    Fighting-fish, 519

    File-fishes, 684

    Fins, 40

    Fishing-Frog, 470

    Fistularia, 507, 508

    Fitzroyia, 615

    Flat-fishes, 553

    Flounder, 557

    Flute-mouth, 507

    Flying-fish, 621

    Flying Gurnard, 482

    Forskal, 13

    Forster, 13

    Freshwater-fishes, 208

    Freshwater-Herring, 645

    Fries and Ekström, 27

    Frog-fish, 470

    Frontal bone, 57, 89

    Frost-fish, 436

    Fuegian sub-region, 248

    Fundulus, 615


    Gadiculus, 541

    Gadidæ, 539

    Gadopsis, 537

    Gadus, 539

    Galapagoes district, 280

    Galaxias, 624

    Galeichthys, 569

    Galeocerdo, 317

    Galeoides, 425

    Galeus, 318

    Gallo, 451

    Gambusia, 616

    Ganodus, 349

    Ganoidei, 350

    Ganoid scales, 47

    Gar-pike, 367, 620

    Gaspereau, 659

    Gastrochisma, 455

    Gastrocnemus, 452

    Gastromyzon, 604

    Gastropelecus, 610

    Gastrosteus, 505

    Gastrotokeus, 682

    Gazza, 450

    Gegenbaur, 32

    Gempylus, 437

    Genidens, 569

    Genyoroge, 384

    Genypterus, 549

    Geoffroy, 33

    Geophagus, 537

    Geotria, 693

    Gerres, 388

    Gillaroo, 645

    Gill-cover, 38

    Gill-opening, 38

    Gill-rakers, 59, 139

    Gills, 136

    Gilthead, 409

    Ginglymostoma, 326

    Girardinus, 618

    Girella, 406

    Glanidium, 572

    Glanis, 566

    Glaucosoma, 384

    Globe-fish, 687

    Glossohyal, 58

    Glottis, 149

    Glut, 673

    Glutinous hag, 694

    Glyphidodon, 525

    Glyptauchen, 415

    Glyptolæmus, 365

    Glyptolepis, 365

    Glyptopomus, 365

    Glyptosternum, 572

    Gmelin, 13

    Gobiesocidæ, 510

    Gobiesox, 513

    Gobio, 595

    Gobiodon, 487

    Gobiosoma, 487

    Gobius, 486

    Goby, 486

    Gold-fish, 591

    Gold-Sinny, 527

    Gomphodus, 319

    Gomphosus, 530

    Gonatodus, 370

    Goniognathus, 452

    Gonorhynchus, 652

    Gonostoma, 629

    Gourami, 517

    Grammistes, 382

    Granular teeth, 126

    Graphiurus, 365

    Grayling, 649

    Greenland Shark, 333

    Grey Mullet, 501

    Grig, 673

    Gronow, 12

    Growler, 393

    Growth of Fishes, 170

    Grystes, 392

    Gudgeon, 596

    Gular plates, 80

    Güldenstedt, 13

    Gunellichthys, 498

    Gunnel-fish, 496

    Günther, 27, 30

    Gurnard, 479

    Gwyniad, 649

    Gymnachirus, 558

    Gymnarchus, 626

    Gymnelis, 538

    Gymnocrotaphus, 406

    Gymnocypris, 595

    Gymnomuræna, 677

    Gynmoscopelus, 585

    Gymnotus, 667

    Gyracanthus, 314

    Gyrodus, 367

    Gyropristis, 314

    Gyroptychius, 365


    Haddock, 540

    Hadot, 540

    Hæmal arches, 86

    Hæmal spine, 52

    Hæmapophyses, 51

    Hæmulon, 386

    Hag-fish, 694

    Hair-tail, 436

    Hake, 542

    Halargyreus, 541

    Halec, 656

    Halecidæ, 656

    Half-beak, 621

    Halidesmus, 549

    Halieutæa, 475

    Halieutichthys, 475

    Haliophis, 550

    Haller, 16

    Haloporphyrus, 543

    Halosauridæ, 665

    Hamilton, 17

    Hammerhead, 318

    Hapalogenys, 386

    Haplochilus, 615

    Haplochiton, 651

    Haplodactylina, 406

    Hapuku, 392

    Harpagifer, 467

    Harpodon, 583

    Harttia, 580

    Hasse, 32

    Hasselquist, 13

    Hausen, 361

    Head, 36

    Heart, 150

    Heckel, 28

    Hector, 32

    Heliastes, 525

    Helicophagus, 566

    Heliodus, 359

    Helmichthys, 180

    Helogenes, 567

    Helotes, 385

    Hemerocœtes, 491

    Hemichromis, 535

    Hemiculter, 604

    Hemigaleus, 319

    Hemigymnus, 530

    Hemilepidotus, 480

    Hemiodus, 607

    Hemipimelodus, 569

    Hemipristis, 317

    Hemirhamphus, 621

    Hemirhombus, 556

    Hemirhynchus, 437

    Hemisaurida, 582

    Hemisilurus, 566

    Hemisorubim, 568

    Hemithyrsites, 434

    Hemitrichas, 656

    Hemitripterus, 417

    Heniochus, 399

    Heptanchus, 325

    Heptapterus, 581

    Hermaphroditism, 157

    Heros, 536

    Herring, 658

    Heteracanth, 41

    Heterobranchus, 563

    Heterocercy, 80

    Heteroconger, 674

    Heterognathodon, 389

    Heterolepidotidæ, 491

    Heteropygii, 618

    Heterostichus, 498

    Heterotis, 655

    Hexanchus, 325

    Hexapsephus, 588

    Himantolophus, 472

    Hippocampus, 683

    Hippoglossoides, 555

    Hippoglossus, 555

    Histiophorus, 431

    Histiopterus, 387

    Holacanthus, 400

    Holibut, 555

    Hollardia, 684

    Holocentrum, 423

    Holocephala, 348

    Holophagus, 365

    Holoptychidæ, 365

    Holosteus, 619

    Homacanth, 41

    Homaloptera, 604

    Hombron et Jacquinot, 27

    Homelyn Ray, 341

    Homocanthus, 314

    Homocercy, 83

    Homoeolepis, 366

    Homonotus, 421

    Hopladelus, 568

    Hoplichthys, 478

    Hoplognathus, 410

    Hoplopleuridæ, 665

    Hoplopteryx, 421

    Hoplopygus, 365

    Hoplostethus, 421

    Hoplunnis, 674

    Horse-mackerel, 442

    Hounds, 319

    Huchen, 645

    Humeral arch, 59

    Hunds-fish, 619

    Hunter, 16

    Huro, 393

    Hutton, 32

    Huxley, 33

    Hybernation, 188

    Hybodontidæ, 328

    Hybognathus, 596

