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  THE LAST LINK

  OUR PRESENT KNOWLEDGE OF THE
  DESCENT OF MAN

  BY

  ERNST HAECKEL
  (JENA)

  WITH NOTES AND BIOGRAPHICAL SKETCHES

  BY

  HANS GADOW, F.R.S.
  (CAMBRIDGE)


  LONDON
  ADAM AND CHARLES BLACK
  1898



CONTENTS


                                                    PAGE
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    INTRODUCTORY                                       1

    COMPARATIVE ANATOMY                                8

    PALÆONTOLOGY                                      20

    OTHER EVIDENCE                                    42

    STAGES RECAPITULATED                              47

 BIOGRAPHICAL SKETCHES:

    LAMARCK, SAINT-HILAIRE, CUVIER, BAER,
    MUELLER, VIRCHOW, COPE, KOELLIKER, GEGENBAUR,
    HAECKEL                                           80

 THEORY OF CELLS                                     115

 FACTORS OF EVOLUTION                                117

 GEOLOGICAL TIME AND EVOLUTION                       135



  NOTE


The address I delivered on August 26 at the Fourth International
Congress of Zoology at Cambridge, 'On our Present Knowledge of the
Descent of Man,' has, I find, from the high significance of the theme
and the general importance of the questions connected with it, excited
much interest, and has led to requests for its publication. Hence this
volume, edited by my friend Dr. H. Gadow, my pupil in earlier days,
who has not only revised the text, but has also enriched it by many
valuable additions and notes.

    ERNST HAECKEL.

_Jena, December, 1898._




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At the end of the nineteenth century, the age of 'natural science,' the
department of knowledge that has made most progress is zoology. From
zoology has arisen the study of transformism, which now dominates the
whole of biology. Lamarck[1] laid its foundation in 1809, and forty
years ago Charles Darwin obtained for it a recognition which is now
universal. It is not my task to repeat the well-known principles of
Darwinism. I am not concerned to explain the scientific value of the
whole theory of descent. The whole of our biological study is pervaded
by it. No general problem in zoology and botany, in anatomy and
physiology, can be discussed without the question arising, How has this
problem originated? What are the real causes of its development?

  [1] See note, p. 80.

This question was almost unknown seventy years ago, when Charles
Darwin, the great reformer of biology, began his academical career at
Cambridge as a student of theology. In the same year, 1828, Carl Ernst
von Baer[2] published in Germany his classical work on the embryology
of animals, the first successful attempt to elucidate by 'observation
and reflection' the mysterious origin of the animal body from the
egg, and to explain in every respect the 'history of the growing
individuality.' Darwin at that time had no knowledge of this great
advance, and he could not divine that forty years later embryology
would be one of the strongest supports of his own life's work--of that
very theory of transformism which, founded by Lamarck in the year of
Darwin's birth, was accepted with enthusiasm by Charles's grandfather
Erasmus. There is no doubt that of all the celebrated naturalists of
the nineteenth century Darwin achieved the greatest success, and we
should be justified in designating the last forty years as the Age of
Darwin.

  [2] See note, p. 89.

In searching for the causes of this unexampled success, we must clearly
separate three sets of considerations: first, the comprehensive reform
of Lamarck's transformism, and its firm establishment by the many
arguments drawn from modern biology; secondly, the construction of the
new theory of selection, as established by Darwin, and independently
by Alfred Wallace (a theory called Darwinism in the proper sense);
thirdly, the deduction of anthropogeny, that most important conclusion
of the theory of descent, the value of which far surpasses all the
other truths in evolution.

It is the third point of Darwin's theory that I shall discuss here; and
I shall discuss it chiefly with the intention of examining critically
the evidence and the different conclusions which at present represent
our scientific knowledge of the descent of man and of the different
stages of his animal pedigree.

It is now generally admitted that this problem is the most important
of all biological questions. Huxley was right when in 1863 he called
it the question of questions for mankind. The problem which underlies
all others, and is more deeply interesting than any other, is as
to the place which man occupies in nature and his relations to the
universe of things. 'Whence our race has come; what are the limits of
our power over nature, and of nature's power over us; to what goal are
we tending--these are the problems which present themselves anew and
with undiminished interest to every man born into the world.' This
impressive view was explained by Huxley thirty-five years ago in his
three celebrated essays on 'Evidence as to Man's Place in Nature.' The
first is entitled 'On the Natural History of the Man-like Apes'; the
second, 'On the Relations of Man to the Lower Animals'; the third, 'On
some Fossil Remains of Man.' Darwin himself felt the burden of these
problems as much as Huxley; but in his chief work, 'On the Origin of
Species,' in 1859, he had purposely only just touched them, suggesting
that the theory of descent would shed light upon the origin of man and
his history. Twelve years later, in his celebrated work on 'The Descent
of Man, and Selection in Relation to Sex,' Darwin discussed fully and
ingeniously all the different sides of this 'question of questions'
from the morphological, historical, physiological, and psychological
points of view. As early as 1866 I myself had applied in the _Generelle
Morphologie der Organismen_ the theory of transformism to anthropology,
and had shown that the fundamental law of biogeny claims the same
value for man as for all the other animals. The intimate causal
connection between ontogeny and phylogeny, between the development of
the individual and the history of its ancestors, enables us to gain
a safe and certain knowledge of our ancestral series. I had at that
time distinguished in this series ten chief degrees of vertebrate
organization. I attributed the highest importance to the logical
connection of anthropogeny with transformism. If the latter be true,
the truth of the former is absolute. 'Our theory that man is descended
from lower vertebrates, and immediately from apes or primates, is a
case of special _deduction_ which follows with absolute certainty from
the general _induction_ of the theory of descent.' The full proof and
detailed explanation of this view was afterwards given in my 'History
of Natural Creation,' and especially in my 'Anthropogeny.'[3] Lastly,
it has received an ample scientific and critical foundation in the
third part of my 'Systematic Phylogeny.'[3]

  [3] See notes, pp. 102, 106

During the forty years which have elapsed since Darwin's first
publication of his theories an enormous literature, discussing the
_general problems_ of transformism as well as its special application
to man, has been published. In spite of the wide divergence of the
different views, all agree in one main point: the natural development
of man cannot be separated from general transformism. There are only
two possibilities. Either all the various species of animals and
plants have been created independently by supernatural forces (and
in this case the creation of man also is a miracle); or the species
have been produced in a natural way by transmutation, by adaptation
and progressive heredity (and in this case man also is descended from
other vertebrates, and immediately from a series of primates). We are
absolutely convinced that only the latter theory is fully scientific.
To prove its truth, we have to examine critically the strength of the
different arguments claimed for it.




  I.


First, we have to consider the relative place which comparative
anatomy concedes to man in the 'natural system' of animals, for the
true value of our 'natural classification' is based upon its meaning
as a pedigree. All the minor and major groups of the system--the
classes, legions, orders, families, genera, and species--are only
different branches of the same pedigree. For man himself, his place
in the pedigree has been fixed since Lamarck,[4] in 1801, defined the
group of vertebrates. The most perfect[5] of these are the Mammalia;
and at the head of this class stands the order of Primates, in which
Linnæus, in 1735, united four 'genera'--Homo, Simia, Lemur, and
Vespertilio. If we exclude the last-named, the Chiroptera of modern
zoology, there remain three natural groups of Primates--the Lemures,
the Simiæ, and the Anthropi or Hominidæ. This is the classification of
the majority of zoologists; but if we compare man with the two chief
groups of monkeys--the Eastern monkeys (or Catarrhinæ) and the Western
or American monkeys (Platyrrhinæ)--there can be no doubt that the
former group is much more closely related to man than is the latter.
In the natural order of the Catarrhinæ we find united a long series
of lower and higher forms. The lowest, the Cynopitheci, appear still
closely related to the Platyrrhinæ and to the Lemures; while, on the
other hand, the tailless apes (Anthropomorphæ) approach man through
their higher organization. Hence one of our best authorities on the
Primates, Robert Hartmann,[6] proposed to subdivide the whole order of
the Simiæ into three groups: (1) Primarii, man together with the other
Anthropomorphæ, or tailless apes; (2) Simiæ, all the other monkeys; (3)
Prosimiæ, or Lemurs. This arrangement has received strong support from
the interesting discovery by Selenka that the peculiar placentation
of the human embryo is the same as in the great apes, and different
from that of all the other monkeys. Our choice between these different
classifications of Primates is best determined by the important thesis
of Huxley, in which, in 1863, he carried out a most careful and
critical comparison of all the anatomical gradations within this order.
In my opinion, this ingenious thesis--which I have called the Huxleyan
Law, or the 'Pithecometra-thesis of Huxley'--is of the utmost value.
It runs as follows: 'Thus, whatever system of organs be studied, the
comparison of their modifications in the ape-series leads to one and
the same result--that the structural differences which separate man
from the gorilla and the chimpanzee are not so great as those which
separate the gorilla from the lower apes.' If we accept the Huxleyan
law without prejudice, and apply it to the natural classification of
the Primates, we must concede that man's place is within the order
of the Simiæ. On examining this relation with care, and judging
with logical persistence, we may even go a step further. Instead of
the wider conception of 'Simiæ,' we must use the restricted term of
Catarrhinæ, and our Pithecometra-thesis has then to be formulated
as follows: _The comparative anatomy of all organs of the group of
Catarrhine Simiæ leads to the result that the morphological differences
between man and the great apes are not so great as are those between
the man-like apes and the lowest Catarrhinæ_. In fact, it is very
difficult to show why man should not be classed with the large apes in
the same zoological family. We all know a man from an ape; but it is
quite another thing to find differences which are absolute and not of
degree only. Speaking generally, we may say that man alone combines the
four following features: (1) Erect walk; (2) extremities differentiated
accordingly; (3) articulate speech; (4) higher reasoning power. Speech
and reason are obviously relative distinctions only--the direct result
of more brains and more brain-power, the so-called mental faculties.
The erect walk is not an absolutely distinguishing characteristic: the
large apes likewise walk on their feet only, supporting their bodies
by touching the ground with the backs of their hands--in fact, with
their knuckles--and this is a mode of progression very different from
that of the tailed monkeys, which walk upon the palms of their hands.
There are, however, two obvious differences in the development of the
muscles. In man alone the gastrocnemius and the soleus muscle are thick
enough to form the calf of the leg, and the glutæus maximus is enlarged
into the buttocks. A fourth glutæal muscle occurs occasionally in
man, while it is constantly present in apes as the so-called musculus
scansorius. Concerning the muscles of the whole body, we cannot do
better than quote Testut's summary: 'The mass of recorded observations
upon the muscular anomalies in man is so great, and the agreement of
many of these with the condition normal in apes is so marked, that the
gap which usually separates the muscular system of man from that of the
apes appears to be completely bridged over.'

  [4] See note, p. 80.

  [5] _Perfect_, in the sense of highest stage of evolution, may seem a
  _petitio principii_. Leaving aside the consideration that no living
  creature is absolutely perfect, in the sense that its organization
  cannot become more efficient or proficient, we have here to deal with
  relative perfection of the whole organization. A fish or a snake is in
  its way more specialized than a mammal; but specialization does not
  necessarily mean height of development: it generally means life in a
  comparatively narrow groove. The acts of giving birth and nourishing
  the young with the mother's milk is a much higher stage than the act
  of laying eggs and letting them run their chance. The development of
  a hairy coat goes along with heightened temperature of the blood,
  subsequent greater independence of the surrounding temperature, and
  increased steady activity of the brain and other nerve-centres. The
  brain of the Mammalia, in its minute structure, is much more complex.
  This rule applies to some of the principal sense organs, chiefly the
  nose and the ear. The skeleton, not so much as a whole as in the
  various bones and joints, is more neatly finished, and built up more
  in conformity with 'scientific principles,' than is the case even with
  birds, in spite of their marvellous specialization. The same is the
  case with the vascular system, notably the heart and the veins, and
  with the excretory organs. In all of these many imperfections, still
  to be found in the other classes, have been corrected in Mammalia. The
  Primates take an easy first by their hands, and among them the apes and
  man himself by their brains.

  [6] 'Die menschenähnlichen Affen und ihre Organisation im Vergleich zur
  menschlichen.' 1883.

There are, for example, the muscles of the ear. In most people the
majority, or even all of them, are no longer movable at will, while in
the apes they are still in use. The important point, however, is that
these muscles are still present in man, although often in a reduced
condition. They are the following: (1) Musculus auricularis anterior
or attrahens auris, which is frequently much reduced and no longer
reaches the ear at all, being then absolutely useless; (2) Musculus
auricularis superior or attollens auris, more constant than the former;
(3) Musculus auricularis posterior or retrahens auris, likewise often
functional. Occasionally smaller slips differentiated from these
three muscles are present, and as so-called intrinsic muscles are
restricted to the ear itself; their function is, or was, that of
curling up or opening the external ear.

[Illustration: OUTLINES OF THE LEFT EAR OF--

1. _Lemur macaco_; 2. _Macacus rhesus_, the Rhesus monkey; 3.
Cercopithecus, a macaque; 4. human embryo of six months; 5. man, with
Darwin's point well retained: the dotted outline is that of the ear of
a baboon; 6. orang-utan (after G. Schwalbe):[7] ^x the original tip of
the ear; 7. human ear with the principal muscles.

  [7] G. Schwalbe, 'In wiefern ist die menschliche Ohrmuschel ein
  rudimentäres Organ?'--In what Respects is the Human Outer Ear a
  Rudimentary Organ? (_Archiv f. Anatomie und Physiologie_, 1889).]

In connection with the ear, I may touch upon another interesting
and most suggestive little feature which is present in many
individuals--namely, 'Darwin's point.' This is the last remnant of the
original tip of the ear, before the outer, upper, and hinder rim became
doubled up or folded in. It is a feature quite useless, and absolutely
impossible of interpretation, excepting as the vestige of such previous
ancestral conditions as are normal in the monkeys.

In some cases the reduction of muscles has proceeded further in apes
than in man--for example, the muscles of the little toe. Another
instance is afforded by the coccyx or vestige of the tail; this is
still furnished with muscles which are now in man, as well as in
the apes, quite useless, and vary considerably with every sign of
degeneration, most so in the orang-utan.

Darwin has mentioned the frequent action of the 'snarling muscle,' by
which, in sneering, our upper canine teeth are exposed, like those of a
dog prepared to fight.

Monkeys and apes possess vocal sacs, especially large in the
orang-utan; survivals of them, although no longer used, persist in man
in the shape of a pair of small diverticula, the pouches of Morgagni,
between the true and the false vocal cords.

'In the native Australians, the dental formula appears least removed
from the hypothetical original type, for in it are still found complete
rows of splendid teeth, with powerfully-developed canines and molars,
the latter being either uniform, or even increasing in size, as we
proceed backwards, in such a way that the wisdom tooth is the largest
of the series. This is decidedly a pithecoid characteristic which is
always found in apes. The upper incisors of the Malay, apart from their
prognathous disposition, have occasionally a distinctly pithecoid
form, their anterior surface being convex, and their lingual surface
slightly concave. The ancestors of Europeans seem to have had the same
form of teeth, for the oldest existing fragments of skulls from the
Mammoth age (_e.g._, the jaws from La Naulette, in Belgium) reveal
tooth-forms which must be classed with those of the lowest races of
to-day.'[8]

  [8] Wiedersheim, 'Der Bau des Menschen als Zeugniss für seine
  Vergangenheit.' Freiburg, 1888. Translated: 'The Structure of Man an
  Index to his Past History.' London, 1895.

Now we are able to apply this fundamental Pithecometra-thesis directly
to the classification of the Primates and to the phylogeny of man,
which is intimately connected with it, because in this order, as in
all the other groups of animals, the natural system is the clear
expression of true phylogenetic affinity. Four results follow from our
thesis: (1) The Primates, as the highest legion or order of mammals,
form one natural, monophyletic group. All the Lemures, Simiæ, and
Homines descend from one common ancestral form, from a hypothetical
'Archiprimas.' (2) The Lemures are the older and lower of the natural
groups of the Primates; they stand between the oldest Placentalia
(Prochoriata) and the true Simiæ. (3) All the Catarrhinæ, or Eastern
Simiæ, form one natural monophyletic group. Their hypothetical
common ancestor, the Archipithecus, may have descended directly or
indirectly from a branch of the Lemures. (4) Man is descended directly
from one series of extinct Catarrhine ancestors. The more recent
ancestors of this series were tailless anthropoids (similar to the
Anthropopithecus), with five sacral vertebræ. The more remote ancestors
were tailed Cercopitheci, with three or four sacral vertebræ.

These four theses possess, in my opinion, absolute certainty.
They are independent of all future anatomical, embryological, and
palæontological discoveries which may possibly throw more light upon
the details of our phyletic anthropogenesis.




  II.


The next question is, how the facts of palæontology agree with these
most important results of comparative anatomy and ontogeny. The fossils
are the true historical 'medals of creation,' the palpable evidence of
the historical succession of all those innumerable organic forms which
have peopled the globe for many millions of years. Here the question
arises, If the known fossil specimens of Mammalia, and particularly
of Primates, give proof of these Pithecometra-theses, do they confirm
directly the descent of man from ape-like creatures? The answer to this
question is, in my opinion, affirmative.

