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VOLUME ELEVEN            NUMBER FOUR

JOURNAL
OF
ENTOMOLOGY
AND
ZOOLOGY

DECEMBER, 1919

PUBLISHED QUARTERLY BY
POMONA COLLEGE DEPARTMENT _of_ ZOOLOGY
CLAREMONT, CALIFORNIA, U. S. A.




CONTENTS


                                                              Page

NOTES ON THE BEHAVIOR OF THE SOCIAL WASP POLISTES
    --_Horace Gunthorp_                                        63

BIOLOGY OF THE NORTH AMERICAN CRANE-FLIES. V. THE
    GENUS DICRANOPTYCHA--_Charles P. Alexander_                67

THE CENTRAL NERVOUS SYSTEM OF NUCULA AND MALLETIA
    --_W. A. Hilton_                                           75


Entered Claremont, Cal., Post-Office Oct. 1, 1910, as second-class
matter, under Act of Congress of March 3, 1879




Journal of Entomology and Zoology

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Notes on the Behavior of the Social Wasp Polistes

HORACE GUNTHORP

Washburn College, Topeka, Kans.


One day last September the writer picked up a nest of the common social
wasp, _Polistes_, which had been detached from its support, and placed
it upon his desk. A short time later he was attracted by a scratching
sound, and discovered that one of the wasps was just beginning to cut
the cap from its cell preparatory to emerging. During the next few days
a series of observations were made and notes taken covering the
behavior of the wasps which emerged from their cells during that
period. Miss Enteman[A] has made a careful study of the instincts of
the social wasps, and while the observations recorded in the present
paper are largely corroborative of her work, some interesting details
are here added.

The cutting of the cap of the cell occupied some time, and extended
around four-fifths of its circumference, the remaining one-fifth being
gnawed and partially chewed through so that it was flexible enough to
act as a hinge for the cap. After the cap was sufficiently cut away,
the wasp started to slowly work itself out, pushing up the top of the
cell like a trap door as progress was made. A good deal of effort was
required to get the body out until the front legs were freed. Then the
wasp had more purchase and progress was somewhat faster until the
second pair of legs came out. After this slight effort seemed to be
necessary for the completion of the operation.

For the next thirty minutes careful observations were made of the
movements of this wasp in order to ascertain its first reactions. It is
evident that they would be somewhat modified from what they are here
recorded if the colony had contained the queen and other workers, as
this specimen had the run of the entire nest, and none of its movements
were effected by those of other individuals. It is equally evident that
all stimuli came from within, or from contact with the nest, and not
from suggestions received from other individuals or from contact with
them. The following is the record made at one minute intervals,
beginning with the time the specimen left its cell:

     8:06. Specimen emerged from its cell.

     8:07. Cleaned its front legs in its mouth and its antennæ
           with its front legs.

     8:08. Moved around some. Rubbed its wings with its hind legs
           and spread them out twice.

     8:09. Cleaned antennæ and front legs.

     8:10. Swung abdomen back and forth, and brushed its wings.
           Moved around the nest rapidly and waved the antennæ,
           but all movements were jerky.

     8:11. Explored nest, occasionally rubbing abdomen with legs.

     8:12. Explored nest.

     8:13. Explored nest. Movements unsteady. Cleaned antennæ and
           front legs.

     8:14. Explored nest, in the course of which it went over the
           edge on to the back side, but immediately returned to
           the under side. Cleaned the front legs and antennæ,
           and then the hind legs.

     8:15. Spread out the wings. Cleaned the antennæ.

     8:16. Cleaned abdomen.

     8:17. Crawled on top or back side of nest again and stayed
           there. Cleaned wings and abdomen.

     8:18. Explored top. Cleaned front legs and antennæ.

     8:19. Stood still. Occasional movement of head, antennæ or
           abdomen.

     8:20. Same as 8:19.

     8:21. Began to explore again, becoming quite lively. Antennæ
           constantly waving.

     8:22. Same as 8:21, but extended its travels to the under
           (cell) side of the nest.

     8:23. Left the nest entirely and began to walk around the
           surface of the desk.

     8:24. Started to climb a bottle that was some six inches
           from the nest. Antennæ still waving.

     8:25. On the neck of the bottle, two inches above the
           surface of the desk. Cleaned front legs and antennæ.

     8:26. Quiet except that it spread its wings once.

     8:27. Still on neck of bottle. Moved its head and antennæ
           back and forth.

     8:28. Slight change in position. Antennæ were still waving.
           Rubbed its wings, spread them, and then rubbed them
           again.

     8:29. Rubbed its hind legs together vigorously.

     8:30. Spread wings once, then rubbed them and the abdomen
           with the hind legs. Rubbed the hind legs together, and
           finally rubbed the right wings vigorously.