    Hyborhynchus, 596

    Hybridism, 178

    Hydrocyon, 611

    Hygrogonus, 536

    Hyodon, 653

    Hyoid arch, 58

    Hyomandibular, 55, 89

    Hyoprorus, 674

    Hyoptopoma, 578

    Hyostylic skull, 74

    Hypamia, 372

    Hyperoglyphe, 387

    Hyperopisus, 625

    Hypnos, 340

    Hypobranchial, 58

    Hypomessus, 647

    Hypophthalmichthys, 602

    Hypophthalmus, 566

    Hypophysis, 98

    Hypotympanic, 55

    Hypsinotus, 402

    Hypsodon, 500

    Hypural, 53, 84

    Hyrtl, 32

    Hysterocarpus, 534

    Hystricodon, 611


    Icelus, 477

    Ichthyborus, 612

    Ichthyocampus, 681

    Ichthyodorulites, 194

    Ichthyomyzon, 693

    Id, 599

    Ikan sumpit, 403

    Impregnation, artificial, 186

    Indian region, 220

    Indo-Pacific ocean, 278

    Infraorbital, 54

    Infundibulum, 98

    Interhæmals, 53

    Intermaxillary, 53

    Interneurals, 53

    Interoperculum, 38, 55, 91

    Intestine, 127

    Ipnops, 585

    Ischyodus, 349

    Ischyrocephalus, 666

    Isistius, 334

    Isthmus, 39, 58

    Isurus, 457


    Japanese District, 270

    Jenyns, 27

    Jenynsia, 616

    John Dory, 451

    Jugular fins, 42

    Julis, 529


    Kabeljau, 540

    Kalm, 13

    Kamtschatkan district, 269

    Karausche, 591

    Karpfen, 589

    Kathetostoma, 463

    Kaup, 33

    Kelb el bahr, 611

    Kelb el moyeh, 611

    Kelp-fish, 533

    Keris, 440

    Ketengus, 569

    Kidney, 155

    King of the herrings, 522

    Klein, 12

    Klipvisch, 549

    Klunzinger, 30

    Kner, 27, 28

    Kneria, 606

    Kokopu, 625

    Kölliker, 32

    Kovalevsky, 33

    Kröyer, 27

    Kurtus, 425


    Labberdan, 540

    Labeo, 593

    Labials, 64, 69

    Labrax, 376

    Labrichthys, 530

    Labridæ, 525

    Labroides, 530

    Labrus, 526

    Labyrinthici, 514

    Lachnolæmus, 528

    Lachs, 644

    Lacépède, 15

    Lactarius, 450

    Ladislavia, 596

    Læmargus, 333

    Læmonema, 543

    Læops, 557

    Lais, 566

    Laminæ branchiales, 136

    Lamna, 320

    Lamnidæ, 319

    Lampern, 692

    Lampris, 454

    Lamprey, 692

    Lancelet, 696

    Lanioperca, 397

    Larimus, 431

    Lateral line, 48

    Lates, 377

    Latilus, 466

    Latris, 412

    Latrunculus, 486

    Launce, 550

    Leather-carp, 591

    Lebiasina, 607

    Lemon-sole, 558

    Lentipes, 487

    Lepadogaster, 513

    Lepidoblennius, 498

    Lepidocephalichthys, 606

    Lepidocephalus, 606

    Lepidocottus, 476

    Lepidopsetta, 556

    Lepidopus, 435

    Lepidosiren, 355

    Lepidosteidæ, 367

    Lepidotrigla, 479

    Lepidotus, 368

    Lepidozygus, 525

    Leporinus, 608

    Lepracanthus, 314

    Leptacanthus, 314

    Leptobarbus, 597

    Leptocarcharias, 319

    Leptocardii, 696

    Leptocephali, 179

    Leptoichthys, 681

    Leptojulis, 529

    Leptolepidæ, 371

    Leptopterygius, 513

    Leptoscopus, 463

    Leptosomus, 656

    Leptotrachelus, 666

    Lesson, 26

    Lethrinus, 407

    Leucaspius, 604

    Leuciscus, 598

    Leucosomus, 600

    Liacanthus, 314

    Liachirus, 558

    Liassic fishes, 198

    Lichia, 446

    Ligamentum longitudinale, 72

    Limnurgus, 615

    Ling, 544, 549

    Linnæus, 10

    Liocassis, 567

    Liopsetta, 556

    Lioscorpius, 415

    Liparis, 485

    Liposarcus, 576

    Liver, 132

    Loach, 604

    Lobotes, 387

    Lonchurus, 431

    Lophiogobius, 487

    Lophiosilurus, 569

    Lophiostomus, 368

    Lophius, 470

    Lophobranchii, 678

    Lophonectes, 556

    Loricaria, 578

    Lota, 544

    Lotella, 543

    Loxodon, 319

    Lucania, 615

    Lucifuga, 547

    Luciocephalidæ, 519

    Luciogobius, 489

    Lucioperca, 378

    Luciosoma, 598

    Luciotrutta, 646

    Lump-sucker, 484

    Lütken, 32

    Lycodes, 537


    Mackerel, 456, 457

    Mackerel Midge, 544

    Macrodon, 607

    Macrolepis, 421

    Macrones, 567

    Macropoma, 365

    Macropus, 517

    Macrosemius, 368

    Macruridæ, 557

    Macruronus, 552

    Macrurus, 552

    Mæna, 390

    Mahaseer, 594

    Malacanthus, 467

    Malacocephalus, 552

    Malacopterus, 528

    Malacopterygian, 41

    Malacosteus, 629

    Malapterurus, 574

    Mallotus, 647

    Malpighi, 7

    Malpighian corpuscle, 155

    Malthe, 475

    Mandible, 54

    Margrav, 7

    Marine fishes, 254

    Mary sole, 555

    Maskinonge, 624

    Mastacembelus, 498

    Mastoid, 57, 88

    Maurolicus, 628

    Maynea, 538

    Maxillary, 53, 90

    Meagre, 427

    Meckel’s cartilage, 54

    Meda, 601

    Mediterranean  district, 264

    Medulla oblongata, 98

    Megalichthys, 365

    Megalobrycon, 610

    Megalops, 661

    Meidinger, 13

    Melamphaes, 423

    Melanocetus, 473

    Melanonus, 541

    Membrane-bones, 75, 84

    Mendosoma, 412

    Mene, 455

    Menhaden, 659

    Merluccius, 542

    Mesencephalon, 97

    Mesoarium, 158

    Mesodon, 367

    Mesogaster, 500

    Mesolepis, 370

    Mesonauta, 536

    Mesoprion, 384

    Mesops, 537

    Mesopterygium, 70

    Mesotympanic, 55