It is true that the gaps in the palæontological evidence, here as
elsewhere, are many and keenly felt. In the order of the Primates
they are greater than in many other orders, chiefly because of the
arboreal life of our ancestors. The explanation is very simple. It is
really due to a long chain of favourable coincidences if the skeleton
of a vertebrate, covered as it was with flesh and skin, and containing
still more perishable viscera, is petrified at all. The body may be
devoured by other creatures, and its bones scattered about; or it rots
away and crumbles to pieces. Many animals hide in thick undergrowth
when death approaches them; and, leading an almost entirely arboreal
life, the Primates are especially likely to disappear without being
fossilized. It is only when the body is quickly covered with sand, or
is embedded in suitable lime or silica containing mud, that the process
of petrifaction can come to pass. Even then it is only by great good
luck that we come across such a fossil. Very few countries have been
searched systematically, and the areas that have been searched amount
to little in comparison with the whole surface of the land, even if we
leave out of account the fact that more than two-thirds of the globe
are covered by water.

These deplorable deficiencies of empirical palæontology are balanced
on the other side by a growing number of positive facts, which possess
an inestimable value in human phylogeny. The most interesting and most
important of these is the celebrated fossil _Pithecanthropus erectus_,
discovered in Java in 1894 by Dr. Eugène Dubois.[9] Three years ago
this now famous ape-like man provoked an animated discussion at the
third International Zoological Congress at Leyden. I may therefore
be allowed to say a few words as to its scientific significance.
Unfortunately, the fossil remains of this creature are very scanty: the
skull-cap, a femur, and two teeth. It is obviously impossible to form
from these scanty remains a complete and satisfactory reconstruction of
this remarkable Pliocene Primate.

[9] _Pithecanthropus erectus._ 'Eine menschenähnliche Uebergangsform
aus Java' ('A Human-like Transitional Form'). Batavia, 1894.

The more important points are the following: The remains in question
rested upon a conglomerate which lies upon a bed of marine marl and
sand of Pliocene age. Together with the bones of Pithecanthropus were
found those of Stegodon, Leptobos, Rhinoceros, Sus, Felis, Hyæna,
Hippopotamus, Tapir, Elephas, and a gigantic Pangolin. It is remarkable
that the first two of these genera are now extinct, and that neither
hippopotamus nor hyæna exists any longer in the Oriental region. If we
may judge from these fossil remains, the bones of Pithecanthropus are
not younger than the oldest Pleistocene, and probably belong to the
upper Pliocene. The teeth are like those of man. The femur, also, is
very human, but shows some resemblances to that of the gibbons. Its
size, however, indicates an animal which stood when erect not less
than 5 feet 6 inches high. The skull-cap also is very human, but with
very prominent eyebrow ridges, like those of the famous Neanderthal
cranium. It is certainly not that of an idiot. It had an estimated
cranial capacity of about 1,000 cubic centimetres--that is to say, much
more than that of the largest ape, which possesses not more than 600
c.c. The crania of female Australians and Veddahs measure not more than
1,100, some even less than 1,000 c.c.; but, as these Veddah women stand
only about 4 feet 9 inches high, the computed cranial capacity of the
much taller Pithecanthropus is comparatively very low indeed.[10]

  [10] On the day after the delivery of this address Dr. Dubois exhibited
  the cranium of Pithecanthropus, from which he had removed the stony
  matrix which filled the inside, in order to examine the impression left
  by the cerebral convolutions. He was able to show that they also are
  very human, and more highly developed than those of the recent apes. [
  Illustration: The upper figure represents the outlines
  of the skull of Pithecanthropus, as restored by Manouvier.[11] The
  lower figure shows the comparative size and shape of Pithecanthropus,
  the Neanderthal skull, a specimen of the Cro-Magnon race of neolithic
  France, and a Young Chimpanzee before the full development of the
  supraorbital crests.]

  [11] L. Manouvier: 'Deuxième étude sur le Pithecanthropus erectus comme
  précurseur présumé de l'homme.' (_Bulletins de la Soc. d'Anthropologie
  de Paris_, 1895.)

The final result of the long discussion at Leyden was that, of twelve
experts present, three held that the fossil remains belonged to a low
race of man; three declared them to be those of a man-like ape of great
size; the rest maintained that they belonged to an intermediate
form, which directly connected primitive man with the anthropoid
apes. This last view is the right one, and accords with the laws of
logical inference. _Pithecanthropus erectus_ of Dubois is truly a
Pliocene remainder of that famous group of highest Catarrhines which
were the immediate pithecoid ancestors of man. He is, indeed, the
long-searched-for 'missing link,' for which, in 1866, I myself had
proposed the hypothetical genus Pithecanthropus, species Alalus.

It must, however, be admitted that this opinion is still strongly
combated by some distinguished authorities. At the Leyden Congress it
was attacked by the illustrious pathologist Rudolf Virchow.[12] He,
however, is one of the minority of leading men of science who set
themselves to refute the theory of Evolution in every possible way. For
thirty years he has defended the thesis: 'It is quite certain that man
is not a descendant of apes.' He declares any intermediate form to be
unimaginable save in a dream.

  [12] See Notes, p. 93.

Virchow went to the Leyden Congress with the set purpose of disproving
that the bones found by Dubois belonged to a creature which linked
together apes and man. First, he maintained that the skull was that
of an ape, while the thigh belonged to man. This insinuation was at
once refuted by the expert palæontologists, who declared that without
the slightest doubt the bones belonged to one and the same individual.
Next, Virchow explained that certain exostoses or growths observable on
the thigh proved its human nature, since only under careful treatment
the patient could have healed the original injury. Thereupon Professor
Marsh, the celebrated palæontologist, exhibited a number of thigh-bones
of wild monkeys which showed similar exostoses and had healed without
hospital treatment. As a last argument the Berlin pathologist declared
that the deep constriction behind the upper margin of the orbits
proved that the skull was that of an ape, as such never occurred in
man. It so happened that a few weeks later Professor Nehring of Berlin
demonstrated exactly the same formation on a human prehistoric skull
received by him from Santos, in Brazil.

Virchow was, in fact, just as unlucky in Leyden in his fight with our
pliocene ancestor as he had been unfortunate in his opinion on the
famous skulls of Neanderthal, Spy, La Naulette, etc., every one of which
he explained as a pathological abnormality. It would be a very curious
coincidence indeed if all these and other fossil human remains were
those of idiots or otherwise abnormal individuals, provided they are
old and low enough in their organization to be of phylogenetic value to
the unbiassed zoologist.

As the sworn adversary of Evolution, transformism, and Darwinism in
particular, but a believer in the constancy of species, the great and
renowned pathologist has been driven to the incredible contention that
all variations of organic forms are pathological.

Four years ago, as honorary president of the Anthropological Congress
at Vienna, he attacked Darwinism in the severest manner, and declared
that 'man may be as well descended from the elephant or from the sheep
as from the ape.' Such attacks on the theory of transformism indicate a
failure to understand the principles of the theory of Evolution and to
appreciate the significance of palæontology, comparative anatomy, and
ontogeny.

The thousands of other objections which have been made during the last
forty years (chiefly by outsiders) may be passed over in silence. They
do not require serious refutation. In spite of, or perhaps because of,
these attacks, the theory of Evolution stands established more firmly
than ever.

It is easy for the outsider to exult over the difficulties which our
problem implies--difficulties which we who have given our lives to the
study understand likewise, and try our best not only to bridge over,
but also to point out. Anyhow, we do not conceal them; while those who
reject the explanation offered by Evolution make the most of the gaps,
and pass silently over the far more numerous points favourable to our
theory.

How fruitful during the last thirty years the astonishing progress in
our palæontological knowledge has been for our Pithecometra-thesis is
best shown by a short glance at the growth of our knowledge of fossil
Primates. Cuvier,[13] the founder of palæontology, continued up to the
time of his death, in 1832, to assert that fossil remains of monkeys
and lemurs did not exist. The only skull of a fossil lemuroid which
he described (namely, Adapis) he declared to be that of an ungulate.
Not until 1836 were the first fragments of extinct monkeys found in
India; it was two years later, near Athens, that the skeleton of
_Mesopithecus penthelicus_ was discovered. Other remains of lemurs were
found in 1862. But during the last twenty years the number of fossil
Primates has been augmented by the remarkable discoveries of Gaudry,
Filhol, Milne Edwards, Seeley, Schlosser, and others in Europe; of
Marsh, Cope, Osborn, Leidy, Ameghino, in South America; and Forsyth
Major in Madagascar.[14] These tertiary remains, chiefly of Eocene and
Miocene date, fill many gaps between existing genera of Primates, and
afford us quite a clear insight into the phyletic development of this
order during the millions of years of the Cænozoic age.

  [13] See notes, p. 87.

  [14]
   F. AMEGHINO: 'Contribucion al conocimiento de los mamíferos
   de la república Argentina.' In _Actas de la Academia nacional de
   Sciencias en Cordoba_, 1889.--Another article in _Revista Argentina de
   Historia natural_. Buenos Aires, 1891.

   A. GAUDRY: 'Animaux fossiles et géologie de l'Attique.'
   1862.--'Le Dryopithèque.' _Mém. Soc. géol. de France_:
   'Paléontologie.' 1890.

   O. MARSH: 'Introduction and Succession of Vertebrate Life in
   America.' Address, Amer. Assoc. Adv. Sci., Nashville, 1887.

   H. F. OSBORN: 'The Rise of the Mammalia in North America.'
   Address, Amer. Assoc. Adv. Sci., Madison, 1893.

   L. RUETIMEYER: 'Ueber die Herkunft unserer Thierwelt,' Basel,
   1867.

   C. S. FORSYTH MAJOR: 'Fossil Monkeys from Madagascar.'
   _Geological Magazine_, 1896.

   M. SCHLOSSER: 'Ueber die Beziehungen der ausgestorbenen
   Saeugethierfaunen und ihr Verhaeltniss zur Saeugethierfauna der
   Gegenwart.' Biolog. Centralblatt, 1888.

The most important difference between the two groups of existing
monkeys is indicated by their dentition. Adult man possesses, like
all the other Catarrhine Simiæ, thirty-two teeth, whilst the American
monkeys (the Platyrrhinæ) have thirty-six teeth--namely, one pair of
premolars more in the upper and lower jaws. Comparative odontology
leads us to the phylogenetic conclusion that this number has been
produced by reduction from a still older form with forty-four teeth.
This typical dental formula (three incisors, one canine, four
premolars, and three molars, in each half-jaw) is common to all those
most important older mammals which in the beginning of the Eocene
period constituted the four large groups of Lemuravida, Condylarthra,
Esthonychida, and Ictopsida. These are the four ancestral groups
of the four main orders of Placentalia--namely, of the Primates,
Ungulata, Rodentia, and Carnassia. They seem to be so closely related
by their primitive organization that they may be united in one common
super-order, Prochoriata.

With a considerable degree of probability, we are led to formulate
the further hypothesis that all the orders of Placentalia--from the
lowest Prochoriata upwards to man--have descended from some unknown
common ancestor living in the Cretaceous period, and that this oldest
placental form originated from some Jurassic group of marsupials.

Among these numerous fossil Lemures which have been discovered within
the last twenty years, there exist, indeed, all the connecting forms
of the older series of Primates, all the 'missing links' sought for by
comparative odontology.

The oldest Lemures of the tertiary age are the Eocene Pachylemures,
or Hyopsodina. They possess the complete dentition of the
Prochoriata--namely, forty-four teeth (3.1.4.3/3.1.4.3). Then follow
the Eocene Palæolemures, or Adapida, with forty teeth, they having lost
one pair of incisors in each jaw. To these are attached the younger
Autolemures, or Stenopida, with thirty-six teeth, they thus possessing
already the same dentition as the Platyrrhinæ. The characteristic
dentition of the Catarrhinæ is derived from this formula by the loss of
another premolar.

These relations are so clear and so closely connected with a
gradual transformation of the whole skull, and with the progressive
differentiation of the Primate-form, that we are justified in saying
that the pedigree of the Primates, from the oldest Eocene Lemures
upwards to man, is now so well known, its principal features so firmly
fixed within the Tertiary age, that there is no missing link whatever.

Quite different, and much more incomplete, is the palæontological
evidence, if we go further back into the Secondary or Mesozoic age,
and look there for the older ancestors of the mammalian series. There
we meet everywhere with wide gaps, and the scarce fragments of fossil
Mesozoic mammals (excessively rare in the Cretaceous formation) are too
poor to permit definite conclusions as to their systematic position.
Indeed, comparative anatomy and ontogeny lead us to the hypothesis
that the oldest Cretaceous Mammalia--the Prochoriata--are descended
from Jurassic marsupials, and these again from Monotremes. We may
also suppose with high probability that among the unknown Cretaceous
Prochoriata there have been Lemuravida and forms intermediate between
these and the Jurassic Amphitheriidæ, and that these marsupials in
their turn are descendants of Pantotheria or similar monotreme-like
creatures of the Triassic age. Any certain evidence for these
hypotheses is at present still wanting. One important fact, however,
is established--namely, that these interesting and oldest Mammalia--the
Pantotheria of Marsh, the Triassic Dromatheriidæ, and the Jurassic
Triconodontidæ of Osborn--were small insectivorous mammals with a very
primitive organization. Probably they were Monotremes, and may be
derived directly from Permian Sauromammalia, an ill-defined mixture of
Mammalia and Reptilia.

This generalized characteristic supports our view that _the whole
class of Mammalia is monophyletic_, and that all its members, from
the oldest Monotremes upwards to man, have descended from one common
ancestor living in the older Triassic, or perhaps in the Permian,
age. To acquire full conviction of this important conception, we have
only to think of the hair and the glands of our human skin, of our
diaphragm, the heart and the blood corpuscles without a nucleus, our
skull with its squamoso-mandibular articulation. All these singular
and striking modifications of the vertebrate organization are common
to mammals, and distinguish them clearly from the other Craniota. This
characteristic combination and correlation proves that they have been
developed only _once_ in the history of the vertebrate stem, and that
they have been transferred by heredity from one common ancestor to all
the members of the class of Mammalia.

The next step, as we trace our human phylogeny to its origin, leads us
further back into the lower Vertebrata, into that obscure Palæozoic
age the immeasurable length of which (much greater than that of the
Mesozoic) may, according to one of the newest geological calculations,
have comprised about one thousand millions of years.[15]

  [15] See note, 'Geological Time and Evolution' p. 134.

The first important fact we have to face here is the complete absence
of mammalian remains. Instead of these we find in the later Palæozoic
period, the Permian, air-breathing _reptiles_ as the earliest
representatives of Amniota. They belong to the most primitive order
of that class, the Tocosauria; and besides them there were the
Theromorpha, which approach the Mammalia in a remarkable manner. These
reptiles in turn were preceded, in the Carboniferous period, by true
Amphibia, most of them belonging to the armour-clad Stegocephali.
These interesting Progonamphibia were the oldest Tetrapoda, the first
vertebrates which had adapted themselves to the terrestrial mode of
life; in them the swimming fin of fishes and Dipneusta was transformed
into the pentadactyle extremities characteristic of quadrupeds.

To appreciate the high importance of this metamorphosis, we need only
compare the skeleton of our own human limbs with that of the living
Amphibia. We find in the latter the same characteristic composition as
in man: the same shoulder and pelvic girdle; the same single bone, the
humerus or the femur, followed by the same pair of bones in the forearm
and leg; then the same skeletal elements composing the wrist and the
ankle regions; and, lastly, the same five fingers and toes.

The arrangement of these bones, peculiar and often complicated, but
everywhere essentially the same in all the Tetrapoda, is a striking
evidence that man is a descendant from the oldest pentadactyle Amphibia
of the Carboniferous period. In man the pentadactyle type has been
better preserved by constant heredity than in many other Mammalia,
notably the Ungulata.

The oldest Carboniferous Amphibia, the armour-clad Stegocephali, and
especially the remarkable Branchiosauri discovered by Credner, are
now regarded by all competent zoologists as the indubitable common
ancestral group of all Tetrapoda, comprising both Amphibia and Amniota.
But whence this most remote group of Tetrapoda? That difficult question
is answered by the marvellous progress of modern palæontology, and
the answer is in complete harmony with the older results arrived
at by comparative anatomy and ontogeny. Thirty-four years ago Carl
Gegenbaur,[16] the great living master of comparative anatomy, had
demonstrated in a series of works how the skeletal parts of the various
classes of Vertebrata, especially the skull and the limbs, still
represent a continuous scale of phyletic gradations. Apart from the
Cyclostomes, there are the fishes, and among them the Elasmobranchi
(sharks and rays), which have best preserved the original structure in
all its essential parts of organization. Closely connected with the
Elasmobranchi are the Crossopterygii, and with these the Dipneusta or
Dipnoi. Among the latter the highest importance attaches to the ancient
Australian Ceratodus. Its organization and development is now, at last,
becoming well known. This transitional group of Dipnoi, 'fishes with
lungs' but without pentadactyle limbs, is the morphological bridge
which joins the Ganoids and the oldest Amphibia. With this chain
of successive groups of Vertebrata, constructed anatomically, the
palæontological facts agree most satisfactorily. Selachians and Ganoids
existed in the Silurian times, Dipnoi in the Devonian, Amphibia in the
Carboniferous, Reptilia in the Permian, Mammalia in the Trias. These
are historical facts of first rank. They connote in the most convincing
manner that remarkable ascending scale in the series of vertebrates
for our knowledge of which we are indebted to the works of Cuvier and
Blainville, Meckel, Johannes Mueller and Gegenbaur, Owen and Huxley.
The historical succession of the classes and orders of the Vertebrata
in the course of untold millions of years is definitely fixed by the
concordance of those leading works, and this invaluable acquisition is
much more important for the foundation of our human pedigree than would
be a complete series of all possible skeletons of Primates.