     8:31. Moved around some, occasionally stopping to rub the
           right wings.

     8:32. Explored the neck of the bottle.

     8:33. Same as 8:32. Cleaned antennæ.

     8:34. Same as 8:33.

     8:35. Stood still but continued to clean antennæ and front
           legs.

     8:36. Climbed up and explored the cork of the bottle.

     8:37-8:40. Stood still on the cork, occasionally moving its
           jaws.

At 8:40 the nest was placed against the cork and the wasp immediately
crawled onto it, but seemed restless. As the nest has a faint, but
distinct, odor of honey, it was probably attracted to it through the
sense of smell.

The next morning the specimen was nowhere in sight, but forty-eight
hours later it fell out of a loose-leaf binder that had been lying on
the desk. It seemed to be as active as when seen two days before. Some
time during the second night after the appearance of the first
specimen, that is, when it was some thirty hours old, a second
individual emerged. This one was discovered on a pile of books two feet
from the nest where it had evidently crawled soon after emerging.

As soon as the first specimen was rediscovered, that is, when it was
sixty hours old, the second wasp then being thirty hours old, the two
were placed on the nest, and this in turn was placed on a book. They
both started on tours of observation, and every time they came in
contact with each other they made sudden starts and jumps to avoid an
evidently startling new object, meanwhile violently waving their
antennæ and often cleaning these organs after such contact. Dr. Enteman
says, "All wasps possess the instinct of fear. This ... is readily
overcome by the frequent appearance of the awe-inspiring object." This
is true, because they were evidently on familiar terms with each other
in half an hour, and paid very little attention to the frequent
meetings which before had apparently distressed them. They wandered
freely over their nest and the top surface of the book on which it was
placed, but did not attempt to climb off the latter.

At 12 o'clock, four hours later, a third wasp had appeared, and none of
the specimens seemed to be disturbed by the presence of the others.
When the nest was first picked up, one cell containing a well formed
pupa was uncapped. This specimen was then alive, but it may have been
dead at the time of this observation. In either case, it had been
dragged out of its cell, decapitated, and the front legs torn off. No
trace of the head was found, but the body and legs were on the book
about one inch from the nest. Whether this act was connected with the
hunger of the wasps themselves or with the first development of the
instinct of feeding the larvæ in the nest, which Miss Enteman says
begins without imitation, is not clear.

At 2 p. m. (two hours later) the colony was placed out of doors, still
on the book. Two of the wasps soon left the latter, and settled near
it, keeping very quiet for half an hour. The third kept climbing over
and around the nest. At 2:30 one of the two wasps returned to the nest.

At 3 p. m. two of the specimens were on the ground near the porch. They
made only short flights, resembling jumps with the wings assisting,
this being true even when they were disturbed. The third wasp was
beside the colony, chewing on the decapitated pupa, probably getting
some nourishment from it in the process.

During the afternoon the nest was disturbed, and at 6 p. m. all three
specimens had gone from the porch. One was found wandering aimlessly on
a canna leaf near by. It did not seem to be able to fly well. The other
two had disappeared entirely.

The nest was saved and several days later a fourth wasp appeared. It
was a very lively specimen, and spent the first few hours actively
exploring the nest. It seemed of a very nervous disposition, being more
easily disturbed than any of the others had been. Every time the nest
was picked up, it would start for the fingers or forceps holding it. At
one time it was observed with its whole body in a cell, head downward,
evidently examining the interior. After staying close to the nest for a
day, it began to fly around the floor of the room, paying no more
attention to its former home. Even when it was placed on or near it, it
would almost immediately crawl or fly away. Its flying was erratic, and
seemed to lack power, but it got along much better than any of the
other three had done.

From the above observations it would appear that the movements of the
wasp recorded at one minute intervals after emergence from its cell
were probably reactions due to the discomfort of the drying and
hardening of the tissues. At first the wasps apparently had very
little, if any, home instinct. The only things to indicate that they
had any were the facts that the first specimen so readily left the cork
on which it was sitting and went back to its nest when the latter was
held near it, and the fourth wasp stayed on or near the nest for the
first twelve hours. But all the specimens observed left the nest the
first night and showed no intention or disposition to return. The
presence of a second wasp seemed to bring the home instinct into
existence more forcibly, as the first and second wasps stayed with the
nest for six or seven hours when they were returned to it together,
while the fourth one repeatedly left the empty nest almost at once when
it was returned to it. But this instinct was seemingly not very strong,
as they soon wandered away when placed out of doors. They seemed to
have no idea as to how to carry on the work of the colony, but wandered
aimlessly over it. Perhaps this was due to the fact that they were too
young, as Miss Enteman says the development of the nursing instinct is
usually manifested "any time after the first half day of imaginal
life," but was observed in some neuters as young as four hours, while
in others it was delayed for two weeks.