    Mesturus, 367

    Metacarpals, 59

    Metamorphosis, 170

    Metapterygium, 70

    Metapterygoid, 55, 90

    Metencephalon, 97

    Micracanthus, 519

    Microconodus, 370

    Microdesmus, 538

    Microdon, 367

    Micropogon, 428

    Micropteryx, 443

    Micropus, 416

    Microstoma, 650

    Miller’s-thumb, 476

    Minnow, 596, 599

    Minous, 417

    Misgurnus, 604

    Mishcup, 408

    Mitchell, 17

    Mixogamous, 177

    Mollienesia, 617

    Molva, 544

    Monacanthus, 684

    Monk-fish, 334

    Monocentris, 421

    Monocirrhus, 418

    Monopterus, 669

    Moon-eye, 653

    Mora, 541

    Mordacia, 693

    Moringua, 675

    Mormyrops, 626

    Mormyrus, 625

    Mossbanker, 659

    Motella, 544

    Mouth, 37, 123

    Moxostoma, 589

    Mud-fish, 372, 619

    Mugil, 501

    Müller, H., 33

    Müller, J., 22, 32, 33

    Müller, O. F., 13

    Müller, W., 33

    Mullidæ, 403

    Mulloides, 404

    Mullus, 404

    Munro, 16

    Muræna, 675

    Murænesox, 674

    Murænichthys, 674

    Murænolepis, 545

    Murray-Cod, 392

    Muscles, 93

    Muskellunge, 624

    Mustelus, 318

    Mylesinus, 613

    Myletes, 613

    Myliobatis, 344

    Mylocyprinus, 588

    Myloleucus, 601

    Mylopharodon, 601

    Myology, 93

    Myriacanthus, 314

    Myriodon, 383

    Myriolepis, 370

    Myripristis, 423

    Myroconger, 677

    Myrophis, 674

    Myrus, 674

    Mystacoleucus, 598

    Myxine, 695

    Myxodes, 498

    Myxus, 504


    Nandus, 418

    Nannœthiops, 610

    Nannobrachium, 587

    Nannocampus, 681

    Nannocharax, 608

    Nannostomus, 607

    Narcine, 340

    Naseus, 438, 440

    Nauclerus, 446

    Naucrates, 444

    Nautichthys, 480

    Nealotus, 434

    Nearctic region, 246

    Nebris, 431

    Nebrius, 326

    Neetroplus, 536

    Nefasch, 612

    Nemacanthus, 314

    Nemachilus, 605

    Nemadactylus, 412

    Nematogenys, 581

    Nematops, 557

    Nematoptychius, 370

    Nemichthys, 670

    Nemophis, 498

    Nemopteryx, 434, 539

    Neochanna, 624

    Neoclinus, 498

    Neoconger, 674

    Neophrynichthys, 469

    Neotropical region, 233

    Nerfling, 599

    Nerophis, 681

    Nerves, 103

    Nesiarchus, 434

    Nettastoma, 674

    Neural arches, 85

    Neural spine, 52

    Neurapophyses, 51

    Neurology, 96

    Neuroskeleton, 85

    New Zealand sub-region, 248

    Nictitating  membrane, 113

    Nilsson, 27

    Niphon, 397

    Nomeidæ, 455

    Nomeus, 456

    Nonnat, 501

    Nordmann, 28

    North American district, 266

    North American region, 246

    North Atlantic, 262

    Northern temperate zone, 262

    Northern zone, 240

    North Pacific, 268

    Nostrils, 37, 109

    Notacanthus, 523

    Notidanus, 325

    Notochord, 63

    Notoglanis, 569

    Notograptus, 498

    Notopterus, 665

    Notothenia, 466

    Noturus, 568

    Novacula, 529

    Nummopalatus, 526

    Nuria, 598

    Nutrition, organs of, 121


    Oar-Fish, 522

    Oblata, 406

    Occipital, 56

    Ochetobius, 602

    Odax, 532

    Odontaspis, 321

    Odonteus, 525

    Odontostomus, 587

    Oil-sardine, 660

    Old Red Sandstone, 194

    Old wife, 406

    Olfactory lobes, 97

    Olfactory organ, 109

    Oligorus, 392

    Oligosarcus, 611

    Olistherops, 533

    Ombre, 429

    Ombre chevalier, 645

    Omentum, 132

    Onchus, 314

    Oncorhynchus, 646

    Oneirodes, 473

    Oolithic fishes, 199

    Opercular gill, 138

    Operculum, 38, 54, 91

    Ophichthys, 674

    Ophidiidæ, 546

    Ophidium, 549

    Ophiocephalidæ, 513

    Ophiodon, 491

    Ophiopsis, 368

    Opisthognathus, 466

    Opisthopteryx, 656

    Opisthoticum, 88

    Opsariichthys, 602

    Optic lobes, 97

    Oracanthus, 314

    Orbitosphenoid, 57, 88

    Oreinus, 595

    Oreonectes, 606

    Orestias, 615

    Orfe, 599

    Orthacanthus, 334

    Orthagoriscus, 690

    Orthodon, 601

    Orthostomus, 489

    Osbeck, 13

    Osmeroides, 582, 631

    Osmerus, 646

    Os operculare, 91

    Osphromenus, 517

    Osteobrama, 604

    Osteochilus, 596

    Osteogeniosus, 569

    Osteoglossum, 654

    Osteolepis, 365

    Ostracion, 686

    Os transversum, 56

    Otolith, 116

    Otolithus, 430

    Oulachon, 647

    Ovaries, 158, 166

    Ovum, 158, 159, 167

    Owen, 33

    Oxuderces, 489

    Oxyconger, 674

    Oxydoras, 572

    Oxygnathus, 370

    Oxymetopon, 489

    Oxyrhina, 320

    Oxytes, 319


    Pachycormus, 368

    Pachymetopon, 406

    Pachyurus, 430

    Pagellus, 408

    Pagrus, 408

    Paired fins, 42

    Palæarctic region, 243

    Palæichthyes, 312

    Palæogadus, 539

    Palæoniscidæ, 369

    Palæorhynchus, 437

    Palæeoscyllium, 326

    Palæospinax, 330

    Palatine, 56, 90

    Palatine arch, 55

    Palimphyes, 457

    Pallas, 13

    Pammelas, 447

    Pancreas, 133

    Pangasius, 566

    Pantodon, 653

    Papilla urogenitalis, 156

    Paracanthobrama, 598

    Paradiplomystax, 569

    Paradise-fish, 517

    Paragoniates, 610