  [16] See note, p. 97.

Greater and more frequent difficulties arise if we penetrate further
into the most remote part of the human phylogeny, and attempt to derive
the vertebrate stem from an older stem of invertebrate ancestors. None
of those had a skeleton which could be petrified; and the same remark
applies to the lowest classes of Vertebrata--to the Cyclostomes and
the Acrania. Palæontology, therefore, can tell us nothing about them;
and we are limited to the other two great documents of phylogeny--the
results of comparative anatomy and ontogeny. The value of their
evidence is, however, so great that every competent zoologist can
perceive the most important features of the most remote portion of our
phylogeny.

Here the first place belongs to the invaluable results which modern
comparative ontogeny has gained by the aid of the biogenetic law or
the theory of recapitulation. The foundation-stones of vertebrate
embryology had been laid by the works of Von Baer, Bischoff,[17] Remak,
and Koelliker;[18] but the clearest light was thrown upon it by the
famous discoveries of Kowalevsky[19] in 1866. He proved the identity
of the first developmental stages of Amphioxus and the Ascidians, and
thereby confirmed the divination of Goodsir, who had already announced
the close affinity of Vertebrates and Tunicates. The acknowledgment of
this affinity has proved of increasing importance, and has abolished
the erroneous hypothesis that the Vertebrata may have arisen from
Annelids or from other Articulata. Meanwhile, from 1860 to 1872, I
myself had been studying the development of the Spongiæ, Medusæ,
Siphonophora, and other Coelenterata. Their comparison led me to the
statements embodied in the 'Gastræatheorie,' the first abstract of
which was published in 1872 in my monograph of the Calcispongiæ.

  [17] Wilhelm Bischoff of Munich: works on the history of the
  development of the rabbit, dog, guinea-pig, roe-deer. 1840-1854.

  [18] See note, p. 96.

  [19] 'Ueber die Entwicklung der einfachen Ascidien,' Mém. Acad. St.
  Petersbourg, vii. ser., tome x. (1866). Other papers in 'Archiv f.
  Mikroskop. Anatomie,' vii. (1871); xiii. (1877).

These ideas were carried on and expanded during the subsequent ten
years by the help of many excellent embryologists--first of all by E.
Ray Lankester and Francis Balfour. The most fruitful result of these
widely extended researches was the conclusion that the first stages of
embryonic development are essentially the same in all the different
Metazoa, and that we may derive from these facts certain views on
the common descent of all from one ancestral form. The unicellular
egg[20] repeats the stage of our Protozoan ancestors; the Blastula
is equivalent to an ancestral coenobium of Magosphæra or Volvox;
the Gastrula is the hereditary repetition of the Gastræa, the common
ancestor of all the Metazoa.

  [20] See note, p. 115--Theory of cells.

Man agrees in all these respects with the other vertebrates, and must
have descended with them from the same common root.

Particularly obscure is that part of our phylogeny which extends from
the Gastræa to Amphioxus. The morphological importance of this last
small creature had been perceived by Johannes Mueller, who in 1842
gave the first accurate description of it. It would not, of course, be
correct to proclaim the modern Amphioxus the common ancestor of all the
vertebrates; but he must be regarded as closely related to them, and
as the only survivor of the whole class of Acrania. If the Amphioxidæ
had through some unfortunate accident become extinct, we should not
have been able to gain anything like a positive glimpse at our most
remote vertebrate ancestor. On the one hand, Amphioxus is closely
connected with the early larva of the Cyclostomes, which are the
oldest Craniota, and the pre-Silurian ancestors of the fishes. On the
other hand, the ontogeny of Amphioxus is in harmony with that of the
Ascidians, and if this agreement is not merely coincidental, but due to
relationship, we are justified in reconstructing for both Ascidians
and Amphioxus one common ancestral group of chordate animals, the
hypothetical _Prochordonia_. The modern Copelata give us a remote idea
of their structure. The curious Balanoglossus, the only living form of
Enteropneusta, seems to connect these Prochordonia with the Nemertina
and other Vermalia, which we unite in one large class--Frontonia.

No doubt these pre-Cambrian Vermalia, and the common root of all
Metazoa, the Gastræades, were connected during the Laurentian period
by a long chain of intermediate forms, and probably among these
were some older forms of Rotatoria and Turbellaria; but at present
it is not possible to fill this wide gap with hypotheses that are
satisfactory, and we have to admit that here indeed are many missing
links in the older history of the Invertebrata. Still, every zoologist
who is convinced of the truth of transformism, and is accustomed to
phylogenetic speculations, knows very well that their results are most
unequal, often incomplete.




III.


Let us now recapitulate the ancestral chain of man, as it is set forth
in the accompanying diagram (p. 55), which represents our present
knowledge of our descent. For simplicity's sake the many side-issues
or branches which lead to groups not in the main line of our descent
have been left out, or have been indicated merely. Many of the stages
are of course hypothetical, arrived at by the study of comparative
anatomy and ontogeny; but an example for each of them has been taken
from those living or fossil creatures which seem to be their nearest
representatives.

1. The most remote ancestors of all living organisms were living beings
of the simplest imaginable kind, organisms without organs, like
the still existing _Monera_. Each consisted of a simple granule of
protoplasm, a structureless mass of albuminous matter or plasson, like
the recent Chromaceæ and Bacteriæ. The morphological value of these
beings is not yet that of a cell, but that of a cytode, or cell without
a nucleus. Cytoplasm and nucleus were still undifferentiated.

I assume that the first Monera owe their existence to spontaneous
creation out of so-called anorganic combinations, consisting of carbon,
hydrogen, oxygen, and nitrogen. An explanation of this hypothesis I
have given in my 'Generelle Morphologie.'

The Monera probably arose early in the Laurentian period. The oldest
are the Phytomonera, with vegetable metabolism. They possessed the
power (characteristic of plants) of forming albumin by synthesis from
carbon, water, and ammonia. From some of these plasma-forming Monera
arose the plasmophagous Zoomonera with animal metabolism, living
directly upon the produce of their plasmodomous or plasma-forming
sisters. This is the first instance of the great principle of division
of labour.

2. The second stage is that of the _simple and single cell_, a bit
of protoplasm with a nucleus. Such unicellular organisms are still
very common. The _Amoebæ_ are their simplest representatives. The
morphological value of such beings is the same as that of the egg
of any animal. The naked egg cells of the sponges creep about in an
amoeboid fashion, scarcely distinguishable from Amoeba. The same
remark applies to the egg-cell of man himself in its early stages
before it is enclosed in a membrane. The first unicellular organisms
arose from Monera through differentiation of the inner nucleus from the
outer protoplasm.

3. Repeated division of the unicellular organism produces the
_Synamoebium_, or community of Amoebæ, provided the divisional
products, or new generations of the original cell, do not scatter,
but remain together. The existence of such a _Coenobium_, a number
of equal and only loosely-connected cells, as a separate stage in the
ancestral history of animals, is made highly probable by the fact that
the eggs of all animals undergo after fertilization such a process of
repeated self-division, or 'cleavage,' until the single egg cell is
transformed into a heap of cells closely packed together, not unlike a
mulberry (_morula_)--hence _morula_ stage in ontogeny.

4. The morula of most animals further changes into a _Blastula_, a
hollow ball filled with fluid, the wall being formed by a single layer
of cells, the blastoderm or germinal layer. This modification is
brought about by the action of the cells--they conveying nourishing
fluid into the interior of the whole cell colony and thereby
being themselves forced towards the surface. The Blastula of most
Invertebrata, and even that of Amphioxus, is possessed of fine ciliæ,
or hair-like processes, the vibrating motion of which causes the whole
organism to rotate and advance in the water. Living representatives of
such Blastæads, namely, globular gelatinous colonies of cells enclosing
a cavity, are Volvox and Magosphæra.

5. The Blastula of most animals assumes a new larval form called
_Gastrula_, in which the essential characteristics are that a portion
of the blastoderm by invagination converts the Blastula into a cup
with double walls, enclosing a new cavity, the primitive gut. This
invagination or bulging-in obliterates the original inner cavity of
the Blastula. The outer layer of the Gastrula is the ectoderm, the
inner the endoderm; both pass into each other at the blastoporus, or
opening of the gut cavity. The Gastrula is a stage in the embryonic
development of the various great groups of animals, and some such
primitive form as ancestral to all Metazoa is thus indicated. This
hypothetical _Gastræa_ is still very essentially represented by the
lower Coelenterates--_e.g._, Olynthus, Hydra.

6. The sixth stage--that of the _Platodes_, or flat-worms--is very
hypothetical. They are bilateral gastræads, with a flattened oblong
body, furnished with ciliæ, with a primitive nervous system, simple
sensory and reproductive organs, but still without appendages, body
cavity, vent, and blood-vessels. The nearest living representatives of
such creatures are the acoelous Turbellarians--_e.g._, Convoluta, a
free-swimming, ciliated creature.

7. The next higher stage is represented by such low animals as the
_Gastrotricha_--_e.g._, Chætonotus among the Rotatoria, which differ
from the rhabdocoelous Turbellarians chiefly by the formation of
a vent and the beginnings of a coelom, or cavity, between gut and
body wall. The addition of a primitive vascular system and a pair of
nephridia, or excretory organs, is first met with in the _Nemertines_.

8. These, together with the _Enteropneusta_ (Balanoglossus), are
comprised under the name of Frontonia, or Rhynchelminthes, and form the
highest group of the Vermalia.

The Enteropneusta especially fix our attention, because they alone,
although essentially 'worms,' exhibit certain characteristics which
make it possible to bridge over the gulf which still separates the
Invertebrata from the vertebrate phylum. The anterior portion of the
gut is transformed into a breathing apparatus--hence Gegenbaur's
term of Enteropneusta, or Gut-breathers. Moreover, Balanoglossus and
Cephalodiscus possess another modification of the gut--namely, a
peculiar diverticulum, which, in the present state of our knowledge,
may be looked upon as the forerunner of the chorda dorsalis.

9. Stage of _Prochordonia_, as indicated by the larval form, called
Chordula, which is common to the Tunicata and all the Vertebrata.
These two groups possess three most important features: (_a_) A chorda
dorsalis, a stiff rod lying in the long axis of the body, dorsally from
the gut and below the central nervous system. This latter, for the
first time in the animal kingdom, appears in the shape of a spinal
cord. (_b_) The use of the anterior portion of the gut for respiratory
purposes. (_c_) The larval development of the Tunicata is essentially
the same as that of the Vertebrata in its early stages. Only the
free-swimming Copelata or Appendicularia among the Tunicates retain
most of these features. The others, which become sessile--namely, the
Ascidiæ, or sea-squirts--degenerate and specialize away from the main
line.

10. Stage of the _Acrania_, represented by Amphioxus. The early
development of this little marine creature agrees closely with
that of the Tunicates; but one important feature is added to its
organization--namely, metamerism, segmentally arranged mesoderm.
Amphioxus still possesses neither skull nor vertebræ, neither ribs
nor jaws, and no limbs. But it is a member of the Vertebrata if we
define these as follows: Bilateral symmetrical animals with segmentally
arranged mesoderm, with a chorda dorsalis between the tubular nervous
system and the gut, and with respiratory organs which arise from the
anterior portion of the gut. We do not assume that Amphioxus stands
in the direct ancestral line; it is probably much specialized, partly
degenerated, and represents a side-branch; but it is, nevertheless,
the only creature, hitherto known, which satisfactorily connects the
Vertebrata with their invertebrate ancestors. Many other efforts have
been made to solve the mystery of the origin of the Vertebrata--all
less satisfactory than the present suggestion, or even absolutely
futile. This remark applies especially to the attempts to derive them
from either Articulata or Echinoderms. The other great and highly
developed phylum, the Mollusca, is quite out of the question. We have
to go back to a level at which all these principal phyla meet, and
there we find the Vermalia, the lower of which alone permit connection
in an upward direction with the higher phyla.

    ANCESTRAL TREE OF THE VERTEBRATA.

    _Abridged from 'Systemat. Phylogenie,' § 15._

    Names underlined refer to hypothetical groups.

                                  _Mammalia_
    _Aves_                            |
      |            _Reptilia_         |
      |                |              |
      +----------------+              |
                       |              |
                       +--------------+
                       |
                 _Proreptilia_
                       |          _Amphibia_
    _Pisces_           |              |
       |               |   +----------+
       |               |   |
       |               |   |        _Dipnoi_
       |         _Stegocephali_        |
       |               |               |
       |               +---------------+
       |               |
       +---------------+
                       |      _Cyclostomata_
                 _Proselachii_      |
                       |            |
    _Tunicata_         |   +--------+
        |              |   |
        |        *_Archicrania_*
        |              |           _Acrania_
        |              |               |
        |        *_Prospondylia_*------+
        |              |
        +----------+   |
                   |   |
                 *_Prochordonia_*


11. Stage of _Cyclostomata_. This now small group of Lampreys and
Hagfishes represents the lowest Craniota; and although much specialized
as a side-branch of the main-stem from which the other Craniota have
sprung, they give us an idea of what the direct ancestors of the latter
must have been like:--still without visceral arches, without jaws and
without paired limbs; with a persistent pronephros; the ear with one
semicircular canal only; mouth suctorial; cranium very primitive;
and the metamerism of the vertebral column indicated only by little
blocks of cartilage in the perichordal sheath. Such creatures must
have existed at least as early as the Lower Silurian epoch; but until
1890 fossil Cyclostomes were unknown. Their life in the mud, or as
endoparasites of fishes, coupled with their soft structure, makes them
very unfit for preservation. This gives all the greater importance to
Traquair's discovery, in 1890, of many little creatures, called by him
_Palæospondylus gunni_, in the Old Red Sandstone of Caithness, which
seem to be very closely allied to Cyclostomata.

12. The _Elasmobranchi_ (sharks and skates), with their immediate
forerunners, the Acanthodi of the Devonian and Carboniferous age,
are the first typical fishes. That they existed as far back as the
Silurian age is proved by many enamelled spines of the dermal armour,
chiefly from the dorsal fins. This higher stage is characterized by the
possession of typical jaws, by visceral or gill-bearing arches, and by
two pairs of limbs. None of the Elasmobranchs, fossil or recent, stands
in the direct ancestral line; but they are the lowest Gnathostomata,
jaw-and-limb-possessing creatures, known.

13. Closely connected with the Elasmobranchs in a wider sense are the
_Crossopterygii_, which begin in the Devonian age as a large group, but
have left only two survivals, the African Polypterus and Calamoichthys.
They are possessed of dermal bones and other ossifications, and are
characterized by their lobate paired fins, which have a thick axis
beset with biserial fin rays. Their gill-clefts are covered by an
operculum, and they have a well-developed air-bladder. Whilst they
are in many respects more highly developed than the Elasmobranchs,
and are intimately connected with the typical Ganoids and other
bony fishes (all of which form a great, manifold side-branch of the
general vertebrate stem), they stand in many other respects (notably,
the structure of the paired fins, the vertebral column, and the
air-bladder) nearer the main-stem of our own ancestral line.

14. This is shown by their intimate relation to the _Dipnoi_, which
are still represented by the Australian, African, and South American
mud-fishes: Ceratodus, Protopterus, and Lepidosiren. The genus
Ceratodus existed in the Upper Trias, whence various other unmistakably
dipnoous forms lead down through the Carboniferous (_e.g._, Ctenodus)
to the Devonian strata--_e.g._, Dipterus. They are characterized as
follows: The paired fins still retain the archipterygial form (namely,
one axis with biserial rays); the heart is already trilocular, and
receives blood which is mixed arterial and venous, owing to the gills
being retained, while the air-bladder has been modified into a lung. In
fact, the generalized Dipnoi form the actual link between fishes and
_Amphibia_.

15. _Amphibia._ The earliest amphibian fossils occur in
the Carboniferous strata. They alone--the Stegocephali or
Phractamphibia--stand in the ancestral line, while the Lissamphibia, to
which all the recent forms belong, are side-branches. The Stegocephali
are the earliest Tetrapoda, the archipterygial paired fins having been
transformed into the pentadactyle fore and hind limbs, which are so
characteristic of all the higher Vertebrata. The cranium is roofed
over by dermal bones, of which, besides others, supra-occipitals,
supra-orbitals, and supra-temporals are always present. The lowest
members (Branchiosauri) still retained gills besides the lungs, while
others (Microsauri) have lost the gills. Be it remembered that all
the recent Amphibia still undergo the same metamorphosis during their
ontogenetic development.

In the very important Temnospondyli, a subgroup of the
Stegocephali--_e.g._, Trimerorhachis of the Lower Red Sandstone or
Lower Permian--the component cartilaginous or bony units which compose
the vertebræ still remained in a separate, unfused state, showing at
the same time an arrangement whence has arisen that which is typical
of the Amniota. The same applies to the limbs and their girdles. In
fact, the Stegocephali, taken as a whole, lead imperceptibly to the
_Proreptilia_.

16. _Proreptilia_ are represented by the Permian genera Eryops and
Cricotus. Until quite recently these and many other fossils from
the Carboniferous strata were looked upon as Amphibia, while many
undoubted fossil Amphibia were mistaken for reptiles, as indicated by
the frequent termination '-saurus' in their names.