While the above observations are admittedly too few from which to draw
definite conclusions, they seem to warrant the following assumptions,
the first three of which are quoted from Miss Enteman, and hence are
simply corroborative of her work:

     1. "All wasps possess the instinct of fear. This is
        especially strong the first few days after emergence,
        but is readily overcome by the frequent appearance of
        the awe-inspiring object.

     2. "In a sense, the wasp remembers. This is indicated by the
        manner in which it accustoms itself to the sight of
        strange objects, and by its behavior when a change is
        made in its nest or surroundings.

     3. "It shows considerable individual variability, both as to
        time and manner of its response to stimuli."

     4. After emergence, the first reactions are associated
        simply with the discomfort of the hardening of the
        tissues.

     5. It has marked curiosity, as shown by its repeated
        inspection of its nest and other familiar objects.

     6. The "home instinct" seems to be slight when the wasp is
        alone, but becomes stronger when two or more are on the
        same nest.

     7. The olfactory sense is closely associated with the early
        instincts of the wasp.

FOOTNOTES:

[Footnote A: Minnie Marie Enteman. "Some Observations on the Behavior
of the Social Wasps." Pop. Sci. Mo., 61: 339-351, 1902.]




The Biology of the North American Crane-Flies

(Tipulidæ, Diptera)

V. The Genus Dicranoptycha Osten Sacken

BY CHARLES P. ALEXANDER, Ph.D. (Cornell)


GENERIC DIAGNOSIS

_Larva._ Form very elongate, terete; integument smooth, glassy,
transparent; abdominal segments two to eight with a basal transverse
band or area of microscopic chitinized points on the ventral surface;
segment eight with a similar band on the dorsum. Spiracular disk
surrounded by four lobes, the lateral pair more slender than the blunt
ventral pair; dorsal lobe very low or lacking; spiracles small, widely
separated; a triangular brown mark on the disk between the spiracles;
anal gills a fleshy protuberant ring surrounding the anus. Head-capsule
compact, massive, the præfrons large with a few marginal punctures;
externo-lateral plates very broad. Labrum large, flattened, pale;
antennæ two-segmented, the apical segment almost as long as the basal
segment, narrowed to the blunt tip; mandibles with a blunt dorsal and
two blunt ventral teeth; maxillæ generalized in structure; hypopharynx
a rounded cushion; mentum deeply split behind but not completely
divided, with three principle teeth and a small lateral tooth on either
side.

_Pupa._ Cephalic crest low, depressed, setiferous; labrum tumid; labial
lobes oval, contiguous; antennal sheaths ending opposite the base of
the wing. Pronotal breathing-horns microscopic, represented only by
tiny triangular tubercles; mesonotum unarmed; wing-sheaths ending
opposite the middle of the third abdominal segment; leg-sheaths ending
opposite the base of the fifth abdominal segment, the tarsi terminating
on a level, or nearly so. Abdominal tergites and sternites each with
four transverse rows of microscopic setæ; lateral spiracles on segments
two to seven.


DISCUSSION OF THE GENUS

The genus _Dicranoptycha_ was erected by Osten Sacken in 1860 (Proc.
Acad. Nat. Sci. Phila. for 1859, p. 217). The genus includes a small
group of crane-flies with a Holarctic distribution, there being about
six species in North America and two, or possibly three, in Europe. As
I have indicated elsewhere, _D. signaticollis_ v.d.W. of Java is
undoubtedly a species of _Libnotes_. Of the American species, _D.
germana_ O.S. is characteristic of the Canadian life-zone of
northeastern America. _D. sobrina_ O.S. is widely distributed in the
United States and southern Canada, usually occurring in the
Transitional and Upper Austral life-zones. So far as known at present
it is the only species of the genus occurring on the Pacific slope. The
remaining American species (_nigripes_ O.S., _winnemana_ Alex.,
_tigrina_ Alex. and _minima_ Alex.) are Austral in distribution,
occurring in the southeastern and south central United States. A more
detailed account of the distribution of the species is given in another
paper by the writer which may be consulted (Proc. Acad. Nat. Sci.
Phila. for 1916, pp. 496, 497). All of the known species are generally
similar to one another in appearance and are separated by relatively
slight differences of size, color and structure.