    Paralepis, 585

    Paralichthys, 556

    Paramisgurnus, 606

    Paramyrus, 674

    Paraperca, 375

    Paraphoxinus, 601

    Parapophyses, 51

    Parascopelus, 582

    Parascyllium, 326

    Parasphenoid, 56, 89

    Pardachirus, 558

    Paretroplus, 535

    Parietals, 57, 89

    Pariodon, 581

    Parker, 32

    Parma, 525

    Parnell, 27

    Paroccipital, 56, 88

    Parodon, 607

    Parophrys, 557

    Paropsis, 450

    Parra, 13

    Parr-marks, 631

    Parrot-wrasses, 530

    Patæcus, 497

    Patagonian district, 289

    Peal, 644

    Pectoral arch, 92

    Pectoral fins, 42

    Pediculati, 469

    Pegasus, 482

    Pelagic fishes, 292

    Pelamys, 459

    Pelargorhynchus, 666

    Pelecus, 604

    Pelerin, 322

    Pellona, 660

    Pellonula, 660

    Pelor, 417

    Pelotrophus, 604

    Peltorhamphus, 557

    Pempheris, 425

    Pennant, 13

    Pentaceros, 397

    Pentanemus, 425

    Pentapus, 390

    Pentaroge, 417

    Perca, 375

    Percalabrax, 378

    Perch, 375

    Percichthys, 376

    Percidæ, 375

    Percilia, 397

    Percis, 464

    Percophis, 466

    Percopsis, 651

    Periophthalmus, 487

    Peristethus, 481

    Permian fishes, 197

    Peruvian district, 280

    Pesce Rey, 501

    Petalopteryx, 480

    Petenia, 536

    Peters, 31

    Petrodus, 329

    Petromyzon, 692

    Petrosal, 56

    Petroscirtes, 494

    Phaneropleuridæ, 360

    Pharyngeal bones, 58

    Pharyngognathi, 523

    Pholidichthys, 498

    Pholidophorus, 368

    Photichthys, 629

    Phractocephalus, 568

    Phrynorhombus, 555

    Phycis, 543

    Phyllodus, 526

    Phyllopteryx, 682

    Physiculus, 543

    Physostomi, 559

    Piabuca, 610

    Piabucina, 610

    Pickerell, 624

    Pike, 624

    Pike-perch, 378

    Pilchard, 660

    Pileoma, 379

    Pilot-fish, 444

    Pimelepterus, 410

    Pimelodus, 568

    Pimephales, 596

    Pinguipes, 466

    Pipe-fishes, 680

    Piramutana, 568

    Piratinga, 568

    Pirinampus, 569

    Piso, 7

    Pituitary gland, 98

    Placodermi, 351

    Placoid scales, 48

    Plagiostomata, 313

    Plagiotremus, 498

    Plagusia, 559

    Plagyodus, 586

    Plaice, 557

    Pla-kat, 519

    Platax, 448

    Platinx, 656

    Platycephalus, 477

    Platycornus, 421

    Platyglossus, 529

    Platynematichthys, 566

    Platypoecilus, 618

    Platyptera, 489

    Platyrhina, 342

    Platysomidæ, 370

    Platystethus, 450

    Platystoma, 568

    Platystomatichthys, 568

    Platytroctes, 664

    Playfair, 29

    Plecoglossus, 646

    Plecostomus, 576

    Plectropoma, 382

    Plesiops, 418

    Pleurapophyses, 52

    Pleurolepidæ, 366

    Pleuronectes, 557

    Pleuronectidæ, 553

    Pleuropholis, 368

    Plinthophorus, 666

    Plionemus, 442

    Plotosus, 563

    Podabrus, 480

    Podocys, 421

    Poecilia, 617

    Poeciloconger, 674

    Poecilopsetta, 557

    Poey, F., 31

    Pogonias, 427

    Poisonous fishes, 189

    Poisson bleu, 650

    Pollack, 541

    Pollan, 649

    Polyacanthus, 516

    Polycaulus, 480

    Polycentrus, 418

    Polyipnus, 628

    Polymixia, 423

    Polynemus, 425

    Polyodontidæ, 362

    Polyprion, 382

    Polypteroidei, 363

    Polypterus, 364

    Polyrhizodus, 330

    Pomacanthus, 401

    Pomacentrus, 525

    Pomatomus, 395

    Pomotis, 396

    Pompilus, 444

    Pope, 378

    Porbeagle, 320

    Porgy, 408

    Porichthys, 468

    Portheus, 500

    Porthmeus, 446

    Port Jackson Shark, 330

    Porus abdominalis, 123

    Porus genitalis, 123, 158

    Postclavicula, 59, 92

    Postfrontal bone, 57, 89

    Post-pliocene fishes, 201

    Post-temporal, 59, 92

    Pout, 541

    Powen, 649

    Præoperculum, 38, 54, 90

    Præorbital, 54

    Prefrontal, 57, 89

    Premaxillary, 53, 90

    Premnas, 525

    Preñadillas, 575

    Pretympanic, 55

    Priacanthus, 395

    Pride, 693

    Prionotus, 479

    Prionurus, 440

    Pristacanthus, 314

    Pristidæ, 336

    Pristigaster, 660

    Pristiophorus, 335

    Pristipoma, 385

    Pristis, 337

    Pristiurus, 326

    Prochilodus, 607

    Prooticum, 88

    Propterus, 368

    Propterygium, 70

    Prosencephalon, 97

    Prosopodasys, 417

    Protamia, 372

    Protocampus, 681

    Protopterus, 356

    Protosphyræna, 500

    Prototroctes, 652

    Prussian carp, 591

    Psaliodus, 349

    Psammobatis, 342

    Psammodiscus, 557

    Psammodus, 329

    Psammoperca, 378

    Psenes, 456

    Psephurus, 363

    Psettichthys, 556

    Psettodes, 554

    Psettus, 447

    Pseudecheneis, 580

    Pseudeutropius, 566

    Pseudobagrus, 567

    Pseudoberyx, 421

    Pseudoblennius, 498

    Pseudobranchiæ, 140

    Pseudochalceus, 610

    Pseudochilinus, 530

    Pseudochromis, 466

    Pseudodax, 530

    Pseudoeleginus, 462

    Pseudogobio, 596

    Pseudojulis, 529

    Pseudolabuca, 604

    Pseudoperilampus, 601

    Pseudophycis, 542

    Pseudoplesiops, 466

    Pseudorasbora, 596

    Pseudorhombus, 556

    Pseudoscarus, 532

    Pseudosyngnathus, 680