The nearest living representative of these extinct Proreptilia is
the New Zealand reptile Hatteria, or Sphenodon, close relations
of which are known from the Upper Trias; while others--_e.g._,
Palæohatteria--have been discovered in the Permian. Anyhow, Sphenodon
is the reptile which stands nearest to the main stem of our ancestry.

The most important characteristics of the Reptilia, which mark a higher
stage or level, are (1) The entire suppression of the gills--although
during the embryonic development the gill-clefts still appear in all
reptiles, birds, and mammals; (2) The development of an amnion and an
allantois, both for the embryonic life only, but so characteristic
that all these animals are comprised under the name of Amniota;
(3) The articulation of the skull with the first neck vertebræ by
well-developed condyles, either single (really triple) or double (such
a condylar arrangement begins with the Amphibia, but only the two
lateral condyles are developed, while the middle portion, belonging to
the basi-occipital element, remains rudimentary[21]); (4) The formation
of centra, or bodies of the vertebræ, mainly by a ventral pair of the
original quadruple constituents, or arcualia.

  [21] Similar conditions seem to have prevailed among the Proreptilia;
  but in those of their descendants which have specialized into Reptiles
  and Birds the basi-occipital element becomes more and more predominant
  in that formation which ultimately leads to the apparently single
  condyle. Hence it is misleading to divide the Tetrapoda into the two
  main groups of Amphi-and Mono-condylia, and therefrom to conclude that
  the two-condyled Mammalia are more closely related to the likewise
  amphicondylous Amphibia than to the so-called monocondylous Reptiles.

17. Between the Proreptilia and the Mammalia, which latter occur in
the Upper Triassic epoch, we have necessarily to intercalate a group
of very low reptiles, which are still so generalized that their
descendants could branch off either into the Reptilia proper or into
the Mammalia. The changes concerned chiefly the brain and the heart;
of the skeleton, the skull and the pelvis; and, of the tegumentary
structures, the formation of a hairy covering. Many such creatures
existed in the Triassic epoch--namely, the _Theromorpha_--some of which
indeed possess so many characteristics which otherwise occur in the
Mammalia only, that these creatures have been termed _Sauro-Mammalia_.
However, it has to be emphasized that none of the Theromorpha hitherto
discovered fulfils all the requirements which would entitle them to
this important linking position. They only give us an approximate idea
of what this link was like.

18. Stage of the _Promammalia_, or _Prototheria_. The only surviving
members are the famous duck-bill, Ornithorhynchus, and the spiny
ant-eaters, Echidna and Proechidna, of the Australian region. These
few genera, however, differ so much from one another in various
important respects that they cannot but be remnants of an originally
much larger group. Indeed, many fossils from the Upper Triassic and
from the Jurassic strata have without much doubt to be referred to the
Prototheria. The Prototheria are typical mammals, because they possess
the following characteristics: The heart is completely quadrilocular;
the blood is warm, and its red corpuscles have, owing to the loss
of their nucleus, been modified from biconvex into biconcave discs;
they have a hairy coat and sweat glands, and two occipital condyles;
the ilio-sacral connection is preacetabular; the ankle-joint is
cruro-tarsal; the quadrate bone of the Reptilia has ceased to carry the
under jaw, which now articulates directly with the squamosal portion
of the skull. Their low position is shown by the retention of the
following reptilian features: Complete coracoid bones and a T-shaped
interclavicle; a cloaca, or common chamber for the passage of the
fæces, the genital and the urinary products; they are still oviparous;
the embryo develops without a chorion, and is therefore not nourished
through a placenta. Even the milk glands, which are absolutely
peculiar to the Mammalia, are still in a very primitive stage, and do
not yet produce milk proper; and there is only a temporary shallow
marsupium.

19. Stage of _Metatheria_, or _Marsupialia_, are direct descendants of
Prototheria; but they show higher development by the reduction of the
coracoid bones and the interclavicle. The original cloaca is divided
into a rectal chamber and a uro-genital sinus, completely separated,
at least in the males; they are viviparous; the young are received
into a permanent marsupium, in the walls of which are formed typical
milk glands and nipples, but the embryo is still devoid of a placenta,
although some recent marsupials show indications of such an organ. The
corpus callosum in the brain is still very weak.

Most of the marsupials are extinct. They occur from the Upper Trias
onwards, and had in the Jurassic epoch attained a wide distribution
both in Europe and in America. Since the Tertiary epoch they have
been restricted to America and to the Australian region, and are now
represented by about 150 species.

20. Stage of _Prochoriata_, or early _Placentalia_: a further
development of the Metatheria by the development of a placenta, loss
of the marsupium and the marsupial bones, complete division by the
perineum of the anal and uro-genital chambers, stronger development of
the corpus callosum, or chief commissure of the two hemispheres of the
brain.

Placentalia must have come into existence during the Cretaceous
epoch. Up to that time all the Mammalia seem to have belonged to
either Prototheria or to Metatheria; but in the early Eocene we can
distinguish the main groups of Placentalia--namely, (1) Trogontia, now
represented by the rodents; (2) Edentata, or sloths, armadilloes, etc.;
(3) Carnassia, or Insectivora and Carnivora; (4) Chiroptera, or bats;
(5) Cetomorpha, or whales and dugongs; (6) Ungulata; (7) Primates.
Of these groups, the first and second, third and fourth, fifth and
sixth, can perhaps, to judge from palæontological evidence, be combined
into three greater groups, as indicated by the fossil Esthonychida,
Ictopsida, and Condylarthra, in addition to the ancestral Primates,
or Lemuravida, as the fourth large branch of the ancestral-tree where
this has reached the placental level. Among none of the first three
branches can we look for the ancestors of the Primates. The Lemuravida,
therefore, represent a branch equivalent to the three other branches.

21. Stage of _Lemures_, or _Prosimiæ_, comprising the older members of
the Primates, consequently approaching most nearly to the Lemuravida.
The limbs are modified into pentadactyle hands and feet of the arboreal
type, and are protected by nails. The dentition is of the frugivorous
or omnivorous type, with an originally complete series of teeth, with
milk teeth and with permanent. The orbit is surrounded by a complete
bony ring, posteriorly by a fronto-jugal arch, but still widely
communicating with the temporal fossa. The placenta is diffuse and
non-deciduous.

    ANCESTRAL TREE OF THE MAMMALIA.

  _'Systematische Phylogenie,' § 386._

            _Perissodactyla_      _Homo_                  _Carnivora_
                   | (_Litopterna_)  |                         | _Pinnipedia_
                   |       |         |                         |      |
                   +-------+   _Anthropoidae_                  +------+
  _Artiodactyla_   |                 |                         |
        |          |                 |                    _Carnassia_
        +----------+            _Catarhinæ_                    |
                   |                 |   _Chiroptera_          |
     _Proboscidea_ |                 |         | _Insectivora_ |
                |  |            _Platyrhinæ_   |       |       |
  (_Amblypoda_) |  |                 |         |       +-------+
        |       |  |                 |         |       |       _Rodentia_
        +-------+  |              _Simiæ_      +-------+           |
                |  |                 |                 |    (_Tillodontia_)
                +--+                 |                 |           |
  _Cetacea_        |                 |                 |      _Trogontia_
      | _Sirenia_  |             _Lemures_       _*Ictopsales*_    | _Edentata_
      |     |      |                 |                 |           |      |
    _Cetomorpha_   | _Hyracoidea_    |                 |      _*Esthonychales*_
         |         |      |          |                 |             |
         +---_?_---+------+          |                 |             |
                   |           _*Lemuravidæ*_          |             |
          _*Condylarthrales*_        |         +-------+             |
                   |                 |         |                     |
                   +--------Eutheria s. Placentalia------------------+
                                     |
                                     |    _Marsupialia polyprotodontia_
    _Marsupialia diprotodontia_      |                  |
                  |                  |                  |
                  +-------------Metatheria--------------+
                                     |
                                     |    _Monotremata_
                                     |          |           (_Allotheria_)
                                     |          |                 |
                                     |          +-----------------+
                                     |          |
                                Prototheria-----+
                                     |
                                     |
                    _*Hypotheria s.*_ _*Promammalia*_

  _Names in brackets indicate extinct groups.
  Names *underlined* indicate hypothetical groups or combinations._

22. Stage of _Simiæ_. Orbit completely separated from the temporal
fossa by an inward extension of the frontal and malar bones meeting the
alisphenoid. Placenta consolidated into a disc, and with a maternal
deciduous portion. Mammæ pectoral only. The dental formula is 2.1.3.3.
All the fingers and toes are protected by flat nails. The tail is long.
The American prehensile-tailed monkeys are a lower side-branch.

23. Stage of _Catarrhinæ Cercopithecidæ_. The dental formula is
2.1.2.3, owing to the loss of one pair of premolars in each jaw.
The frontal and alisphenoid bones are in contact, separating the
parietal from the malar bone; this feature is correlated with the
enlarged brain. The internarial septum is narrow, and the nostrils
look forwards and downwards instead of sidewards--hence the term
'Catarrhinæ.' The external auditory meatus is long and bony. The tail
is long, with the exception of _Macacus inuus_. The body is covered
with a thick coat of furry hair. Catarrhine monkeys have existed, we
know with certainty, since the Miocene.

24. Stage of _Catarrhinæ Anthropoidæ_, or _Apes_. Now represented by
the large apes--namely, the Hylobates or gibbon of South-Eastern Asia,
_Simia satyrus_, the orang-utan of Sumatra and Borneo, _Troglodytes
gorilla_, _T. niger_ and _T. calvus_, the gorilla and the chimpanzees
from Western Equatorial Africa. Of fossils are to be mentioned
Pliopithecus and Dryopithecus from European Miocene, and _Troglodytes
sivalensis_ from the Pliocene of the Punjaub. The tail is reduced
to a few caudal vertebræ, which are transformed into a coccyx, not
visible externally; but in the embryos of apes and man the tail is
still a conspicuous feature. The walk is semierect; in adaptation
to the prevailing arboreal life, the arms are longer than the legs.
The hair of the body is considerably more scanty than in the tailed
monkeys. _Troglodytes calvus_, a species or variety of chimpanzee, is
bald-headed. None of the recent genera of apes can lay claim to a place
in the ancestry of mankind.

25. Stage of _Pithecanthropi_. Hitherto the only known representative
is _Pithecanthropus erectus_, from the Upper Pliocene of Java. In
adaptation to a more erect gait, the legs have become stronger and the
hind-hand has been turned into a flat-soled walking 'foot.' The brain
is considerably enlarged. Presumably it is still devoid of so-called
articulate speech; this is indicated by the fact that children have
to learn the language of their parents, and by the circumstance that
comparative philology declares it impossible to reduce the chief human
languages to anything like one common origin.

26. _Man._ Known with certainty to have existed as an implement-using
creature in the last Glacial epoch. His probable origin cannot,
therefore, have been later than the beginning of the Plistocene. The
place of origin was probably somewhere in Southern Asia.

Whilst we have to admit that there are great defects in the older
(invertebrate) portion of our pedigree, we have all the more reason to
be satisfied with the positive results of our investigation of the more
recent (vertebrate) part of it. All modern researches have confirmed
the views of Lamarck, Darwin, and Huxley, and they allow of no doubt
that the nearest vertebrate ancestors of mankind were a series of
Tertiary Primates.

Particularly valuable are the admirable attempts of the two zoologists,
Paul and Fritz Sarasin,[22] to throw light upon the human phylogeny by
painstaking comparison of all the skeletal parts of man with those of
the anthropoid apes. They have shown that among the lower races of man
the primitive Veddahs of Ceylon approach the apes most nearly, and that
among the latter the chimpanzee stands nearest to man.

  [22] 'Ergebnisse naturwissenschaftlicher Forschungen auf Ceylon,' vols.
  4 and 5. (With an atlas of 84 plates; 1893.)

The direct descent of man from some extinct ape-like form is now beyond
doubt, and admits of being traced much more clearly than the origin
of many another mammalian order. The pedigrees of the Elephants, the
Sirenia, the Cetacea, and, above all, of the Edentata, for example,
are much more obscure and difficult to explain. In many parts of their
organization--for example, in the number and structure of his five
digits and toes--man and monkeys have remained much more primitive than
most of the Ungulata.

The immense significance of this positive knowledge of the origin of
man from some Primate does not require to be enforced. Its bearing
upon the highest questions of philosophy cannot be exaggerated. Among
modern philosophers no one has perceived this more deeply than Herbert
Spencer.[23] He is one of those older thinkers who before Darwin were
convinced that the theory of development is the only way to solve
the 'enigma of the world.' Spencer is also the champion of those
evolutionists who lay the greatest weight upon _progressive heredity_,
or the much combated _heredity of acquired characters_. From the first
he has severely attacked and criticised the theories of Weismann, who
denies this most important factor of phylogeny, and would explain
the whole of transformism by the 'all-sufficiency of selection.' In
England the theories of Weismann were received with enthusiastic
acclamation, much more so than on the Continent, and they were called
'Neo-Darwinism,' in opposition to the older conception of Evolution,
or 'Neo-Lamarckism.' Neither of those expressions is correct. Darwin
himself was convinced of the fundamental importance of progressive
heredity quite as much as his great predecessor Lamarck; as were also
Huxley and Spencer.

  [23] 'Principles of Biology': 'The Factors of Organic Evolution'; 'The
  Inadequacy of Natural Selection.'

Three times I had the good fortune to visit Darwin at Down, and on each
occasion we discussed this fundamental question in complete harmony.
I agree with Spencer in the conviction that progressive heredity is
an indispensable factor in every true monistic theory of Evolution,
and that it is one of its most important elements. If one denies with
Weismann the heredity of acquired characters, then it becomes necessary
to have recourse to purely mystical qualities of germ-plasm. I am of
the opinion of Spencer, that in that case it would be better to accept
a mysterious creation of all the various species as described in the
Mosaic account.

If we look at the results of modern anthropogeny from the highest point
of view, and compare all its empirical arguments, we are justified in
affirming that _the descent of man from an extinct Tertiary series of
Primates is not a vague hypothesis, but an historical fact_.

Of course, this fact cannot be proved _exactly_. We cannot explain all
the innumerable physical and chemical processes, all the physiological
mutations, which have led during untold millions of years from the
simplest Monera and from the unicellular Protista upwards to the
chimpanzee and to man. But the same consideration applies to all
historical facts. We all believe that Aristotle, Cæsar, and King Alfred
did live; but it is impossible to give a proof within the meaning of
modern exact science. We believe firmly in the former existence of
these and other great heroes of thought, because we know well the works
they have left behind them, and we see their effects in the history
of human culture. These indirect arguments do not furnish stronger
evidence than those of our history as vertebrates. We know of many
Jurassic mammals only a single bone, the under jaw. We all believe that
these mammals possessed also an upper jaw, a skull, and other bones.
But the so-called 'exact school,' which regards the transformation of
species as a hypothesis not proven, must suppose that the mandibula was
the only bone in the body of these curious animals.

Looking forward to the twentieth century, I am convinced that it will
universally accept our theory of descent, and that future science
will regard it as the greatest advance made in our time. I have no
doubt that the influence of the study of anthropogeny upon all other
branches of science will be fruitful and auspicious. The work done in
the present century by Lamarck and Darwin will in all future times be
considered one of the greatest conquests made by thinking man.

  EVOLUTIONARY STAGES OF THE PRINCIPAL GROUPS OF VERTEBRATA.[24]

  STAGES OF THE          CLASSES.             STAGES OF THE HEART.
  PAIRED LIMBS.

                       { 1. _Acrania._        I. _Leptocardia._
  I. _Adactylia_       {                        Cold-blooded; heart
    s. _Impinnata_.    {                        with one chamber;
    Without jaws       {                        without lungs.
    and limbs.         {
                       { 2. _Cyclostomata._ } II. _Ichthyocardia._
                                            }   Cold-blooded; heart
                                            }   two-chambered, with
                                            }   one atrium and one
                                            }   ventricle; heart
                                            }   containing venous
                                            }   blood only; without
  II. _Polydactylia_   { 3. _Pisces._       }   lungs.
    s. _Pinnata_.      {
    With two           {                    }  III. _Amphicardia._
    pairs of fins.     { 4. _Dipnoi._       }   Cold-blooded; heart
                                            }   with three complete
                                            }   chambers, namely, with
                                            }   two atria and one
                                            }   ventricle, or (Reptilia)
                       { 5. _Amphibia._     }   two ventricles with still
                       {                    }   incomplete septum; heart
                       {                    }   containing mixed venous
                       {                    }   and arterialized
  III. _Pentadactylia_ { 6. _Reptilia._     }   blood; with lungs.
    s. _Tetrapoda_.    {
    With two pairs     {                    { IV. _Thermocardia._
    of pentadactyle    {                    {   Warm-blooded; heart
    limbs (unless      { 7. _Aves._         {   with four complete
    they have          {                    {   chambers, namely, two
    been lost by       {                    {   auricles and two
    reduction).        {                    {   ventricles; right half
                       {                    {   of the heart with venous,
                       {                    {   left half with
                       {                    {   arterialized, blood; with
                       { 8. _Mammalia._     {   lungs.


  [24] Abridged from Haeckel's 'Systematische Phylogenie der
  Vertebraten,' § 14.