Nothing has ever been written concerning the immature stages of this
peculiar group of crane-flies. The species described hereinafter were
reared at Lawrence, Kansas, and the general conditions under which they
occur may be briefly discussed:

North Hollow, on the Campus of the University of Kansas, is a typical
dry Austral woodland traversed by a small stream that is entirely dry
during the months of midsummer drought. The soil consists of a rich
black humus that is soft and mellow except during the period of
greatest dryness, being overlain by a varying depth of vegetable debris
and leaf-mold. It is in this relatively dry soil that the larvæ of
_Dicranoptycha_ occur. The forest cover consists of Carolina poplar,
_Populus deltoides_ Marsh; black walnut, _Juglans nigra_ L., white elm,
_Ulmus americana_ L.; Kentucky coffee-tree, _Gymnocladus dioica_ (L.)
Koch; honey locust, _Gleditsia triacanthos_ L.; red bud, _Cercis
canadensis_ L.; yellow wood, _Cladrastis lutea_ (Mx.f.) Koch;
tree-of-heaven, _Ailanthus glandulosa_ Desf., etc. The principle shrubs
are the goose-berry, _Ribes gracile_ Mx.; poison ivy, _Rhus
Toxicodendron_ L.; wahoo, _Evonymus atropurpureus_ Jacq.; bladder-nut,
_Staphylea trifolia_ L.; coral-berry, _Symphoricarpos orbiculatus_
Moench.; blackberried elder, _Sambucus canadensis_ L., etc. The herbage
is made up of tall grasses, composites and, in the spring, the
all-dominant cleavers, _Galium_. In addition to the above, great
tangles of lianas (_Smilax_, _Vitis_, _Ampelopsis_, etc.) are found.

In situations such as the above these Austral species of
_Dicranoptycha_ spend their entire lives. The first larvæ of _D.
winnemana_ were found here on March 20, 1918, by the writer and his
wife. At this time they were well grown (length 16 mm.; diameter 0.9
mm.). They occurred just beneath the cover of fallen leaves and other
debris in the upper layers of soil. Here they were associated with pupæ
of _Tipula angustipennis_ Lw., larvæ of _Sciara_ (Mycetophilidæ);
_Psilocephala hæmorrhoidalis_ Macq. (Therevidæ), numerous beetle larvæ,
centipedes, etc. By their elongate form and glabrous shiny skin they
are very characteristic and easily recognized. The glassy appearance of
the body suggests the shiny shells of a small coiled molluscan whose
dead fragments occurred in some numbers in the same situations. These
larvæ were placed in rearing and the first adults appeared in the
breeding-cages on May 6, and from that time on continued to appear in
large numbers. It was over a month later that the first individuals
were taken in the field. The pupal duration could not be determined
closer than ten days, and this may be the usual length of time required
for this stage. The first larvæ of _D. minima_ were found on July 2,
1918, in similar situations in North Hollow. At this time they were
only about one-half grown. On July 11 much larger larvæ of this species
were secured and placed in rearing, emerging as adults on July 21. The
larvæ, like these of _D. winnemana_, live just beneath the layer of
leaf-mold in the upper zone of black soil. They are usually quite
sluggish in their motions but at other times are quite active. The
larvæ are herbivores and feed on the rich organic earth in their
haunts. When ready to pupate, they encase themselves in earthen cells
(10 mm. × 3.5 mm.), firm in texture, rather thick-walled but without
silk. There is a small opening at either end. The length of the cavity
is but little greater than the pupa itself. In this cavity the pupa
rests and matures. As in other insects, the teneral pupæ are very pale
yellow but gradually darken in color until, at emergence, they are of a
dark brownish-black. When newly transformed the teneral flies rest on
the ground and on the leaves of low plants nearby.

The adult flies of _D. germana_ usually occur in the immediate
neighborhood of running or stagnant water and may be swept from the
rank vegetation in such places. The flies rest on the upper surface of
the leaves of tall herbs and low shrubs. In eastern Kansas, the flies
of _D. winnemana_, _D. tigrina_ and _D. minima_ often occur together.
In June, _D. winnemana_ appears on the wing and is found associated
with _Tipula morrisoni_ Alex., _T. mingwe_ Alex., etc.; in July, _D.
minima_ appears, together with _Tipula flavibasis_ Alex., _T.
unimaculata_ Lw., etc.; still later in July _D. tigrina_ emerges and
all three species fly together during August and into September when
they fly with _Tipula ultima_ Alex., _T. unifasciata_ Lw., etc. It is
curious that no other species of Limnobiinæ occur in the thamnophytic
association frequented by _Dicranoptycha_. All three species of this
genus as discussed above have habits that are generally similar to one
another. They are usually found resting quietly on the upper surface of
the leaves but fly readily and on slight disturbance. Pairs in
copulation are often found resting, the bodies directed away from one
another and the wings folded over the abdomen. While thus united they
fly readily, sometimes the female taking the initiative, sometimes the
rather smaller male. The eggs are deposited in the soft earth in these
situations.