    Pseudovomer, 442

    Pseudoxiphophorus, 617

    Psilorhynchus, 604

    Psychrolutes, 469

    Pteraclis, 455

    Pteragogus, 530

    Pteraspis, 354

    Pterichthys, 351

    Pteroplatea, 344

    Pteridium, 549

    Pterois, 415

    Pterophyllum, 537

    Pteropsarion, 602

    Pterygocephalus, 492

    Pterygoid, 56

    Pterygoplichthys, 576

    Ptychacanthus, 314

    Ptychobarbus, 595

    Ptychodus, 330

    Ptycholepis, 368

    Ptyonotus, 480

    Pycnodontidæ, 366

    Pygopterus, 370

    Pyloric appendages, 131

    Pyrrhulina, 607


    Quadrate Bone, 55, 89

    Quoy et Gaimard, 26


    Radius, 59

    Raja, 340

    Raniceps, 544

    Rasbora, 597

    Rasborichthys, 604

    Rathke, 32

    Ray, 8

    Rays of fins, 40

    Rays, 335, 341

    Red bodies, 147

    Red-dace, 599

    Red-eye, 599

    Red-fin, 599

    Red-horse, 589

    Red mullet, 404

    Regalecus, 522

    Reproduction of lost parts, 188

    Reproduction, organs of, 157

    Respiration, organs of, 135

    Rete mirabile, 147

    Retropinna, 647

    Retzius, 32

    Rhabdolepis, 370

    Rhacolepis, 421

    Rhadinichthys, 370

    Rhamphichthys, 666

    Rhamphocottus, 480

    Rhamphosus, 507

    Rhina, 334

    Rhinelepis, 576

    Rhinellus, 656

    Rhinichthys, 596

    Rhinobatus, 338

    Rhinodon, 323

    Rhinodoras, 572

    Rhinoglanis, 573

    Rhinonus, 549

    Rhinoptera, 346

    Rhizodus, 365

    Rhodeus, 601

    Rhomboidichthys, 556

    Rhombosolea, 557

    Rhombus, 555

    Rhynchichthys, 424

    Rhynchobatus, 337

    Rhynchobdella, 498

    Rhynchodus, 349

    Rhypticus, 383

    Rhytiodus, 608

    Rib, 52

    Ribbon-fishes, 520

    Richardson, 27, 28

    Risso, 17

    Rita, 567

    Rivulus, 615

    Roach, 599, 600

    Rock-cook, 528

    Rockling, 544

    Rohteichthys, 597

    Rondelet, 5

    Rosenthal, 32

    Rough Dab, 555

    Rudd, 599

    Rüppell, 29

    Russel, 16


    Saccarius, 474

    Saccobranchus, 565

    Saccodon, 607

    Saccopharynx, 670

    Sælbling, 645

    Sail-fish, 589

    Sail-fluke, 555

    Salanx, 650

    Salarias, 494

    Salivary glands, 124

    Salminus, 611

    Salmo, 631

    Salmon, 644

    Salmon-trout, 644

    Salvelini, 645

    Salviani, 5

    Samaris, 556

    Sand-eel, 550

    Sand-piper, 693

    Sandy Ray, 341

    Sar, 406

    Saragu, 406

    Sarcodaces, 611

    Sardine, 660

    Sargina, 406

    Sargo, 406

    Sargodon, 405

    Sargus, 406

    Satanoperca, 537

    Saurenchelys, 674

    Saurichthys, 365

    Saurida, 582

    Sauridæ, 368

    Saurocephalus, 500

    Saurodipteridæ, 355

    Saurodontidæ, 500

    Saurorhamphus, 666

    Saurus, 582

    Saury, 620

    Saw-fishes, 337

    Scabbard-fish, 435

    Scald-fish, 556

    Scales, 45

    Scaphaspis, 354

    Scaphirhynchus, 362

    Scapula, 59, 92

    Scapular arch, 59

    Scarichthys, 531

    Scarus, 526, 530

    Scatharus, 406

    Scatophagus, 401

    Schacra, 602

    Schal, 573

    Schedophilus, 455

    Schell-fisch, 540

    Schelly, 649

    Schilbe, 566

    Schilbichthys, 566

    Schizopygopsis, 595

    Schizothorax, 595

    Schlegel, 29

    Schneider, 15

    Schultze, 33

    Sciades, 568

    Sciæna, 429

    Sciænidæ, 426

    Scissor, 610

    Sclerodermi, 684

    Sclerognathus, 589

    Scolopsis, 389

    Scomber, 457

    Scombresox, 620

    Scombridæ, 456

    Scombroclupea, 656

    Scombrops, 395

    Scopelidæ, 582

    Scopelosaurus, 587

    Scopelus, 584

    Scorpæna, 444

    Scorpænichthys, 480

    Scorpænidæ, 412

    Scorpis, 402

    Scup, 408

    Scylliodus, 326

    Scyllium, 325

    Scymnus, 332

    Sea-bat, 448

    Sea-bream, 405, 408

    Sea-cat, 493

    Sea-devil, 344, 470

    Sea-hedgehog, 687

    Sea-horses, 682

    Sea-perch, 381

    Sea-serpents, 521

    Sea-trout, 644

    Sea-wolf, 493

    Seba, 9

    Sebastes, 413

    Secondary sexual characters, 176

    Seingo, 378

    Selache, 322

    Selachoidei, 314

    Semicossyphus, 530

    Semionotus, 368

    Semiophorus, 441, 442

    Semiplotus, 598

    Seriola, 444

    Seriolella, 444, 450

    Seriolichthys, 444

    Serranus, 381

    Serrasalmo, 613

    Setiform teeth, 126

    Sewin, 644

    Sexual characters, 176

    Shad, 659

    Shagreen, 315

    Shagreen Skate, 341

    Sharks, 314

    Shark’s fins, 315

    Sheep’s head, 406

    Shiner, 599, 603

    Shore-fishes, 257

    Sicyases, 513

    Sicydium, 487

    Siebold, 28

    Sillago, 464

    Silondia, 566

    Siluranodon, 566

    Silurian fishes, 193

    Silurichthys, 566

    Siluridæ, 559

    Siluris, 565

    Siniperca, 376

    Sinus rhomboidalis, 99

    Siphagonus, 481

    Siphonal stomach, 130

    Siphonognathus, 533

    Siphonostoma, 680

    Sirembo, 549

    Sirenidæ, 355

    Sisor, 580

    Skate, 341

    Skeleton of--
      Amia, 82
      Amphioxus, 63
      Chondropterygians, 66
      Chondrostei, 74
      Cyclostomes, 64
      Dipnoi, 71
      Ganoids, 71
      Lepidosteus, 80
      Polypterus, 77
      Teleostei, 83