  BIOGRAPHICAL SKETCHES


JEAN BAPTISTE DE MONET, CHEVALIER DE LAMARCK, was born on
August 1, 1744, in Picardy, where his father owned land. Originally
educated for the Church, he soon enlisted, and distinguished himself
in active service. Owing to an accident affecting his health, the
young Lieutenant gave up the military career, and, without means,
studied medicine and natural sciences at Paris. In 1778 appeared his
'Flore française.' In 1793 he was appointed to a Chair of Zoology at
the newly-formed Musée d'Histoire Naturelle. He had the misfortune to
become gradually blind, and the last years of his life were spent amid
straitened circumstances. He died in 1829.

In 1794 Lamarck divided the whole animal kingdom into vertebrate and
invertebrate animals, and founded successively the groups of Crustacea,
Arachnida, Annelida, and Radiata. Between 1816 and 1822 he published
his celebrated 'Histoire naturelle des Animaux sans Vertèbres.'

His most famous work is the 'Philosophie zoologique,' 1809.

Assuming the spontaneous origin of life, he propounded the doctrine
that all animals and plants have arisen from low forms through
incessant modifications and changes. In this respect he was in absolute
opposition to Cuvier, who upheld the immutability of species, and did
his best by absolute silence to suppress the spread of the new doctrine.

Lamarck has explained his views of transformism chiefly in the seventh
chapter of the first volume of his 'Philosophie zoologique.'

Organisms strive to accommodate or adapt themselves to new
circumstances, or to satisfy new requirements--_e.g._, climate, mode
of procuring food, escape from enemies. The continued function of
parts of an organism changes the old and produces new organs. The
acquirements are inherited by the offspring, and thus are produced the
more complicated from simpler organisms. Continued disuse brings about
degeneration and ultimate loss of an organ.

Lamarck consequently sees in the adaptability, or power of adaptation,
which he assumes for all living matter the ultimate cause of variation;
and, as he was certainly the first to point out that acquired
characters are inherited by the progeny, he has given a working
explanation of Evolution.

But his doctrine did not spread--partly because he was misunderstood.
His theory, that a new want, by making itself felt, exacts from the
animal new exertions, perhaps from parts hitherto not used, until the
want is satisfied--this way of putting it sounds too teleological
to explain the yearned-for change in a mechanical or natural way.
Moreover, many of his examples lacked the exact basis of experiment
and observation necessary for their acceptance. Witness that of the
neck of the giraffe,--a never-failing source of ridicule to men who
cannot see the deeper purpose underlying the well-meant attempt at
an explanation, which failed from want of complete knowledge of the
intricate circumstances.

However, the theory of transformism was, so to speak, in the air;
and various authors have written on the subject, filling the gap
between Lamarck and Darwin, especially Goethe, Treviranus, Leopold
von Buch, and Herbert Spencer. But it is Darwin's immortal merit to
have opened our eyes by his theory of natural selection, which is, at
least, the first attempt to explain some of the causes and incidents
of organic Evolution in a natural mechanical way. Moreover, he was
the first clearly to express the fundamental principles of the theory
of descent, to elaborate what had been at best a general sketch of an
ill-defined problem, and to enter into detail, supported by a host
of painstaking observations, the making of which had taken him half a
lifetime. Darwin, without going further than cursorily into the causes
of variation, argued as follows: We know that variations do occur
in every kind of living creatures. Some of these variations lead to
something, while others do not. An enormously greater number of animals
and plants are born than reach maturity and can in their turn continue
the race. What is the regulating factor? His answer is, The struggle
for existence--in other words, the weeding out of the less fit, or
rather of the owners of those variations which are not so well adapted
to their surroundings.

For 'adapted' we had better read 'adaptable,' because a variation which
does not answer, which cannot be made use of, or, still more notably,
is a hindrance or disadvantage, does not become an adapted feature.
There is often a confusion between adaptation as an accomplished
fact, a feature, or resultant condition, and adaptation as the mode
of fitting the organism to, or making the best of, the prevailing
surroundings or circumstances.

ÉTIENNE GEOFFROY SAINT-HILAIRE was born in 1772 at Étampes,
Seine-et-Oise. He was originally brought up for the Church; but when
already ordained he attended lectures on natural science and medicine
in Paris. He managed to get the place of assistant in the Musée
d'Histoire Naturelle; he became Professor of Zoology in 1793, and took
the opportunity of encouraging young Cuvier. Later he became Professor
of Zoology of the Faculté des Sciences, and in 1818 he published his
remarkable 'Philosophie anatomique.' He died in 1844.

He had conceived the 'unity of organic composition,' meaning that there
is only one plan of construction,--the same principle, but varied in
its accessory parts. In 1830, when Geoffroy proceeded to apply to the
Invertebrata his views as to the uniformity of animal composition,
he found a vigorous opponent in Cuvier. Geoffroy, like Goethe, held
that there is in Nature a law of compensation, or balancing of growth,
so that if one organ take on an excess of development, it is at the
expense of another part; and he maintained that, since Nature takes no
sudden leaps, even organs which are superfluous in any given species,
if they have played an important part in other species of the same
family, are retained as rudiments, which testify to the permanence
of the general plan of creation. It was his conviction that, owing
to the conditions of life, the same forms had _not_ been perpetuated
since the origin of all things, although it was not his belief that
existing species were becoming modified. Cuvier, on the other hand,
maintained the absolute invariability of species, which, he declared,
had been created with regard to the circumstances in which they were
placed, each organ contrived with a view to the function it had
to fulfil,--thus putting the effect for the cause ('Encyclopædia
Britannica,' 9th edition, vol. xxi., p. 171).

GEORGE CUVIER was born in 1769 at Montbéliard, in the department of
Doubs, which at that time belonged to Württemberg. He was educated at
Stuttgart, and studied political economy. While acting as private tutor
to a French family in France he followed his favourite pursuit, the
study of natural sciences. Geoffroy Saint-Hilaire heard of him, and
appointed him assistant in the department of comparative anatomy in the
Musée d'Histoire Naturelle. In 1799 he was elected Professor of Natural
History at the Collège de France, and soon after he became Perpetual
Secretary of the Institut National. In 1831, a year before his death,
Louis Philippe raised him to the rank of a peer of France.

Cuvier was the first to indicate the true principle upon which the
natural classification of animals should be based--namely, their
structure. It is the study of the anatomy of the creatures and their
comparison which affords the only sound basis of a classification.
The work which had the greatest influence upon the scientific public
is his 'Règne animal distribué d'après son Organisation,' 1817. The
system which he propounded in this book gradually came to have almost
world-wide fame, and, in spite of its many obvious deficiencies, still
lingers in some of our most recent text-books.

A standard work is his 'Leçons d'Anatomie comparée,' and, in truth, he
is the founder of that kind of comparative anatomy which was brought
to such a high state by his pupil, the late Sir Richard Owen. Cuvier
discovered the law of 'correlation of growth,' and was the first to
apply this law to the reconstruction of animals from fragments: see his
monumental work entitled 'Recherches sur les Ossemens fossiles,' 1812.

Cuvier, however, as a strict matter-of-fact man, was incapable of
appreciating the speculative conclusions which were drawn by his
contemporaries Saint-Hilaire and Lamarck. On the contrary, he firmly
stuck to the doctrine of the immutability of species; and, in order to
account for the existence of animals whose kind exists no longer, he
invented the famous doctrine of successive cataclysms.

KARL ERNST VON BAER was born in 1792 in Esthonia, studied at Dorpat
and then at Würzburg, where Döllinger introduced him to comparative
anatomy. For a few years he was a _Privat-docent_ at Berlin; then he
went to Königsberg as Professor of Zoology and Embryology. In 1834
he became an Academician at St. Petersburg, where for many years he
was occupied with the most varied studies, chiefly geographical and
ethnological. The last years of his long, active life he spent in
contemplative retirement on his paternal estate, and he died at Dorpat
in 1876.

While still at Würzburg he induced his friend Pander, a young man
of means, to study the development of the chick; and Pander was the
first to start the theory of the germinal layers from which all the
organs arise. Baer, however, continued these researches in Königsberg,
and after nine years' labour produced his epoch-making work, 'Ueber
Entwicklungsgeschichte der Thiere: Beobachtung und Reflexion,'
Königsberg, 1828. Nine years later he completed the second volume.
He established upon a firm basis the theory of the germinal layers,
and by further 'reflexions' arrived at the elucidation of some of the
most fundamental laws of biology. For example, in the first volume
he made the following prophetic statement: 'Perhaps all animals are
alike, and nothing but hollow globes at their earliest developmental
beginning. The farther back we trace their development, the more
resemblance we find in the most different creatures. And this leads to
the question whether at the beginning of their development all animals
are essentially alike, and referable to one common ancestral form.
Considering that the "germ" (which at a certain stage appears in the
shape of a hollow globe or bag) is the undeveloped animal itself, we
are not without reason for assuming that the common fundamental form is
that of a simple vesicle, from which every animal is evolved, not only
theoretically, but historically.'

This statement is all the more wonderful when we consider that the
cells, the all-composing individual units, were not discovered until
ten years later.

In 1829 Baer discovered the human egg, and later the chorda dorsalis.
In an address delivered in 1834, entitled 'The Most Universal Law
of Nature in all Development,' he explained that only from a most
superficial point of view can the various species be looked upon as
permanent and immutable types; that, on the contrary, they can be
nothing but passing stages, or series of stages, of development, which
have been evolved by transformation out of common ancestral forms.

JOHANNES MUELLER, born at Coblenz in 1801, established himself
as _Privat-docent_ at Bonn, where in 1830 he became Professor of
Physiology. In 1833 he accepted the Chair of Anatomy and Physiology at
Berlin, where he died in 1858.

He was one of the most distinguished physiologists and comparative
anatomists. By summarizing the labours and discoveries already made in
the field of physiology, by reducing them to order, and abstracting the
general principles, he became the founder of modern physiology. But
he was scarcely less distinguished by his researches in comparative
anatomy. His 'Vergleichende Anatomie der Myxinoiden,' in _Abhandlungen
der Berliner Akademie_, 1835-45, and 'Ueber die Grenzen der Ganoiden'
(_ibid._, 1846), are standard works of lasting value.

Mueller exercised a stimulative influence as a teacher. Many well-known
men--such as Helmholtz, Gegenbaur, Bruecke the physiologist, Guenther
the zoologist, Virchow the pathologist, Koelliker and Haeckel--have
been his pupils.

RUDOLPH VIRCHOW was born in 1821 at Schievelbein, a small
town in Eastern Pomerania. He studied medicine in Berlin as a pupil
of Johannes Mueller, and went in 1849 to Würzburg, where, under the
influence of Koelliker, and Leydig the pathologist, he laid the
foundation of an entirely new branch of medical science--that of
'cellular pathology.' Since 1856 he has filled the principal Chair of
Pathology at Berlin. In 1892 he received the Copley medal of the Royal
Society.

'His contributions to the study of morbid anatomy have thrown light
upon the diseases of every part of the body; but the broad and
philosophical view he has taken of the processes of pathology has
done more than his most brilliant observations to make the science of
disease.

'In pathology, strictly so called, his two great achievements--the
detection of the cellular activity which lies at the bottom of
all morbid as well as normal physiological processes, and the
classification of the important group of new growths on a natural
histological basis--have each of them not only made an epoch in
medicine, but have also been the occasion of fresh extension of science
by other labourers' (Proc. Royal Soc., 1892).

Virchow has not confined himself to medicine. He takes the keenest
interest in anthropology and ethnology, on which subjects he has
contributed many papers. Together with his colleagues Helmholtz the
physicist, and Du Bois Reymond the physiologist, he has taken a leading
place in the spreading of natural science; but, unfortunately, he
did not take to the doctrine of Evolution, and for the last thirty
years has been its declared antagonist, rarely missing an opportunity
of denouncing everything but descriptive anatomy and zoology as the
unsound speculations of dreamers. This has on more than one occasion
brought him into sharp conflict with Haeckel. His activity is
astonishing, especially if it be remembered that Virchow has for many
years been one of the most conspicuous leaders of the Progressists and
Radicals in the German Parliament and Berlin town-council.

EDWARD DRINKER COPE was born at Philadelphia, Pa. After studying at
several Continental Universities, especially at Heidelberg, he became
first Professor of Natural Science at Haverford College, and later
Professor of Geology and Mineralogy. He died at an early age in 1897.
As a member of various geological expeditions and other surveys, he
explored chiefly Kansas, Wyoming, and Colorado; and he published many
most suggestive papers on the fossil vertebrate fauna of North America,
and on classification especially of Amphibia and Reptiles.

Among works of a more general philosophical scope may be mentioned 'The
Origin of the Fittest,' 1887, and his latest work, 'The Primary Factors
of Organic Evolution,' 1896.

ALBERT VON KOELLIKER, born in 1817, became Professor of Anatomy at
Würzburg. His earlier studies and discoveries contributed considerably
to the systematic development of the cell theory. In 1844 he observed
the division and further multiplication of the original egg cell. Next
year he showed the continuity between nerve cells and nerve fibres in
the Vertebrata; later, that the non-striped or smooth muscular tissue
is composed of cellular elements. He demonstrated that the Gregarinæ
are unicellular creatures. In 1852 he went with his younger friend
Gegenbaur to Messina, where he studied especially the development
of the Cephalopoda (cuttlefishes and allies); and he produced a
magnificent work on Alcyonaria, Medusæ, and other allied forms. He
elucidated the development of the vertebral column, especially with
reference to the notochord.

In 1848 he founded, together with Th. von Siebold, the famous
_Zeitschrift für wissenschaftliche Zoologie_.

A standard work on mammalian embryology is his 'Entwicklungsgeschichte
des Menschen und der höheren Thiere,' a text-book of which the second
edition appeared in 1879.

At the anniversary meeting of 1897 he received the Copley medal, the
highest honour which the Royal Society can bestow.

CARL GEGENBAUR was born on August 21, 1826, in Bavaria. He studied
medicine and kindred subjects in Würzburg, and as a pupil of Johannes
Mueller in Berlin.

In 1852 he went with Koelliker to Messina to study the structure and
development of the marine fauna. Important papers on Siphonophora,
Echinoderms, Pteropoda, and, later, Hydrozoa and Mollusca, were the
result. Soon after his return he was offered the chair of Anatomy at
Jena, and at this retired spot he produced his most important works,
devoting himself more and more to the study of the Vertebrata. Since
1875 he has held the Chair of Anatomy at Heidelberg.

In 1859 he published his 'Principles of Comparative Anatomy'; but in
1870 he remodelled it completely, the theory of descent being the
guiding principle. These 'Grundzüge' were followed by a somewhat more
condensed 'Grundriss,' the second edition of which was published
in 1878, and has been translated into French and English. In the
meantime he had broken new ground by the development and treatment of
certain problems concerning the composition and origin of the limbs,
the shoulder-girdle and the skull, researches which are embodied in
his 'Untersuchungen zur vergleichenden Anatomie der Wirbelthiere,'
1864-65-72.

In 1883 he brought out a text-book on human anatomy. This also marked
a new epoch, because for the first time, not only the nomenclature,
but also the general treatment of human anatomy, was put upon a firm
comparative anatomical basis. The success of this work is indicated by
the fact that it reached the sixth edition in 1897.

Lastly, in 1898, appeared the first volume of what may be called his
crowning work, 'Vergleichende Anatomie der Wirbelthiere.'

Gegenbaur is universally recognised, not only as the greatest living
comparative anatomist, but also as the founder of the modern side of
this science, by having based it on the theory of descent.

In 1896 he received from the Royal Society the Copley medal 'for
his pre-eminence in the science of comparative anatomy or animal
morphology.'

His marvellously powerful influence as a teacher and investigator has
made Heidelberg a centre whence many pupils have spread his teaching,
and above all his method of research.

ERNST HEINRICH HAECKEL was born on February 16, 1834, at Potsdam. He
carried out his academical studies alternately at Berlin and Würzburg,
attracted by such men as Johannes Mueller, Koelliker, and Virchow.
For years he was undecided what his career should be, whether that
of botanist, collector, or geographical traveller. Certainly that of
medicine attracted him least, although in deference to his father's
wishes he qualified and settled down for a year's practice in Berlin.
As he himself has told us, he might perhaps have proved rather
successful as a physician, to judge from the fact that he did not lose
a single patient. But 'I had only three patients all told, and the
reason of this is perhaps that I had given on my plate the hours of
consultation as from 5 to 6 _a.m._'

During the year 1859 he travelled as medical man and artist in Sicily.
In 1861 he was induced by Gegenbaur, whose acquaintance he had made in
Würzburg, to establish himself as a _Privat-docent_ for comparative
anatomy in Jena. And there he has remained ever since, filling the
Chair of Zoology, and having declined several much more tempting offers
from the Universities of Würzburg, Vienna, Strassburg, and Bonn.

Within one year, 1865, he wrote the two volumes of his 'Generelle
Morphologie der Organismen,' as he himself relates, in order to master
his sorrow over the loss of his first wife. But he broke down, and went
to the Canaries to recruit health and strength. The 'Morphologie,'
which has long been out of print,[25] made scarcely any impression. It
was ignored, probably because he had placed the old-fashioned study of
zoology and morphology upon a thoroughly Darwinistic basis.