NATURAL AFFINITIES

In the Monographs (1869) Osten Sacken included the genus
_Dicranoptycha_ in his tribe (section) Limnobina anomala, or, as it
subsequently became known, the Rhamphidini, and still later the
Antochini. A recent survey of the immature stages of several Antochine
genera has shown that the tribe is merely an artificial grouping based
on superficial resemblance of the adult flies. This heterogeneous
assemblage includes representatives of at least three other tribes,
_Dicranoptycha_, together with _Antocha_, _Elliptera_, _Rhamphidia_,
etc., showing an undeniable affinity with the Limnobiini, whereas
_Teucholabis_, _Elephantomyia_, etc., show an equally clear
relationship with the Eriopterini. Moreover a close phylogenetic
relationship with the lowermost subtribes of the Hexatomini (_Ularia_,
_Epiphragmaria_, etc.), is easily apparent.

_Dicranoptycha_ shows the closest affinities with _Antocha_ and
_Rhamphidia_. The larvæ of these three genera, each of which typifies a
division, show the following common characters:

Abdominal segments with basal transverse creeping welts or areas of
microscopic points. The massive compact head-capsule with the
præfrontal sclerite large, distinct, the externo-lateral plates large,
mussel-shaped and very thin. The mentum is not completely divided
medially. The maxillæ are large and of primitive structure, the
cardines and stipites distinct, the two distal lobes large, subequal in
size, covered with hairs and bearing sensory organs. Mandibles with one
or more dorsal and two or more ventral teeth in addition to the apical
point.

The differences between these allied divisions are best indicated by a
key.


LARVAE

     1. Spiracular disk with only the two long ventral lobes
        remaining; spiracles lacking or vestigial; abdominal
        segments with both dorsal and ventral welts; strictly
        aquatic.
                                                    _Antocharia._
        Spiracular disk surrounded by four or five short lobes;
        spiracles large and functional; abdominal segments with
        ventral welts only (except the dorsum of segment eight);
        terrestrial or semiaquatic.

     2. Body moderately elongated and covered with a long dark
        pubescence; spiracular disk squarely truncated,
        surrounded by five subequal stout lobes; mentum with
        five subequal teeth, the lateral one of either side not
        conspicuously reduced.
                                                  _Rhamphidaria._

        Body very long and slender, glabrous; spiracular disk
        obliquely truncated, surrounded by four slender naked
        lobes; mentum with three subequal primary teeth and a
        much reduced lateral tooth on either side.
                                              _Dicranoptycharia._


PUPAE

     1. Pronotal breathing-horns branched; aquatic.
                                                    _Antocharia._

        Pronotal breathing-horns not branched; semiaquatic or
        terrestrial.

     2. Pronotal breathing-horns distinct, elongate-cylindrical.
                                                  _Rhamphidaria._

        Pronotal breathing-horns apparently lacking, microscopic.
                                              _Dicranoptycharia._


THE SUBTRIBE DICRANOPTYCHA

A Key to the Species of Dicranoptycha


LARVAE

     1. Spiracular disk with the dark markings less extensive;
        the mark of the lateral lobes not contiguous with the
        spiracle or the triangular area on the disk; dorsal
        marking indistinct or lacking.
                                             _D. winnemana_ Alex.

        Spiracular disk with the dark markings more extensive;
        the mark of the lateral lobes suffusing the ventral inner
        margin of the spiracle and usually closely approximated
        or nearly contiguous with the triangular area on the
        disk; dorsal marking black, transversely rectangular.
                                                _D. minima_ Alex.

     Description of the Species.


DESCRIPTION OF THE SPECIES

1916 _Dicranoptycha winnemana_ Alexander; Proc. Acad. Nat. Sci. Phila.,
pp. 500, 501; Pl. 25, fig. 12.

_Larva._--Length, 20-22 mm.
          Diameter, 0.9-1.1 mm.

Coloration varying from white to almost black depending on the nature
and amount of the food eaten which shows clearly through the
transparent integument. The fat-bodies likewise show through and give a
white color to the larva especially after death.

Form very elongate (fig. 1), body terete; integument very glabrous,
transparent and glassy. Prothoracic segment a little longer than the
mesothorax which, in turn, slightly exceeds the metathorax. The
intermediate abdominal segments are elongated. The basal ring of
sternites two to eight bears a transverse band or area of microscopic
chitinized spicules, the one on the eighth segment split lengthwise by
a capillary line. A similar band occurs in the same position on the
dorsum of the eighth segment but the pleural region is devoid of such a
band.