    Skin, 45

    Skip-jack, 447

    Skipper, 620

    Skull, 51, 85

    Skulpin, 489

    Smaris, 390

    Smear-dab, 557

    Smelt, 647

    Smerdis, 375

    Smiliogaster, 604

    Snapper, 408

    Snock, 437

    Snout, 37

    Solander, 13

    Sole, 557

    Solea, 557

    Solenognathus, 682

    Solenorhynchus, 678

    Solenostoma, 678

    Soleotalpa, 559

    Sonnerat, 13

    Soricidens, 405

    Sorubim, 568

    South Australian district, 283

    Southern temperate zone, 281

    Southern zone, 248

    Spaniodon, 656

    Sparidæ, 405

    Sparnodus, 405

    Sparoid scales, 46

    Spathobatis, 338

    Spathodactylus, 656

    Spatularia, 362

    Spawn-eater, 599

    Spear-fish, 589

    Sphærodon, 408

    Sphærodontidæ, 368

    Sphenacanthus, 314

    Sphenocephalus, 421

    Sphenodus, 319

    Sphenoid, 57

    Sphenoideum anterius, 89

    Sphyræna, 499

    Sphyrænodus, 500

    Spiegel-Karpfen, 591

    Spinacidæ, 330

    Spinal chord, 96

    Spinal column, 51

    Spinax, 332

    Spines of fins, 40

    Spiracles, 138

    Spiral valve, 128

    Spirobranchus, 516

    Splanchnoskeleton, 85

    Spleen, 133

    Splenial, 54, 91

    Sprat, 659

    Spratelloides, 662

    Squaliobarbus, 602

    Squaloraja, 335

    Squamipinnes, 397

    Squamosal, 88, 89

    Stannius, 32, 33

    Stare-gazer, 462

    Starry Ray, 341

    Stegophilus, 581

    Stegostoma, 326

    Steindachner, 28

    Steller, 13

    Stenostoma, 421

    Sterlet, 361

    Sternarchus, 666

    Sternoptyx, 627

    Sternopygus, 667

    Stethojulis, 529

    Stichæopsis, 498

    Stichæus, 495

    Sticharium, 498

    Stickleback, 505

    Stigmatophora, 681

    Sting Rays, 342

    Stock-fish, 540, 542

    Stomach, 127

    Stomias, 629

    Stone-bass, 382

    Stone-lugger, 596

    Stone-roller, 589

    Stone Toter, 596

    Storer, 29

    Strepsodus, 365

    Strinsia, 541

    Stromateus, 452

    Strophodus, 330

    Sturgeons, 361

    Stygogenes, 575

    Stylodontidæ, 368

    Stylohyal, 58

    Stylophorus, 522

    Suboperculum, 38, 55, 91

    Suborbital, 91

    Sucker, 588

    Sucking-fish, 460

    Sudis, 586

    Sun-fishes, 396, 454, 690

    Supraclavicula, 59, 92

    Supraoccipital, 56, 87

    Supraorbital, 89

    Suprascapula, 59

    Supratemporal, 91

    Surgeon, 439

    Suspensorium of mandible, 55

    Swammerdam, 7

    Sword-fish, 431

    Symbranchus, 669

    Sympathic nerves, 108

    Symphorus, 390

    Symphysis, 54

    Symphysodon, 537

    Symplectic, 55, 89

    Sympterygia, 342

    Synagris, 390

    Synanceia, 416

    Synaphobranchus, 671

    Synaptura, 558

    Syngnathus, 680

    Synodontis, 573


    Taenianotus, 417

    Taeniura, 343

    Taractes, 454

    Tasmanian sub-region, 248

    Taste, organ of, 119

    Taurinichthys, 526

    Tautoga, 527

    Teeth, 121, 124

    Teleostei, 373

    Telescope-fish, 592

    Tellia, 615

    Temera, 340

    Temnodon, 446

    Tenacity of life, 186

    Tench, 600

    Tephraeops, 406

    Tephritis, 555

    Tertiary fishes, 200

    Testicles, 162, 167

    Tetragonolepis, 368

    Tetragonopterus, 609

    Tetragonurus, 501

    Tetranematichthys, 572

    Tetraroge, 417

    Tetrodon, 688

    Teuthididæ, 418

    Teuthis, 419

    Thalassophryne, 468

    Thalassorhinus, 319

    Thaleichthys, 647

    Thaumas, 334

    Thectodus, 330

    Therapon, 385

    Tholichthys, 172

    Thoracic fins, 42

    Thornback, 341

    Thrissonotus, 370

    Thrissopater, 656

    Thrissops, 371

    Thunberg, 13

    Thymallus, 649

    Thynnichthys, 595

    Thynnus, 457

    Thyrsites, 436

    Thysanopsetta, 556

    Tiger-shark, 327

    Tilurus, 180

    Tinca, 599

    Tongue, 124

    Tope, 318

    Top-knot, 555

    Torgoch, 645

    Torpedinidæ, 338

    Torpedo, 339

    Torsk, 546

    Touch, organ of, 120

    Toxabramis, 604

    Toxotes, 403

    Trachelochismus, 513

    Trachelyopterus, 572

    Trachichthys, 422

    Trachinidæ, 462

    Trachinops, 418

    Trachinopsis, 462

    Trachinus, 463

    Trachurus, 442

    Trachynotus, 447

    Trachypterus, 522

    Transverse line, 50

    Triacanthodes, 684

    Triacanthus, 684