[25] That this great work is now comparatively rare, although still
in the second-hand market, may perhaps be urged in excuse of the
fact of so many attempts made by many authors, both professional and
amateur, to find fault with or to explain the principles of adaptation,
variation, heredity, cænogenesis, phylogeny, etc., in complete
ignorance that all these and many more fundamental questions were fully
discussed more than thirty years ago in the 'Generelle Morphologie.'

On the advice of his friend Gegenbaur, he gave a more popularly
written abstract of his 'Generelle Morphologie'--in fact, the
substance of a series of his lectures--in the shape of his 'Natürliche
Schöpfungsgeschichte.' This 'History of Natural Creation,' which
in 1898 has reached the ninth edition (first edition translated
into English in 1873), had the desired effect. So also had his
'Anthropogenie oder Entwicklungsgeschichte des Menschen,' the fourth
edition of which appeared in 1891.

It was a lucky coincidence that Haeckel had just finished his
preliminary academical studies, was entirely at leisure, and
undetermined to which branch of natural science he should devote his
genius, when Darwin's great work was given to the world. Haeckel
embraced the new doctrine fervently, and, as Huxley was doing in
England, he spread it and fought for it with ever-increasing vigour in
Germany.

With marvellous vigour and quickness of perception he applied the
principles of Evolution or the theory of descent to the whole organic
world, and not only opened entirely new vistas for the study of
morphology, but also worked them out and fixed them. He was the first
to draw up pedigrees of the various larger groups of animals and
plants, filling the gaps by fossils or with hypothetical forms (the
necessary existence of which he arrived at by logical deductions);
and thus he reconstructed the first universal pedigree, a gigantic
ancestral tree, from the simple unicellular Amoeba to Man. Of course
these pedigrees were entirely provisional, as he himself has over and
over again avowed; but they are, nevertheless, the ideal which all
systematists and morphologists working upon the basis of Evolution have
since been seeking to establish.

Naturally he was vigorously attacked, not only by anti-Darwinians,
or rather anti-Evolutionists, but also by many of those who, having
accepted the principle of transformism, ought to have known better.
Perhaps they thought they did know better. Imperfections or mistakes in
details of the grand attempt,--and these, naturally, were many,--were
singled out as samples of the whole, which was ridiculed as the romance
of a dreamer.

In the end, however, this hostility, narrow-minded and unfair in
many respects, has done good to the cause. There has arisen an
ever-increasing school of workers in favour of the new doctrine. Owing
to renewed research, criticism, corrections in all directions, we
now know considerably more about natural classification (and this is
pedigree) than when Haeckel first opened out the whole problem.

Owing to his fearless mode of exposition, regardless of the indignant
wrath which the new doctrine aroused in certain ecclesiastical
quarters, Haeckel bore the brunt of almost endless attacks, and had to
write polemical essays. The result has been that friend and foe alike
are now working on the lines which he has laid down; most of the ideas
which he was the first to conceive, and to formulate by inventing a
scientific terminology for them, have become important branches, or
even disciplines, of the science.

Most morphologists of the younger generations now take these terms
for granted, without remembering the name of their founder. It is,
therefore, perhaps not quite superfluous to mention some of them:

_Phylum_, or stem, the sum total of all those organisms which have
probably descended from one common lower form. He distinguished eight
such phyla--Protozoa, Coelenterata, Helminthes or Vermes, Tunicata,
Mollusca, Articulata, and Vertebrata. The phyla are more or less
analogous to 'super-classes,' large branches or 'circles,' or principal
groups of other zoologists.

_Phylogeny_, the history of the development of these various phyla,
classes, orders, families, and species.

_Ontogeny_, the history or study of the development of the individual,
generally called embryology. In reality the scope of embryology
is the ontogenetic study of the various species, and this branch
of developmental study alone can be checked by direct, 'exact'
observation, for the simple reason that the individuals alone are
entities, while the species, genera, families, etc., are abstract ideas.

The _ontogenesis of any given living organism is a short, condensed
recapitulation of its ancestral history or of its phylogenesis_. This
is Haeckel's 'fundamental biogenetic law.'

A complete proof of the phylogeny of any creature would be given by
the preservation of an unbroken series of all its fossil ancestors.
Such a series will in most cases, for obvious reasons, always remain a
desideratum. In a few cases, however, the desideratum is nearly met:
for example, the ancestral line of the one-toed digitigrade horse from
a four-or five-toed plantigrade and still very generalized Ungulate is
approaching completion.

Phylogenetic study has to rely upon other help. This is afforded by
comparative anatomy and by the study of ontogeny. If the latter were
a faithful, unbroken recapitulation of all the stages through which
the ancestors have passed, the whole matter would be very simple; but
we know for certain that in the individual development many stages
are left out (or, rather, are hurried through, and are so condensed
by short-cuts being taken that we cannot observe them), while other
features which have been introduced obscure, and occasionally modify
beyond recognition, the original course.

Again, the sequence of the appearance of the various organs is
frequently upset (_heterochronism_). Some organs are accelerated in
their development, while others, which we know to be phylogenetically
older, are retarded in making their reappearance in the embryo.

These disturbing or distorting newly introduced features or factors
show themselves chiefly in connection with the embryonic conditions of
growth--for example, yolk-sac, placenta, amnion. They all come within
the category of _cænogenesis_: they are cænogenetic, while the true,
undisturbed recapitulation is _palingenetic_.

Lastly, some features, so-called rudimentary or vestigial organs,
instead of disappearing, are most tenacious in their recurrence,
while others of originally fundamental importance scarcely leave
recognisable traces, and are, so to speak, only hinted at during the
embryonic growth of the creature we happen to study. Hence arises the
philosophical study of 'Dysteleology.'

Among other terms invented by Haeckel, and now in general use, are
_Metamere_, _Metamerism_, _Coelom_, _Gonochorism_, _Gastrula_,
_Metazoa_, _Gnathostomata_, _Acrania_, _Craniota_, and _Amniota_.

Hitherto we have dealt with his general work only, a résumé of which
he gave for many years in a course of thirty lectures before an
audience composed of 'all sorts and conditions of men.' Students of
biology and of medicine side by side with theologians, incipient and
ordained, jurists, political economists, and philosophers, crowded his
lecture-room during the 'seventies to hear the master explaining the
'natural history of creation' or the mysteries of anthropogenesis.
Another course of eighty lectures during the winter semester was, and
still is, devoted to a systematic treatment of zoology, while practical
classes are reserved for the more select.

His winning personality and fascinating eloquence, combined with a
clear and concise delivery, have gained the enthusiastic admiration of
many a student who went to the quiet University town in order to learn
with his own ears and eyes.

_List of Separate Publications by Professor Haeckel._

'Biologische Studien. I.: Studien ueber die Moneren und andere
Protisten.' Leipzig, 1870 (out of print). He was the first to
make observations on the natural history of the Monera, living
bits of protoplasm, devoid even of a nucleus--_e.g._, _Protogenes
primordialis_, _Protomyxa aurantiaca_.

'Monographie der Radiolarien.' Berlin, 1862-88. With 171 plates.

'Entwicklungsgeschichte der Siphonophoren.' Utrecht, 1869.

'Plankton-Studien. Vergleichende Untersuchungen ueber die Bedeutung und
Zusammensetzung der pelagischen Fauna und Flora.' Jena, 1880.

'Metagenesis und Hypogenesis von Aurelia aurita.' Jena, 1881.

'Monographie der Geryoniden oder Ruesselquallen.' Leipzig, 1865.

'Generelle Morphologie der Organismen.' 2 vols. Berlin, 1866.

'Anthropogenie oder Entwicklungsgeschichte des Menschen,' 1874; 4th
edition, 1891.

'Natuerliche Schoepfungs-Geschichte.' 2 vols. Berlin, 1st edition,
1868; 9th edition, 1898. This work has been translated into most
European languages (the first edition in English, under the title
'Natural History of Creation' in 1873; the eighth in 1892).

'Monographie der Kalkschwaemme.' 3 vols. Berlin, 1872 (out of print).
With the subtitle, 'An Attempt to solve analytically the Problem of
the Origin of Species.' In this work, illustrated by sixty plates, he
showed that the Calcispongia are individually so yielding, so adaptive
to external influences, that it is practically impossible to break up
the whole group into anything like satisfactory species or genera.
According to predilection, we can distinguish either 1 genus with only
3 species, or 3, 21, 43 genera, with 21, 111, 181, or 289 species
respectively.

In this work, in 1872, Haeckel established the homology of the two
primary layers, ecto- and endoderm, throughout the Metazoa. The attempt
to do the same for the four secondary layers, as made in the second
part of his 'Gastræa-theory,' failed. It caused an enormous amount of
research, hitherto without a satisfactory solution of the problem.

'Studien zur Gastræa-Theorie.' Jena, 1874. The transformation of
the single primitive egg-cell by cleavage into a globular mass of
cells (Morula)--which latter, becoming hollow (and then known as the
Blastula), turns ultimately by invagination or by delamination into
the Gastrula--is a series of processes which applies to all Metazoa.
The Gastrula is, therefore, the ancestral form of the Metazoa; and the
Gastræa-theory, founded by Haeckel, throws light, on the one hand, upon
the mystery of the phyletic connection of the various animal groups,
while, on the other hand, it connects the Metazoa, or multicellular
organisms, with the lowest Protozoa. We come to this conclusion
becaues the Gastrula arises from and passes through stages which exist as
independent, permanent organisms among the Protozoa.

Needless to say this Gastræa-theory has been violently attacked in
detail, with the result that various modifications of the Gastrula,
until then undreamed of, have become known.

'Monographie der Medusen.' Jena, 1879-81. With 72 coloured plates.

'Reports on the Scientific Results of the Voyage of H.M.S.
_Challenger_.' With 230 plates:

  1. Deep-sea Medusæ. 1881.
  2. Radiolaria. 1887.
  3. Siphonophoræ. 1888.
  4. Deep-sea Keratosa. 1889.

A short holiday spent on the coasts of the Red Sea produced the volume
'Arabische Korallen' (Berlin, 1876); and a longer trip to Ceylon has
been described in 'Indische Reisebriefe,' of which the third edition
appeared in 1893. The English translation (1883) is entitled 'A Visit
to Ceylon.'

'Monism as connecting Religion and Science: the Confession of Faith of
a Man of Science.' 1894.

Haeckels latest work is the 'Systematische Phylogenie' (Berlin, 1896),
three volumes dealing with Protistæ and Plants, Invertebrata and
Vertebrata. They contain the author's views on the natural system of
the organic world, both living and extinct. Notable in the work are
the many reconstructions of ancestral forms which, provided Evolution
is true, must have existed--hypothetical until they, or something like
them, are found in a fossil state. Everybody who works systematically,
and upon the basis of Evolution, does, sometimes unconsciously,
reconstruct such links, although he may perhaps not see the necessity,
or have the courage to fix his vision, by assigning to it all those
attributes or characters which are indicated by deductions from
comparative anatomy, palæontology, and embryology.




  THEORY OF CELLS.


The vegetable cell was discovered by _Schleiden_, Professor of Botany
at Jena, in 1838. Next year _Schwann_ found the animal cell.

In 1844 _Koelliker_ discovered that the egg cell, by division and
multiplication, becomes an aggregation--a heap of new cells.

In 1849 _Huxley_ found the two primary layers (observed long before
by _Pander_ and _Baer_ in the chick) also in certain Invertebrata,
the Medusæ; and he called these layers 'ectoderm' and 'endoderm'
respectively.

In 1851 _Remak_, in his 'Untersuchungen über die Entwicklung der
Thiere,' showed the egg to be a simple cell, and that from it, by
repeated division or multiplication, arise the germinal layers, and
that by differentiation of the cells of these layers are formed all the
tissues of the body.

_Kowalevsky_, of St. Petersburg, found the two primary germinal layers
also in Worms, Echinoderms, Articulata, and other animals.

_Haeckel_, in 1872, found the same in the Sponges. He stated that these
two germinal layers occur in all animals, except in the Protozoa;
and that they are homologous, or equivalent, in all the groups of
animals, from the Sponges up to Man. In 1873, in his 'Gastræa-theorie,'
he explained the phylogenetic significance, and tried to show the
homology, of the four secondary germinal layers.




  FACTORS OF EVOLUTION.


An organism, as living matter, does not stand in opposition to,
or outside of, the rest of the world. It is part of the world. It
receives matter from its surroundings, and gives some back; therefore
it is influenced by its surroundings. It is acted upon, and it reacts
upon the latter, and if these change (and they are nowhere and never
strictly the same) the organism also _varies_. It _adapts_ itself, and
if it does not, or, rather, cannot, do so, it dies, because it is unfit
to live in the world, or, rather, in those particular surroundings
and conditions in which it happens to be. That organism which yields
most easily, accommodates itself most quickly, has the best chance of
existence--_survival of the fittest_. 'Fitness' in this case does not
mean fitness to live, but rather a particular condition which happens
to fit into the new circumstances.

Adaptation and variation are simultaneous: they are fundamentally the
same. If there were no adaptability and no variability, those simplest
of organisms which we suppose to have sprung into existence in the
pre-Cambrian period would long ago have ceased to exist.

It is the physiological momentum which models the organism, and, by
causing its adaptations, has produced its organs by change of function.
Gegenbaur illustrates this most important fundamental truth by an
excellent example. Suppose that, in an absolutely simple organism, all
the parts of its exterior are under the same functional conditions,
so that each part of the surface can take in food, and that this is
digested, assimilated, in the interior. There is, in this condition,
not yet any definite organ. If this organism sinks to the bottom and
becomes sessile, this part is excluded from taking in nourishing
matter, while the opposite surface alone remains, or becomes more, fit
for this function. Thus, a simple variation and adaptation has been
produced, and if the same organism continues in this position, its
bottom cells will estrange themselves from their original function,
while those on the top will convey the food into the interior, where
a cavity will be formed, ultimately with a permanent opening, the
primitive gut and mouth, both very different from the 'foot.'

Thus, by adaptation and variation the organism acquires new functions,
organs, features, and it gives up and eventually loses others. Its
offspring is like it. Like produces like. This is the principle of
_heredity_. Adaptation, when going on generation after generation on
the same lines in the same direction, becomes continuous, and has an
intensifying, _cumulative_ effect. By always weeding out from a flock
of pigeons those birds which possess more dark feathers than the rest,
we ultimately produce an entirely white race. We hurry on what Nature
does slowly.

The inheritance of acquired characters becomes very obvious in the
following example: The Monera are the lowest living organisms known;
they consist of a mass of protoplasm, and are still devoid of even
a nucleus. They multiply simply by division; each half is like the
other, and like the parent (which by this process has ceased to exist),
except that each is smaller and has to grow. A certain Moneron,
_Protomyxa aurantiaca_, is orange-coloured, and its offspring is from
the beginning of the same colour, and this colour has been acquired
by that kind of Monera-like protoplasm which thereby has become the
species called Aurantiaca. We have no reason for assuming that there
existed from the beginning of life not only colourless, but also red,
orange, and other kinds of protoplasm. In these simplest of organisms
the whole process of heredity seems very obvious; but in the higher
ones, in those which propagate by eggs, the problem is infinitely
more complicated. It is true that the egg is, strictly, nothing but
a small part of the parental organism, and we know from everyday
experience that this single egg-cell has in it all the attributes and
characteristics of the parent; but these attributes and characteristics
make their appearance successively, just as the egg cell of a chick has
neither wings nor feathers, not even a backbone, but develops these
organs because its parents have them.

The theory that acquired characters are hereditary has often been
vigorously attacked; but the champions of the negative position have
not given us anything satisfactory instead. They question, also, the
principle of adaptation as a factor in Evolution, and substitute
'variation,' coupled with 'natural selection.'

They point to Darwin's argument: (1) It is a fact that animals and
plants produce a much greater number of young than in their turn grow
up to propagate the race; (2) no two of the frequently many individuals
of the same breed are exactly alike, although the differences may be
hidden to our perception (this is quite true, because no two entities
can live in absolutely the same place and conditions); (3) through
heredity the offspring takes over the faculties and features of the
parents; (4) what decides which of the many individuals (each one
possessing some aberration or variation) are to live and to propagate
the race?--obviously those individual variations which happen to make
the lucky possessors most fit for the struggle for life.

So far, well; but the 'Neo-Darwinians' imagine that 'adaptation'
is not the cause, but the result, the effect, of the formation of
species. According to them, the species are neither adapted by, nor do
they adapt themselves to, their surroundings. Adaptation is to them
an accomplished fact, a condition which a species happens to be in
because its particular variation is the one which, to the exclusion of
others, suits or fits into its surroundings. Such a view simply takes
variation for granted, and stipulates it as a something _a priori_,
without raising the further necessary question, why there should be
any variations at all. Why, indeed, unless they are caused by external
influences? Haeckel elucidated this by the conception of adaptation as
explained in the foregoing pages.

These and kindred speculations have produced some rather curious
discussions, which not infrequently end in conundrums. If we speak of
a case of adaptation as a condition, a fact, we easily run the risk
of getting into confusion about cause and effect. For example: Is the
stag swift because he has long and slender legs, or are his legs long
because he is swift? In reality, swiftness and length of legs are cause
and effect in one. His legs have been so modified as to make him swift,
because he has put them continuously to whatever was his full speed,
which in his thick-footed ancestors was probably a very slow one. The
above question reads, therefore, more sensibly as follows: Has the stag
become swift because his legs have become long and slender, or have his
legs become long and slender because he has attained swiftness? Now, we
see that both halves of the double question are practically the same
and instantly suggest the answer.