Spiracular disk (fig. 8) moderate in size, obliquely truncated,
surrounded by four lobes, a pair of small, slender, lateral lobes and
short, broader ventral lobes. The usual dorso-median lobe is lacking
but its position is indicated by a gently rounded convexity. The inner
face of the lateral lobe bears a narrow semi-lunate black mark with the
concavity toward the spiracle, the proximal end acutely pointed. The
ventral lobes bear a similar but smaller subrectangular black mark. A
pale and usually indistinct dusky mark occupies the inner face of the
dorsal lobe. On the disk between, and slightly below the level of, the
spiracles is a large brown triangular or V-shaped mark. The spiracles
are small, separated from one another by a distance equal to about 2.5
to 3 times the diameter of one; the center-piece of the spiracle is
black, the ring yellow surrounded by an outer dusky margin. Anal gills
fleshy and protuberant as a blunt ring surrounding the anus (fig. 10).

Head-capsule (fig. 2) of the compact, massive type of the Limnobiini;
præfrontal sclerite (fig. 3) large and distinct; the sclerite broad
with the sides subparallel to about midlength, thence tapering
gradually to the tip which is entire; there are two or three punctures
at the margin before midlength. Interno-lateral plates narrow, a little
longer than the præfrons; externo-lateral plates very broad, thin and
flattened with the posterior margin very obtuse and the inner ventral
portions continuous with the mental plate. Labrum (fig. 3) very broad
and extensive, flattened, pale in color, the anterior margin with about
two sense-organs. Mentum (fig. 4) deeply split behind but not
completely divided, the anterior margin with three primary teeth that
are subequal in size or the middle one a little smaller; a much reduced
lateral tooth on either side. Præmentum smaller than the hypopharynx,
in outline roughly oval or semicircular with the two labial palpi
surrounded by hairs at the base. Hypopharynx (fig. 5) consisting of two
chitinized arms that are contiguous but not fused medially, the
concavity between them filled with a rounded cushion that is covered
with tubercles arranged in more or less distinct oblique parallel rows.
Antennæ (fig. 6) two-segmented, the basal segment cylindrical with an
auditory plate on the face at beyond midlength; apical segment long and
slender, in length but slightly less than the basal segment, tapering
gradually to the bluntly rounded apex. Mandibles (fig. 7) simple with
the teeth blunt; apical point longer than the lateral teeth; dorsal
tooth single, broad, very flattened and obtusely pointed; ventral teeth
two, a little smaller than the dorsal tooth. Maxillæ (fig. 2) of a
generalized structure, the cardines distinct and feebly chitinized;
distal lobes of the organ consisting of a subequal inner and outer
lobe; the outer lobe with an abundance of long, delicate hairs and
bearing a few sensory papillæ including one larger palpiform organ.

_Pupa._--Length, 9.1-12.8 mm.
Width, d.-s., 1.6-1.8 mm.
Depth, d.-v., 1.6-1.9 mm.

Thoracic dorsum shiny light brown; in very old pupæ the color is much
darker, but still retains a much brighter color than the leg and
wing-sheaths; abdomen pale becoming darker in age, especially on the
pleura.

Cephalic crest (fig. 13) low and depressed, inconspicuous, lying
between the antennal bases which extend beyond it; there are four small
setigerous lobes, the larger pair of which are posterior in position.
Front between the eyes broad, subparallel. Two blunt tubercles on
either side of the forehead. Eyes large, with coarse ommatidia. Labrum
semicircular in outline, tumid. Labial lobes large, oval, contiguous
with one another, at the tip of the labrum. Maxillary palpi moderately
long and slender, nearly straight, gradually narrowed to the tip which
ends opposite the knee-joint of the fore legs. Antennæ with the basal
segments separated only by the cephalic crest, the sheaths ending about
opposite or a little before the lateral angle of the thorax.

Pronotal breathing-horns (fig. 14) very small, almost microscopic; when
viewed from the dorsal aspect appearing as tiny triangular tubercles.
Mesonotum moderately convex, unarmed, the V-shaped suture distinct; a
few setæ on the mesonotum, including one near the end of each scutal
lobe. Wing-sheaths rather short, but narrow, ending about opposite
midlength of the third abdominal segment. Leg-sheaths ending opposite
the base of the fifth abdominal segment, the tips of the tarsi ending
about on a common level or those of the fore legs a trifle longer.

Abdominal segments (fig. 11) subdivided into four annuli that bear
transverse bands of microscopic setæ; these bands increase in width
from the basal to the apical. Spiracles on the pleural region of
segments two to seven, lying opposite the third annulus and close to
the ventral margin of the pleura. No spiracles are discernible on the
dorsum of the eighth segment. Male cauda (fig. 11) with the ventral
lobes very blunt, rounded; the dorsal lobes very small, terminating in
a sharp spine that is directed dorsad and bears a weak seta near its
base. Female cauda (fig. 12) with the ventral lobes a little longer
than the dorsal lobes; the latter at the outer angle of the apex with a
short stout spine that is directed dorsad as in the male.

     _Nepionotype_ (type larva), Lawrence, Kansas, April 2, 1918.

     _Neanotype_ (type pupa), with the type larva, May 6, 1918.