    Triacis, 319

    Triænodon, 319

    Triænophorichthys, 487

    Triassic fishes, 197

    Trichiurichthys, 434

    Trichiuridæ, 433

    Trichiurus, 436

    Trichocyclus, 689

    Trichodiodon, 689

    Trichodon, 466

    Trichogaster, 518

    Trichomycterus, 581

    Trichonotus, 490

    Trichopleura, 417

    Trifurcated Hake, 545

    Trigla, 478

    Triglops, 480

    Trigorhina, 338

    Triodon, 687

    Tripterodon, 406

    Tripterygium, 495

    Tristichopterus, 365

    Tristychius, 314

    Trochocopus, 530

    Tropical American region, 233

    Trout, 644

    Trubu, 660

    Trumpeter, 412

    Trumpet-fish, 509

    Trunk, 39

    Trygon, 343

    Trygonidæ, 342

    Trygonorhina, 338

    Trypauchen, 489

    Tunny, 458

    Turbinal, 57, 91

    Turbot, 555

    Twaite Shad, 659

    Tyellina, 326

    Tylognathus, 596

    Typhlichthys, 618

    Typhlonus, 548


    Uaru, 536

    Ulna, 59

    Umbra, 429, 619

    Umbrina, 428

    Umbrine, 429

    Undina, 365

    Upeneichthys, 404

    Upeneoides, 404

    Upeneus, 404

    Upokororo, 652

    Uraleptus, 543

    Uranoscopus, 462

    Urinary organs, 155

    Urocampus, 681

    Urocentrus, 498

    Uroconger, 674

    Urogymnus, 343

    Urohyal, 58, 91

    Urolophus, 343

    Uronectes, 538

    Uronemus, 360

    Urosphen, 507

    Urosthenes, 370

    Useful fishes, 189


    Vaillant, 31

    Valenciennes, 18

    Vandellia, 581

    Velifer, 397

    Vendace, 649

    Ventral fins, 42

    Vertebral column, 51

    Vertical fins, 40

    Villiform teeth, 126

    Viviparous Blenny, 497

    Vogt, 32

    Vomer (bone), 56, 89

    Vomer (gen.), 441

    Vulsus, 489


    Wallago, 566

    Wardichthys, 370

    Weever, 464

    Wels, 565

    Whiff, 555

    White-bait, 658

    White-fish, 599, 648

    Whiting, 541

    Whiting-pout, 541

    Willughby, 8

    Wrasses, 525


    Xenocephalus, 553

    Xenocharax, 612

    Xenocypris, 598

    Xenodermichthys, 664

    Xenomystus, 576

    Xenopterus, 688

    Xiphias, 431

    Xiphidion, 496

    Xiphiidæ, 431

    Xiphochilus, 530

    Xiphopterus, 434

    Xiphorhampus, 611

    Xiphostoma, 611


    Yarrell, 27

    Yellow-tail, 444


    Zanchus, 449

    Zaniolepis, 491

    Zärthe, 603

    Zebra-Shark, 327

    Zeus, 451

    Zoarces, 497

    Zope, 603

    Zuzuki, 378

    Zygaena, 318

    Zygapophyses, 52

    Zygobatis, 346


                               THE END.


               _Printed by_ R. & R. CLARK, _Edinburgh_.


FOOTNOTES:

[1] From ιχθυς, fish, and λογος, doctrine or treatise.

[2] Down to this period the history of Ichthyology is fully treated in
the first volume of Cuvier and Valenciennes “Hist. nat. d. Poiss.”

[3] Description of Ceratodus. “Phil. Trans.,” 1871, ii.

[4] In the formula generally preceding the description of a fish, “L.
lat. 40,” would express that the scales between the head and caudal fin
are arranged in 40 transverse series; and probably, that the lateral
line is composed of the same number of scales. “L. transv. 8/5” would
express that there are eight longitudinal series of scales between the
median line of the back and the lateral line, and five between the
lateral line and the middle of the abdomen.

[5] Pterotic of Parker.

[6] _C. Hasse_ has studied the modifications of the texture of the
vertebræ and the structure of the Chondropterygian skeleton generally,
and shown that they correspond in the main to the natural groups of
the system, and, consequently, that they offer a valuable guide in the
determination of fossil remains.

[7] The Ganoids formed at former epochs the largest and most important
order of fishes, many of the fossil forms being known from very
imperfect remains only. It is quite possible that not a few of
the latter, in which nothing whatever of the (probably very soft)
endoskeleton has been preserved, should have to be assigned to some
other order lower in the scale of organisation than the Ganoids (for
instance, the _Cephalaspidæ_).

[8] As first proposed by Huxley.

[9] Stannius (pp. 60, 65) doubts the pure origin of these two bones
from membranous tissue, and is inclined to consider them as “the
extreme end of the abortive axial system.”