A fundamental difference between artificial machines and living
organisms is that the former are worn out by use, while the latter not
only repair the loss caused by use, but are also stimulated to further
increase. On the other hand, organs which are not put into function,
or are not used, _degenerate_. The various cells of the organ react
upon external stimuli by increased activity. Why this should be so is
another question--perhaps because those which do not would soon be not
fit to survive. Each cell has a function; the more specialized the more
intense it is. Every external stimulus, every contact with the outer
surroundings, is an insult, necessarily of detrimental effect, as it
disturbs the equilibrium of the cell body. It must, therefore, be of
advantage to the cells' well-being to return as soon as possible to the
_status quo ante_, and this can only be done by increased activity.

In the present state of our knowledge, we can approach only the
simplest cases of acquisition of characteristics. Mostly they are
so complicated, subject to so many unthought-of conditions, that we
do not know from which end to approach the problem. Frequently the
supposed use of certain obvious features is the merest guesswork. This
applies especially to features to which we are not accustomed (although
wrongly so) to assign a function--for example, coloration. A green
tree-frog will with predilection rest on green leaves. The advantages
of concealment are obvious, and in this case he 'adapts himself' to the
surroundings by making for green localities: if he did not he would
be eaten up sooner than his more circumspect comrades. But this making
for, and sitting in, the green has not _necessarily_ made him of that
colour. Extreme advocates of one view would argue as follows: Once upon
a time there were among the offspring of ancestral tree-frogs some
which, among other colours, exhibited green, not much, perhaps not even
perceptible to our eyes. The occurrence of this colour, according to
them, was spontaneous, a freak--as if in reality there were anything
spontaneous in the sense of being causeless. The descendants of these
more greenish creatures, provided they did not pair with frogs of the
ordinary set, became still greener (by accumulative inheritance), and
so on, until the green was pronounced sufficient to be of advantage
when competition could set in.

With this view there is always the difficulty of understanding how the
initial very small changes can be useful, unless we have to deal with
extremely simple organisms. Is it likely in the case of our frogs that
an almost imperceptible variation in colour makes them more fit to
live? We have to assume that 'luck' or chance kept them for generations
out of harm's reach, until the accumulation of green, hitherto quite
ineffective, neither harmful nor useful, became strong enough to be
effective. Such cases undoubtedly happen.

But we can also argue out this problem in a somewhat different way,
which goes nearer to the root of the whole process. The original
slight, imperceptible change in pigmentation is not a spontaneous
freak; it was caused by the direct influence of the surroundings in
which the particular frogs happened to live, be this factor light or
temperature or food. Thus it stands to reason that the offspring,
living under similar conditions, will be acted upon in the same way.
That factor which has added green to the parents will add green to the
children, until by accumulative inheritance a more decidedly green
race is produced.

The offspring of green plants do not become green when grown in the
dark; the young plants inherit not the green, but the capacity of
becoming green when acted upon by sunlight. This as an instance of
direct influence of the surroundings on a substance (chlorophyll),
which has not yet performed a function. But the kittens of a pair of
black cats produce black hair before they are born, and we have no
reason to doubt that the black pigment in their tegumentary structures
is ultimately referable to the action of the sunlight. In many
instances creatures living for generations in darkness become white,
pigmentless, and they regain it when exposed to light. For example, the
white, colourless Proteus from the caves of Adelsberg becomes clouded
grey, and ultimately jet black, when kept in a tank whence light is not
strictly excluded.

Blindness is a very general characteristic of creatures which dwell in
darkness. There are all stages between total blindness and weak eyes.
Now, do these blind creatures live in darkness because they are blind,
or have they become first weak-eyed and then blind because of the
continuous disuse of their eyes? The former explanation has actually
been suggested! Individuals not smitten, but spontaneously, as a freak,
born with sore eyes, have crept into the darkness for relief and have
produced a blind race! To carry such a notion to the bitter end leads
to absurdities. Anyhow, it is not understandable where the benefit
of losing the eyesight arises. It can be explained only by continued
disuse: witness _Spalax typhlus_, the blind mole, and, above all, the
Endoparasites.

Let us now take an example to explain the influence of a tangible
external stimulus. Repeated pressure produces callosities. Although
they are not exactly beneficial in the shape of corns on our toes,
they are so on our hands. At any rate, the morphologist can trace the
development of the footpads, nails, hoofs, and horns, step by step from
small beginnings. The cells of the Malpighian stratum, of the inner,
active portion of our epidermis, are excited to extra activity, and
by continually producing more horn cells than peel off the surface of
the skin in the normal process of wear and tear cause the formation
of the pad. It need scarcely be mentioned that hypertrophic growths
are not necessarily useful; they are often harmful, and in that case
pathological.

Lastly, a few words about the very difficult question of _teleology_.
In trying to explain Evolution in a mechanical--sometimes called
monistic, but in reality natural--way, we exclude anything like a
set purpose, a goal, or ideal, a final condition which the organism
strives to attain. Unknown, however, to many morphologists, especially
embryologists, their writings are full of this teleological notion.
Indeed, there are many cases in which an organism becomes changed, and
quickly, too, in a way which cannot but be called reasonable. It starts
modifications, be they outgrowths, alterations in shape or colour, or
the making good of injuries received, which by 'short-cuts' produce
the only advantageous result that can reasonably satisfy the new
requirement or altered circumstances.

Trees growing in precarious positions, after part of the supporting
rock has slipped away, throw out new roots, and rearrange some of
the old ones in the only way which could save the tree. In animals
which have lost part of a limb the wound closes up, and what is left
is turned into a serviceable stump--for example, in water-tortoises
(creatures in which reproduction of lost limbs does not happen). In
frogs and newts the lost part is reproduced, not correctly, but in a
good semblance. Tortoises which have had their shell smashed can throw
off an astonishingly large portion and renew the bone as well as the
overlapping scutes; but this mending is not neatly done. It serves the
requirement, but it is patchwork; the new shell is such as no tortoise
ever possessed before.

Mammals transported into colder countries, or subjected to continued
exposure, grow a thicker coat; and the same kind of tree which in a
sheltered valley is tall, large-leaved, and soft-wooded, assumes a very
different aspect, although perhaps growing into a healthy specimen,
when planted on a wind-exposed hill.

There is no room, or, rather, no time, to apply to these cases the
principle of many variations or the long-continued accumulation of
infinitely small changes. The thing is to be done quickly, or not
at all. Nor can we explain the mending of a wound, which implies an
activity of countless cells, simply as a case of, or similar to, the
reproduction of a lost part; against such an explanation militates the
almost absolute unlikelihood of that precise injury having happened
before to any of the creature's ancestors.

Still, I think we are brought near the solution of the mystery by
such considerations. We see no difficulty in the regeneration of a
few cells, or in the making good of the disturbance suffered by one
of the most simple organisms; but we become suspicious when we see
that countless cells, not of one kind, but of the most varied tissues
and parts of the body, make common cause in remedying a defect in a
serviceable way.

We must assume that since the beginning of life organisms have been
subjected to countless insults. We can scarcely speak of a wound in
an Amæba; but these insults have always been made good, and whenever
this was not the case, that particular organism came to an end. As
these organisms developed into more complicated ones, the possible
insults became more serious, more complicated; and the organisms took
adaptive measures so as to be superior to them. This action, I have
no hesitation in declaring, became by heredity a habit. The whole
creature became so thoroughly 'imbued' (for want of a better word) with
the finding of ways and means for meeting sudden, serious conditions,
that it now acts directly, and produces by a short-cut, with the least
amount of time and with the smallest possible waste of material, that
which meets the occasion, thereby saving the life of the individual
and that of the race. This we cannot but call reasonable and to the
purpose, although it is all carried out by _causæ efficientes_ without
there being any _causæ finales_.




  GEOLOGICAL TIME AND EVOLUTION.


One million years is a stretch of time beyond our conception. We can
arrive at a more or less adequate understanding of what a million
individuals or concrete things means. Several Continental nations
can put more than a million men into the field. We can gaze at a
building which contains as many bricks; and we know that our own body
is composed of millions of millions of cells. No such help applies to
time, because that itself is an entirely relative, abstract conception.
We can imagine what one hundred years are like--a span of time
seemingly short to the hale and hearty octogenarian, enormous to the
child, totally inapplicable to certain animals whose whole life is
crowded into one single day.

Astronomers have long ceased to reckon distances by miles or any
other understandable unit. They express the distances between us and
the stars and nebulæ by 'years of light.' Try to imagine a unit of
length equal to that which is passed through by light (186,000 miles
per second) in one year. Not so very long ago the enormous distances
resulting from astronomical calculations were looked upon as the most
serious objection to the correctness of the astronomers' views as to
the distances which separate our globe from the nearest fixed stars.
We have not yet accustomed ourselves to reckoning time by some similar
broadly-conceived standard--say æons of so many thousand years each.

Unfortunately, we possess no data whatever for calculating the age
of the successive geological strata. Thanks to Lyell, the theory of
violent universal cataclysms has been done away with. It is more
probable that the same agencies have acted which are now changing
the aspect of the globe; and these changes are slow, as far as we
know them--at least, as far as the formation of sedimentary strata is
concerned, and these alone we have to deal with. Various calculations
have been made, based upon the denudation of the mountains, the
filling up of the valleys by the débris, the formation of deltas,
etc. The results give enormous stretches of time, but all of them
unsatisfactory, because the methods are so very local in their
application.

The least objectionable attempt is that which, based upon astronomical
calculations, tried to fix the height of the last Glacial epoch[26] at
about 200,000 years ago, and asserted that since its beginning in the
Pliocene epoch as many as 270,000 years have elapsed. The duration
of the whole Tertiary period has by the same authorities been fixed
approximately at 3,000,000 to 4,000,000 years. Beyond this we cannot
venture without the wildest speculation; but we know to a certain
extent the thickness of the various sedimentary strata, which amount
in all to from 100,000 to 175,000 feet--on the average perhaps 130,000
feet, or about twenty miles.

  [26] James Croll: 'On Geological Time, and the Probable Date of the
  Glacial and Upper Miocene Period,' _Philos. Magazine_, xxxv., 1868, pp.
  363-384; xxxvi., pp. 141-154; 362-386.

Unless we prefer giving up all attempt at calculation as absolutely
hopeless, and thus resign the whole problem, we must at least try to
arrive at some results, and then see if these cannot reasonably be made
use of.

Neither geologist nor physicist, and no zoologist, would accept the
suggestion that these 130,000 feet of stratified rocks have been
deposited within only as many years, although the average rate of
deposit would in that case be not more than 1 foot per year. On the
other hand, an indignant protest is raised against the assumption of
1,000,000,000 years.

Lord Kelvin[27] has come to the conclusion (from data which various
other authorities regard as very unsatisfactory) that not much more
than 100,000,000 years can have elapsed since the molten globe acquired
a consolidated crust. Further time must have passed before the surface
had become stable and cool enough to allow the temperature of the
collecting oceans to fall below boiling-point, and it is obvious that
life cannot possibly have begun until after this had happened.

  [27] William Thomson: 'On the Secular Cooling of the Earth,' _Transact.
  R. S. Edinb._, xxiii., 1864, pp. 157-169.

Wallace, in his 'Island Life,' by making use of Professor A. Geikie's
results as to the rate of denudation of matter by rivers from the
area of their basins, and estimating the average rate of deposition,
concludes that 'the time required to produce this thickness of rock
[Professor Haughton's maximum of 177,000 feet] at the present rate
of denudation and deposition is only 28,000,000 years.' Our lower
assumption of 130,000 feet thickness would give only 20,000,000
years--a rate of 1 foot in 154 years.

Again, if we prefer round numbers to start with, we have only to
assume that the age of the whole Tertiary period, with its 3,000 feet
thickness, is 3,000,000 years (_i.e._, 1,000 feet in 1,000,000 years,
or 1 foot in 1,000 years, surely an excessively slow rate); then
130,000,000 years would bring us to the bottom of the Laurentian or
pre-Cambrian deposits. Of course, it is a pure assumption that the
same rate of destruction and sedimentation applies to the whole of the
strata; but we know nothing to the contrary, especially if we consider
the average periods, the quick periods of extra activity, taken with
the slow periods or those of standstill.

Dana estimated the length of the whole Tertiary period at one-fifteenth
of the Mesozoic and Palæozoic combined. If we take the duration of the
Tertiary period, as before, as 3,000,000 to 4,000,000 years, the total
will amount to from 45,000,000 to 60,000,000 years.

Lastly, Walcott[28] has estimated the duration of the Palæozoic,
Mesozoic, and Cænozoic or Tertiary epochs at about 17,000,000,
7,000,000 and 3,000,000 years respectively, giving 27,700,000 years
from the beginning of the Cambrian; and Williams[29] has calculated the
relative duration of the smaller epochs. See the table on p. 149.

The results of all these calculations fall surprisingly well within
the limits of Lord Kelvin's allowance. Of course they are based upon
assumptions, but none of them is inherently unreasonable; and it
was my purpose to draw attention to the surprising coincidence in
the closeness of these results, perhaps too good to be true. Such
calculations are considered close enough if they range within a few
multiples of each other.

  [28] 'Geological Time as indicated by the Sedimentary Rocks of North
  America.' _Proc. Amer. Assoc. Adv. Sci._, xlii., 1893, pp. 129-169.

  [29] Henry Shaler Williams, 'Geological Biology.' New York, 1895.

Zoologists have fallen into the habit of requiring enormous lengths of
time for the evolution of the animal kingdom. We know that Evolution is
at best a slow process, and the conception of the changes necessary to
evolve man from monkey-like creatures, these from the lowest imaginary
mammals, these from some reptilian stock, thence descending to Dipnoan
fish-like creatures, and so on back into Invertebrata, down to the
simple Monera--this conception is indeed gigantic. Innumerable, almost
endless, slow changes require seemingly unlimited time, and as time is
endless, why not draw upon it _ad libitum_?

Huxley pointed out that it took nearly the whole of the Tertiary epoch
to produce the horse out of the four-toed Eohippos, and that, if we
apply this rate to the rest of its pedigree, enormous times would
be required. This is, however, a very misleading statement, which
necessitates considerable reduction, in conformity with our increased
palæontological knowledge. Animals of the genus Equus--namely,
Ungulata, with one toe, and with a certain tooth pattern--from the
Upper Miocene of India are now known. Moreover, it is not simply a
question of the gradual loss of the side-toes. The change from the
fox-sized little Eohippos and Hyracotherium, so far as skull, teeth,
vertebral column, and limbs are concerned (about the soft parts we know
next to nothing), is a very great one indeed.

Elephants and mammoths seem to have developed very rapidly. None are
known from Eocene strata; but towards the end of the Miocene they had
spread over Asia, Europe, and North America, and that in great numbers.
The Eocene Amblypoda are still so different that we hesitate to connect
them ancestrally with the elephants.

The Pinnipedia (seals and walruses) are strongly modified fissiped
Carnivora, and have existed since at least the Upper Miocene; the
transformation must have been accomplished within the Miocene period.

We cannot shut our eyes to the fact that various groups have from the
time of their first appearance burst out into an exuberant growth of
modifications in form, size, and numbers, into all possible--and one
might almost say impossible--shapes; and they have done this within
comparatively short periods, after which they have died out not less
rapidly. It seems almost as if these go-ahead creatures had, by
accepting every possible modification and carrying the same to the
extreme, too quickly exhausted their plasticity--which, after all,
must have limits--thereby becoming unable to meet successfully the
requirements of further changes in their surroundings. The slowly
developing groups, keeping within main lines of Evolution, and not
being tempted into aberrant side-issues, had, after all, a much better
chance of onward evolution.

A good example of the former are the Dinosaurs. We do not know
their ancestors; but we have here to deal only with their range of
transformation. The oldest known forms occur in the Upper Trias; they
attain their most stupendous development in the Upper Jurassic and in
the Wealden; and they have died out with the Cretaceous epoch. But
already some of their earliest forms had assumed bipedal gait, and the
Oolitic Compsognathus had developed almost bird-like hind-limbs.

On the other hand, there are many instances of extremely slow
development--facts which raise the difficult question of 'persistent
types.' Are these due to a state of perfection which cannot be improved
upon? Or are they due to a kind of morphological consolidation (not
necessarily specialization) which can no longer yield easily, so that
therefore through changes in their surroundings they may come to an end
sooner than more plastic groups?

Struthio, the ostrich; Orycteropus, the Cape ant-eater; Tapirus, and
many others, existed in the Miocene age practically as they are
now; but pre-Pliocene dolphins, cats, monkeys, stags, all belong to
closely-allied and well-defined 'genera,' but different from the living
forms.

Alligators and crocodiles are known from the Upper Chalk; Tomistoma
since the Miocene; Gavialis since the Pliocene.

The oldest surviving reptile is Sphenodon, the Hatteria of New Zealand,
a fair representative of what generalized reptiles of the later
Triassic period seem to have been like; and to the same period belongs
Ceratodus, the Australian mud-fish, hitherto the oldest known surviving
genus of a very ancient and low type so far as Vertebrata are concerned.

Now let us see if the above estimates of geological time are so utterly
inapplicable to animal evolution. On purpose we take one of the lowest
estimates, about 28,000,000 years, and apportion them equally to the
various strata or epochs.