     _Paratypes_, larvæ and pupæ, about fifty from the type
     locality, March 20 to May 20, 1918.


_Dicranoptycha minima_ Alexander.

1919 _Dicranoptycha minima_ Alexander; Ent. News, Vol. 30.

The larva is very similar to that of _D. winnemana_ as described above,
but is slightly smaller. The spiracular disk (fig. 9) has the dark
markings much more extensive. The mark of the lateral lobes is
contiguous with the spiracles and is also closely approximated to the
large triangular brown mark on the disk. There is a large transverse
rectangular mark occupying the inner face of the dorsal lobe. The
marking of the ventral lobe is about as in _D. winnemana_.

     _Nepionotype_, Lawrence, Kansas, July 11, 1918.

     _Neanotype_, Lawrence, Kansas, July 21, 1918.

     _Paratypes_, a few larvæ from the type-locality.


Explanation of the Figures

A--Labial Lobes; E--Eye; EL--Externo-lateral Plate; G--Anal Gills;
IL--Interno-lateral Plate; Lb--Labrum; M--Maxillary Palpus; P--Pronotal
Breathing-horn; Pf--Præfrons; S--Spiracle.

Fig. 1. Larva of _Dicranoptycha winnemana_, ventral aspect of body.

Fig. 2. The same, head-capsule, ventral aspect.

Fig. 3. The same, head-capsule, dorsal aspect.

Fig. 4. The same, mentum, ventral aspect.

Fig. 5. The same, hypopharynx, ventral aspect.

Fig. 6. The same, antenna.

Fig. 7. The same, mandible.

Fig. 8. Larva of _Dicranoptycha winnemana_, spiracular disk,
        dorso-caudal aspect.

Fig. 9. Larva of _D. minima_, spiracular disk, caudal aspect, the anal
        gills protruded.

Fig. 10. Larva of _D. winnemana_, spiracular disk, lateral aspect.

Fig. 11. Pupa of _D. winnemana_, lateral aspect of male.

Fig. 12. The same, lateral aspect of female cauda.

Fig. 13. The same, head and mouth-parts, ventral aspect.

Fig. 14. The same, pronotal breathing-horn, enlarged.

[Illustration]

[Illustration]




The Central Nervous System of Nucula and Malletia

WILLIAM A. HILTON


These bivalve forms are grouped among the simplest of the molloscs. It
is especially from the condition in _Nucula_ as described by Pelseneer
'91, that the conception of the most anterior ganglion being composed
of four ganglia, has its chief support. Drew '01, who has also studied
_Nucula_, believes that the lobes of the ganglion in _Nucula_ are
superficial and that the four connectives coming from the ganglion may
be interpreted in another way. That is, that one pair of nerves may
represent an otocystic branch partly fused with the connective. This
view seemed reasonable to him as Stempel '99 in _Solenyma_ found the
otocystic nerves arose directly from the cerebral ganglion.

The two species of this group used for study were collected at Laguna
Beach. _Nucula castrensis_ Hinds, occurs abundantly at low tide under
rocks. It is rather small for dissection, but very good complete series
were obtained and stained in hematoxylin. _Malletia faba_ Dall, was
much less abundant. Specimens were obtained from holdfasts or from
dredging. Although this was a larger species, gross dissection was not
very easily carried out on any of the specimens, but good series were
made.

The ganglia of _Nucula_ are easily studied in section. The cerebral
mass seems composed of one main mass, partly divided into four
subdivisions, the two central most completely fused, and the lateral
quite distinct in places. The central portion might represent the
cerebral ganglia and the lateral, the pleural if we take that
interpretation. The pedal ganglion is made of right and left parts
quite completely fused except at the margins. The pedal mass is the
smallest of the three chief ganglionic areas. The visceral ganglia are
quite widely separated and a little larger than the pedal mass.

The ganglia of _Malletia_ are in general plan similar to those of
_Nucula_, the greatest differences being in the cerebral mass. The
cerebro-pleural mass seems almost one. In most sections it is very
compact and a little more complicated in structure than the ganglion of
_Nucula_. However there are two small ventral ganglionic branches or
small ganglia attached to the ventral side of the cerebral mass. These
small ganglia may represent the visceral. Farther back in a cross
section series as the cerebral mass disappears two other small branches
take origin and run parallel to the nerves from the ganglionic cords.
These two branches on each side seem to run together before the pedal
ganglia are reached. Neither of these pairs of nerves seems connected
with an otocyst.

At the cephalic end of the cerebro-pleural ganglion the large
ganglionic cords are in evidence. A little distance from the cephalic
end on the dorsal side there are quite large groups of cells down from
the surface and surrounded by nerve fibers. The course of the fibers
here is quite complex. On the ventral lateral sides of the ganglia are
paired light areas of fibers which may be traced into the fibers of the
ganglionic cords.