[10] Parker’s nomenclature is adopted here.

[11] According to _Langerhans_ “Untersuchungen über Petromyzon
planeri” (Freiburg, 1873) an optic chiasma exists in that species.

[12] This nerve is not shown in the figure of the brain of the Perch
(Fig. 41), as reproduced above from Cuvier.

[13] Müller considers a nerve rising jointly with the Vagus in
Petromyzon to be this nerve (Fig. 45, _hy_).

[14] On the development and structure of the dentition of _Scarina_,
see _Boas_, “Die Zähne der Scaroiden,” in Zeitschr. f. Wiss. Zoolog.
xxxii. (1878).

[15] This applies to individuals only growing up under normal
conditions. Dr. H. A. Meyer has made observations on young Herrings.
Individuals living in the sea had attained at the end of the third
month a length of 45 to 50 millimetres, whilst those reared from
artificially-impregnated ova were only from 30 to 35 millimetres long.
When the latter had been supplied with more abundant food, they grew
proportionally more rapidly in the following months, so that at the end
of the fifth month they had reached the same length as their brethren
in the sea, viz. a length of 65 to 70 millimetres.

[16] Ray Lankester considers it to be a portion of the long
denticulated cornua of a genus _Eukeraspis_ allied to _Cephalaspis_.

[17] Ekström, Fische in den Scheeren von Mörkö.

[18] Will probably be found.

[19] We distinguish these sub-regions, because their distinction is
justified by other classes of animals; as regards freshwater fishes
their distinctness is even less than that between Europe and Northern
Asia.

[20] Martens (Preuss. Exped. Ostas. Zool. i. p. 356), has already drawn
attention that a Barbel, said to have been obtained by Ida Pfeiffer in
Amboyna (Günth. Fish. vii. p. 123), cannot have come from that locality.

[21] In the following and succeeding lists, those forms which are
peculiar to and exclusively characteristic of, the region, are printed
in italics; the other regions, in which the non-peculiar forms occur,
are mentioned within brackets [].

[22] Lates calcarifer in India as well as Australia.

[23] One species (_Arius thalassinus_) found in Indian and African
rivers.

[24] This species extends from India into East Africa.

[25] We have left out from these considerations the Ariina and
Cyprinodonts, which can pass with impunity through salt water, and are
spread over much larger areas.

[26] Cope has discovered in a tertiary freshwater-deposit at Idaho
an extinct genus of this group, _Diastichus_. He considers this
interesting fact to be strongly suggestive of continuity of territory
of Asia and North America.--“Proc. Am. Phil. Soc. 1873,” p. 55.

[27] Leidy describes a Siluroid (_Pimelodus_) from tertiary
deposits of Wyoming Territory. “Contrib. to the Extinct Vert. Fauna of
the Western Territ. 1873,” p. 193.

[28] The genera peculiar to the Equatorial zone are printed in italics.

[29] Number of species uncertain.

[30] See p. 151, Fig. 67.

[31] See p. 128, Fig. 55.

[32] See p. 104.

[33] See p. 167, Figs. 79, 81.

[34] See p. 136, Fig. 58.

[35] See p. 167, Fig. 78.

[36] The cartilaginous jaws of Sharks shrink at least a third in
drying, and, therefore, cannot be kept at full stretch without tearing.

[37] This exception is a Ray obtained during the “Challenger”
expedition, and said to have been dredged in 565 fathoms.

[38] See pp. 73 and 74, Figs. 35 and 36.

[39] For other illustrations see p. 73, Fig. 35 (palatal view of head);
p. 74, Fig. 36 (pectoral skeleton); p. 141, Fig. 60 (gills); p. 148,
Fig. 65 (lung); p. 151, Fig. 67 (heart); p. 134, Fig. 57 (intestine);
p. 165, Fig. 77 (ovary).

[40] See p. 97, Fig. 41; and p. 152, Fig. 68.

[41] The Acanthopterygians do not form a perfectly natural group,
some heterogeneous elements being mixed up with it. Neither are the
characters, by which it is circumscribed, absolutely distinctive.
In some forms (certain Blennioids) the structure of the fins is
almost the same as in Anacanths; there are some Acanthopterygians, as
_Gerres_, _Pogonias_, which possess coalesced pharyngeals;
and, finally, the presence or absence of a pneumatic duct loses much of
its value as a taxonomic character when we consider that probably in
all fishes a communication between pharynx and air-bladder exists at an
early stage of development.

[42] In this instance, one may entertain reasonable doubts as to the
usefulness of the Pilot to the Shark.

[43] Mackerel, like other marine fishes, birds, and mammals of prey,
follow the shoals of young and adult Clupeoids in their periodical
migrations; on the British coasts it is principally the fry of the
Pilchard and Sprat which wanders from the open sea towards the coast,
and guides the movements of the Mackerel.

[44] The systematic affinities of these extinct genera are very
obscure. Cope places them, with others (for instance _Protosphyræna_,
which has a sword-like prolongation of the ethmoid), in a distinct
family, _Saurodontidæ_: see “Vertebrata of the Cretaceous Formations of
the West,” 1875.

[45] For specific characters and detailed descriptions we refer to
Günther, “Catal. of Fishes,” vol. vi.

[46] The names “Bull-trout” and “Peal” are not attributable to definite
species. We have examined specimens of _S. salar_, _S. trutta_, and
_S. cambricus_ and _S. fario_, to which the name “Bull-trout” had been
given; and that of “Peal” is given indiscriminately to Salmon-grilse
and to _S. cambricus_.

[47] Fig. 317 is taken from a specimen in which the horny covers of the
dentition were lost, hence it does not represent accurately the shape
of the teeth.

[48] This name is two years older than _Amphioxus_.


Transcriber’s Notes:

1. Obvious printers’, punctuation and spelling errors have been
corrected silently.

2. Where hyphenation is in doubt, it has been retained as in the
original.

3. Some hyphenated and non-hyphenated versions of the same words have
been retained as in the original.

4. Superscripts are represented using the caret character, e.g. D^r. or
X^{xx}.

5. Italics are shown as _xxx_.

6. Bold print is shown as =xxx=.