The original owner of the famous Trinil skull, a _Pithecanthropus
erectus_, lived, according to some, in the Late Pliocene, according
to others in the Early Plistocene, period--that is to say, somewhere
about the beginning of our last Glacial epoch, some 270,000 years ago.
Assuming that he and his like reached puberty at sixteen to twenty
years of age, about 17,000 generations would lie between him and
ourselves, or, to put it more forcibly, between him and the lowest
living human races--say the Ceylonese Veddahs. Only 250 generations,
at twenty years, carry us back to 3000 B.C. (_i.e._, beyond
the ken of history); and if it be objected that the differences between
the oldest inhabitants of Egypt, the Naquada, and the present Fellahin
are very slight, we are welcome to multiply these differences sixty
or seventy fold, in order to arrive at the Pithecanthropus level.
But these Naquada had no metal implements, and there cannot be the
slightest doubt that the development of the human race went on by leaps
and bounds after certain discoveries had been made--to wit, the use
of implements and that of fire. That creature which first took up a
stone or a branch and wielded it thereby got such an enormous advantage
over his fellow-creatures that his mental and bodily development went
on apace. The same applies to the improvement of speech. We assume the
single, monophyletic origin of mankind at one place, in one district;
and the differences between some of the races of man are great enough
to constitute what we might call species. Compare the Venus of Milo,
that noble expression of the ancient Greeks' notion of female beauty,
with the 'products of art' of the Veddahs or the dwarfs of Central
Africa, or think of the beau-idéal which a Michael Angelo could
possibly have evolved if he had never seen any but such people.

     _TIME AND EVOLUTION_

  ======================================================================
       I.    |II.|    III.   |    IV.   |       V.     |VI.|    VII.
             |   |           |          |              |   |Generations.
  -----------+---+-----------+----------+--------------+---+------------
             |}  |}          |}         |Adam and Eve  |   |         250
  Recent     |} 5|}          |}         |Man, contem-  |   |       3,500
  Plistocene |}  |}          |}  270,000|  porary with |   |
             |   |}          |}         |  Reindeer    |   |
             |   |}          |}         |  in France   |   |
  Pliocene  -|}  |} 3,000,000|          |_Pithecanthro-| 16|      17,000
             |}  |}          |}  600,000|  pus erectus_|   |
  Miocene   -|}10|}          |}         |Anthropoid    | 10|      60,000
             |}  |}          |}2,100,000| Apes         |   |
  Eocene    -|}  |}          |}         |Lemures       |  5|     420,000
             |   |           |          |              |   |
  Cretaceous | 10|}          | 3,600,000|              |   |
  Jurassic - |  5|}          | 1,800,000|              |   |
  Rhætic    -|}  |}          |}         |Prototheria,  |  3|   1,800,000
             |}  |}          |}         |  or first    |   |
             |}  |} 7,200,000|}         |  Mammalia    |   |
  Keuper    -|}  |}          |}1,800,000|              |   |
  Muschel-   |} 5|}          |}         |              |   |
    kalk     |}  |}          |}         |              |   |
  New Red    |}  |}          |}         |Theromorpha   |  4|     425,000
    Sandstone|   |           |          |              |   |
  Magnesian  |}  |}          |}         |              |   |
    Limestone|}  |}          |}         |              |   |
  Lower Red  |}  |}          |}         |Proreptilia   |  4|     250,000
    Sandstone|}  |}          |}4,000,000|              |   |
  Coal-      |}15|}          |}         |Eotetrapoda   |  4|     500,000
    measures |}  |}          |}         |              |   |
  Mountain   |}  |}17,500,000|}         |              |   |
  Limestone  |   |}          |          |              |   |
  Devonian  -| 15|}          | 4,000,000|Dipnoi and    |  5|   1,000,000
             |   |}          |          |Crossopterygii|   |
  Silurian  -| 10|}          | 2,700,000|First fishlike|  3|     900,000
             |   |}          |          |  creatures   |   |
  Ordovician | 10|}          | 2,700,000|              |   |
  Cambrian  -| 15|}          | 4,000,000|  Sum total of|   |
  Laurentian |   |           |          |   generations|   |   ---------
    Archæan  |   |           |          |   (about)    |   |   5,375,000
    or Meta- |   |           |          |              |   |
    morphic  |   |           |          |              |   |
  ======================================================================

EXPLANATION OF THE TABLE ON P. 149.

  Column I. contains the names of the successive sedimentary strata.

    "   II. contains the percentage of the duration of the various epochs,
  according to _Williams_, the time from the Cambrian until recent times
  being taken as 100.

    "  III. gives the estimated duration in years of the Palæozoic,
  Mesozoic, and Cænozoic periods, according to _Walcott_.

    "   IV. gives in years the duration of the various smaller epochs, as
  computed from Walcott and Williams' statements.

  "      V. Representatives of stages of the ancestral line of man. The
  names stand in the level of the stratum in which they have made their
  first appearance.

    "   VI. contains the number of years which, in the present
  calculation, have been assumed necessary for the animal to reach
  puberty.

    "   VII. contains the number of generations which can have elapsed
  from stage to stage. For example, 60,000 generations separate the
  earliest known anthropoid apes from Pithecanthropus.

Let us follow the descent of man further back. The next stage,
reckoning backwards, is that from Pithecanthropus to _bonâ-fide_
anthropoid apes. They are represented in the Miocene by various
genera--_e.g._, Pliopithecus and Dryopithecus. According to Croll and
Wallace, 850,000 years ago carry us into the Miocene epoch. Assuming
that these apes lived about 600,000 years before Pithecanthropus,
namely, in the later half of the Miocene, and taking puberty at ten
years of age, a high estimate, we get not less than 60,000 generations.

2. From Apes back to lowest Lemurs in the lowest Eocene. The date of
Eocene being fixed at 3,000,000, we have about 2,100,000 years for this
stage; assuming as much as five years for puberty, this results in
420,000 generations.

3. From Lemures to Prototheria. The earliest known mammalian remains
come from the Rhætic, or top formation of the Triassic epoch; allowing
for the Rhætic only 100,000 years, we have to add the whole of the
Jurassic and Cretaceous, in all about 5,500,000 years. Assuming three
years for a generation, we get 1,800,000 generations.

4. From Prototheria to something like the Theromorpha at the bottom of
the Triassic strata. A duration of 1,700,000 years divided by four
gives 425,000 generations.

5. From Theromorpha to Proreptilia, represented by Eryops and Cricotus
from the Lower Permian of Texas. Allowing 1,000,000 years, each
generation at four years, we obtain 250,000 generations.

6. From Proreptilia to Eotetrapoda, the first terrestrial Vertebrata,
represented by something like the Stegocephali, the earliest of which
are known from the Coal-measures. Assuming them to have come into
existence at the bottom of the Coal-measures, for the duration of which
we may guess 2,000,000 years, we get, with four years' allowance for
puberty, 500,000 generations.

7. From Eotetrapoda to a not yet separated or differentiated group
of Crossopterygian and Dipnoan fishes, both of which are known from
Devonian strata. The duration of the latter has been computed at
4,000,000 years, which, with 1,000,000 for the Mountain Limestone
formation, gives us 5,000,000 for this stage. Assuming, for the sake
of round numbers, as much as five years for a generation, we get
1,000,000 generations.

8. Earliest stage, down to the first fish-like creatures. Teeth and
spines indicating the existence of fishes are known from the Upper
Silurian. By carrying the earliest fishes down to the bottom of the
Silurian, with 2,700,000 years' duration, and allowing three years for
attaining puberty, the calculation results in 900,000 generations.

Further back we cannot go. We do not know of any Vertebrate remains
from the Ordovician and Cambrian, which together represent 6,700,000
years, enough for at least half as many generations of Prochordate
creatures. The pre-Cambrian or Laurentian epoch lies quite beyond the
reach of calculation, nor have we any trustworthy fossil remains of
living matter from these strata, to which, however, Haeckel and others
refer the first beginnings of life.

All the above calculations are, of course, only approximate. What we
do know is the existence of representatives of the stages, our proofs
being the fossils; but when we refer the origin of the Eotetrapoda,
for example, to the bottom and not somewhere to the middle of the
Coal-measures, we are guessing merely. Alterations in the levels
assumed for the various stage-representatives will, of course, alter
the result of the number of generations; but the leading idea, as
a whole, is not thereby upset. The fact remains that in the Upper
Silurian we have fishes; from the Coal-measures onwards, fishes and
Amphibia; since the Permian, fishes, Amphibia, and reptiles; since the
end of the Trias these three classes and the Mammalia; and lastly, at
least since the Plistocene, man himself. If Evolution is true at all,
the transformation from early fish-like creatures to man has come about
within these epochs. Being able to assign a time of duration to each
of them, with an approximate total of 21,000,000 years, we are also
able to put the whole ancestral series to a test by expressing each
great stage in generations. The result is very satisfactory. The whole
enormous stretch from the lowest fish-like creatures to man has been
resolved into more than 5,000,000 successive generations, and each of
these means a little step forwards in onward Evolution.

Nothing is to be gained for the understanding of our problem of
Evolution if we multiply this enormous number of generations by ten
or any other multiple. We are not able to conceive changes so small
as those which necessarily have existed between Pithecanthropus and
man if the whole striking difference is analysed into 17,000 steps.
Every one of these stages in the modifications of the muscles, the
skeletal framework, increase of brain, shortening of the trunk,
lengthening of the legs, improvement of the hands, loss of the hairy
coat, etc., is truly microscopical, imperceptible, just as the
Evolutionist imagines the whole process to have been. Again, where is
the difficulty implied by the change from an air-breathing, in many
structural points half-amphibian, fish into a primitive land-crawling
four-footed creature, if we are allowed to resolve the transformation
into 1,000,000 stages? So far from there being any difficulty, rather
does it appear questionable if so many infinitely small changes have
been necessary to bring about this result.

One thousand years make apparently no difference in the evolution of
animals, nor does one second change the aspect of the hands on the
face of a clock, nor did Julius Cæsar's commission of scientific men
appreciate the error of about eleven minutes in the length of the year
beyond its real value; but now the Russians are, owing to this neglect,
nearly two weeks behind the civilized nations.


  THE END.


  BILLING AND SONS, PRINTERS, GUILDFORD.


  By PROFESSOR ERNST HAECKEL


  MONISM;
  OR,
  The Confession of Faith of a Man of Science.

  Translated from the German by J. D. F. GILCHRIST.

  _Crown 8vo., cloth. Price 1s. 6d. net._

'We may readily admit that Professor Haeckel has stated his case with
the clearness and courage which we should expect of him, and that
his lecture may be regarded as a fair and authoritative statement
of the views now held by a large number of scientifically educated
people.'--_Times._

'The Monism, which is the substance of his faith, is thus defined by
him: "Our conviction that there lives one spirit in all things, and
that the whole cognizable world is constituted, and has been developed,
in accordance with one common fundamental law." As the confession
of a distinguished man of science, this little work deserves to be
read.'--_North British Daily Mail._

'This "Confession of Faith" was delivered by the great German
scientist, its author, as an extemporaneous address at Altenburg
rather more than two years ago. There are, no doubt, a large number of
English readers who will welcome a translation, for this "connecting of
religion and science" has long troubled many earnest students of modern
science.'--_Publisher's Circular._

'This is a little book of great daring, an example of the wild
speculative flights of one of the very ablest and greatest of our
contemporary men of science.'--_Aberdeen Free Press._

'The address, whatever we may think of its conclusions, is, however,
most interesting reading, and is admirably done into English by the
translator.'--_Literary World._


  LONDON: ADAM & CHARLES BLACK, SOHO SQUARE.


  _Demy 8vo., price 7s. 6d. net._

  SOURCES OF THE APOSTOLIC
  CANONS.

  _With a Treatise on the Origin of the Readership and other Lower Orders._

  By Professor ADOLF HARNACK.

  Translated by LEONARD A. WHEATLEY.

  _With an Introductory Essay on the Organization of the Early Church
  and the Evolution of the Reader._

  By the Rev. JOHN OWEN, Author of 'Evenings with the Skeptics.'

'Dr. Adolf Harnack is at the present time undoubtedly the leading
liberal authority in Germany on matters connected with early Christian
history.'--_The Times._

'Those who are interested in early Church history know how to prize
anything from the pen of Prof. Harnack. They will not be disappointed
with the present paper, in which, with his accustomed learning and
acute criticism, he annotates and comments upon the fragments of
primitive church law which partly form the basis of the Apostolic
Canons.'--_British Weekly._

'The wide circulation of this volume would be of the happiest augury
for a more scientific and worthy conception of the organization of the
primitive Church.'--Dr. MARCUS DODS in _The Bookman_.



  _Crown 8vo., cloth, price 1s. 6d. net._

  CHRISTIANITY AND HISTORY.

  By ADOLF HARNACK.

  Translated, with the Author's sanction, by THOMAS BAILEY
  SAUNDERS, with an Introductory Note.

'It is highly interesting and full of thought. The short introductory
note with which Mr. Saunders prefaces it is valuable for its
information and excellent in its tone.'--_Athenæum._

'A singularly able exposition and defence of Christianity, as seen in
the newer light, by one of the most learned and acute "evangelical"
critics of Germany. The essay is a masterly one.'--_Glasgow Herald._

' ... We hope the lecture will be widely read.'--_Primitive Methodist
Quarterly Review._

'The lecture itself is weighty in its every word, and should be read
and re-read by those desiring to have in a nutshell the central
positions of modern Christianity.'--_Christian World._


  LONDON: ADAM & CHARLES BLACK, SOHO SQUARE.


  _Third Edition. Crown 8vo., cloth, price 5s._

  SKETCH OF THE HISTORY OF
  ISRAEL AND JUDAH.

  By J. WELLHAUSEN,
  PROFESSOR AT MARBURG.

'This work is now issued for the third time as an independent treatise.
It admirably epitomizes the subject, and exhibits on almost every page
evidences of Professor Wellhausen's profound study.'--_Publishers'
Circular._

'We would only say that those who differ from his critical views will
yet do well to study them, and to read this history in which he applies
them. Its separate publication, in a handy form and at a moderate
price, makes it generally accessible.'--_North British Daily Mail._

'The publication in a separate form of Professor Wellhausen's article
in the "Encyclopædia Britannica" on "Israel" will be very warmly
welcomed by many readers.'--_Manchester Guardian._

'We are very glad to welcome an edition of Professor Wellhausen's
"Sketch of the History of Israel and Judah" in a convenient and handy
form. This is the first time it has appeared in a separate form. It is
already known to students; it ought now to become popular. It is based
on the learned author's studies in Hebrew literature and history, and,
though not controversial in form, it differs totally from orthodox
presentations of the subject.'--_Westminster Review._

'A sketch which has created such widespread and profound interest as
this could not be kept in the pages of a voluminous encyclopædia.
Wellhausen's words necessarily have exceptional importance, even in
the esteem of those who differ from him _toto coelo_.'--_Baptist
Magazine._

'The profound scholarship of the author does not elevate his writing
above the interest of the general reader, and a vivid idea of the
involved Jewish history is obtainable from this volume.'--_Christian
Advocate._


  LONDON: ADAM & CHARLES BLACK, SOHO SQUARE.


  _Demy 8vo., boards, price 3s. 6d. net._

  A CLASSIFICATION OF
  VERTEBRATA,
  RECENT AND EXTINCT.

  With Diagnoses and Definitions, a Chapter on Geographical
  Distribution, and an Etymological Index.

  By HANS GADOW, M.A., PH.D., F.R.S.,

  STRICKLAND CURATOR AND LECTURER ON ZOOLOGY TO THE UNIVERSITY,
  CAMBRIDGE.

'At the end of his work Dr. Gadow adds a useful chapter on the
geographical distribution of the Vertebrata, with a table showing
the approximate number of the known recent species. He also gives
a fanciful though striking calculation to show how some groups are
still in the ascendant, while others are distinctly declining. The
little volume is indeed a welcome addition to the biological student's
library, and it deserves the wide circulation which its author's
eminence is likely to ensure for it.'--_Natural Science._

'It is a book, it need hardly be said, for the student; it is simply
a list of the principal sub-divisions of backboned animals, with just
as much definition as is needed. It may be regarded as an exceedingly
concentrated extract of a full text-book of the vertebrates.'--_Daily
Chronicle._



  _Demy 8vo., cloth, price 21s._

  IN NORTHERN SPAIN.

  By Dr. HANS GADOW, M.A., PH.D., F.R.S.

  _Containing Map and 89 Illustrations._

'Some years back "Wild Spain," one of the best books of its kind,
made you desirous of knowing more of the country. And Hans Gadow has
deepened this feeling in his excellent volume "In Northern Spain,"
and that to an enormous extent. Dwelling at inn or farm, or in their
own tent, they saw the country as it has been seen but rarely, and
they came to know the inhabitants as they can be known in no other
fashion.'--_Black and White._

'To persons visiting the provinces with which the author deals, this
book will be invaluable, and will do more to point their attention to
objects of interest than existing guide-books of Spain, most of which
are out of date.'--_The Field._

'About the best book of European travel that has appeared these many
years.'--_Literary World._


  LONDON: ADAM & CHARLES BLACK, SOHO SQUARE.


Transcriber's Notes

  Variations in spelling, punctuation and hyphenation have been retained
  except in obvious cases of typographical errors.
  Inconsistent hyphenation and spelling are as in the oringinal.
  Italics are shown thus _italic_ and underline thus *underline*.