The pedal ganglion is small and much as in _Nucula_. The visceral
ganglia are larger and widely separated.

In both _Nucula_ and _Malletia_ young specimens were used for study. In
_Nucula_ there was more the appearance of four ganglia in the
cerebro-pleural mass, and the ganglia seem less complex than in
_Malletia_. This last species has more separate pleural ganglia, if the
ganglionic cords can be so regarded.

In neither of the species studied were all parts of the connectives
easy to follow, so it was impossible to test the suggestions of Drew,
but in both species there is some indication of two lateral lobes of
the cerebral mass, and in _Nucula_ there is good evidence of two
central ganglia as well as the smaller lateral ones. The lateral
ganglia of the cerebral mass are most clearly separated in _Malletia_.
In _Nucula_ the lateral ganglia are larger in proportion and the
distribution of the gray and white matter is more irregular.


REFERENCES

_Drew, G. A._                            1901

The life history of Nucula delphinodonta. Quart, jour. sc.
vol. 44, pt. 3.

_Pelseneer, P._                          1891

Contribution á l'étude des Lamellibranchs. Arch. d. biol. xi.

_Stempell_                               1899

Zur Anatomie von Solrmya togata. Zool. Jahrb. Bd. xiii.
(_Contribution from the Zoological Laboratory of Pomona College_)


EXPLANATION OF FIGURES

Fig. 1. Diagram of the ganglia of _Nucula castrensis_, reconstructed
from serial sections. The probable position of the connectives is shown
and the proportionate distances between ganglia are given. The upper
ganglion is the cerebro-pleural with large nerves leading off from the
ganglion which is itself lobed into four chief lobes. The pedal
ganglion is next. In section the pedal ganglion at one place seems to
be made up of four parts which may correspond to four connectives from
the cerebro-pleural although only one pair of connectives was clearly
determined. The visceral ganglion is connected with the pedal below.
×70.

Fig. 2. Cross section of cerebro-pleural ganglion. On the right side
one of the lateral ganglia is shown. The one of the other side does not
show because the section is not straight across. The dorsal side is up.
×300.

Fig. 3. Section of the pedal mass of _Nucula_, through the center. The
dorsal side is up. ×300.

Fig. 4. Left side of the visceral mass of _Nucula_. Dorsal side up.
×300.

Fig. 5. Nerve cells from the central nervous system of _Nucula_. ×450.

Fig. 6. Section through the body of _Nucula_ showing the position of
the cerebro-pleural ganglion cut through the center. Dorsal side up.
The cellular portion of the ganglion is black. ×70.

Fig. 7. Section through the body of _Nucula_ at the level of the
visceral nerves which are shown on either side of the section. The area
of nerve cells is shown in black. ×70.

Fig. 8. Reconstruction from serial sections of the cerebro-pleural mass
nerves and connectives of _Malletia faba_. The drawing is a ventral
view, the cephalic side is at the top. ×70.

Fig. 9. Reconstruction of pedal ganglion of _Malletia_ from the ventral
side. Cephalic side at the top. ×70.

Fig. 10. Reconstruction of visceral ganglia of _Malletia_. ×70.

Fig. 11. Section through cerebro-pleural mass of _Malletia_. The dorsal
side is up. On the ventral side to the left and right are the
beginnings of the lateral lobes or ganglionic cords which may represent
the pleural ganglia. In this species the cerebral ganglia are not
separated into right and left halves as in _Nucula_. ×300.

Fig. 12. Section through the central part of the pedal mass of
_Malletia_. The dorsal side is up. ×300.

Fig. 13. Section through one visceral ganglion of _Malletia_. The
dorsal side is up. ×300.

[Illustration]

[Illustration]




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Transcriber's Notes


Page 64: Changed * * * to ... (preferred form for ellipsis).
  Originally: This * * * is readily overcome by the frequent

Page 64: Changed "placd" to "placed".
  Originally: surface of the book on which it was placd,

Page 68: Changed "X" to "×".
  Originally: cells (10 mm. X 3.5 mm.)

Page 70: Changed "chitinizd" to "chitinized".
  Originally: Changed area of microscopic chitinizd spicules,

Page 71: Changed "Lengh" to "Length".
  Originally: Pupa.--Lengh, 9.1-12.8 mm.

Page 75: Retained "molloscs", as a possible spelling variant for
"molluscs". However, it may be a typo.
  Originally: forms are grouped among the simplest of the molloscs.

Pages 75, 76: Retained "Stempel" and "Stempell" spelling variations.

Page 76: Changed "once" to "one".
  Originally: the pedal ganglion at once place seems to be made up

Page 76: Changed all instances of "X" to "×" to indicate magnification.