VOLUME ELEVEN        NUMBER TWO

JOURNAL

OF

ENTOMOLOGY

AND

ZOOLOGY

JUNE, 1919

PUBLISHED QUARTERLY BY

POMONA COLLEGE DEPARTMENT of ZOOLOGY

CLAREMONT, CALIFORNIA, U. S. A.

CONTENTS

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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[Pg 27]

Annelids from Laguna Beach

This list includes specimens recently determined by Dr. R. V. Chamberlin, but
does not include new species reported on at that time.

(Contribution from the Zoological Laboratory of Pomona College)

[Pg 28]

Structure of Dolichoglossus Pusillus

ALMA EVANS

The animals were studied from serial sections cut in several planes. The stains
used were carmine, hematoxylin and eosin. The hematoxylin seemed to show the
tissues more clearly. A graphic reconstruction was attempted, but did not prove
satisfactory because of the individual artificial foldings and contractions. The drawings
were obtained by the use of a camera lucida. The general drawings,
Figs. 1–9
inclusive, are not filled in in great detail. The special drawings are shown at greater
magnification with more of an attempt to show the actual condition.

Dolichoglossus is a soft worm-like animal with ciliated surface. It is divided
into three distinct regions: the proboscis, a long club-shaped organ; the collar, a
fold in the surface just behind the proboscis, and the trunk, a long cylindrical portion
posterior to the collar.

Dolichoglossus is a marine form living in sandy bays or sheltered places. Mucous
glands in the surface epithelium secrete a sticky fluid which covers the body and to
which tiny sand grains stick. The sand clinging to the mucous coated surface forms
a fragile temporary tube in which the animal is usually secluded. The animals in
the living condition are bright orange or red but lose their color very soon after
preservation in alcohol or formalin.

The proboscis cavity extending the entire length of the organ is surrounded by a
network of connective tissue supported by longitudinal bands of plain muscle. This
cavity is supposed to communicate with the exterior by a very small opening, the proboscis
pore, but this did not show in the specimens examined. The heart, proboscis
gland and notochord are located in the posterior part of the proboscis.

The collar contains the central nervous system, part of the notochord, the dorsal
blood vessel, ventral and dorsal mesenteries, mouth opening and anterior part of the
alimentary canal.

The trunk contains the alimentary canal, dorsal and ventral blood vessels, dorsal
and ventral nerves, the gill-slits, the reproductive bodies, dorsal and ventral mesenteries
and muscle bands.

The nervous system consists of three parts: the central, located in the collar
region, Fig. 5; the sub-epidermic network extending over the entire body just under
the surface epithelium, Figs. 1
–7; and the dorsal and ventral strands which are thickenings
of the sub-epidermic network extending throughout the trunk, Figs. 1 and 7.
There is also quite a decided thickening of the sub-epidermic network at the base of
the proboscis, Figs. 5, 6.

The vascular system consists of two parts, the central and the peripheral. The
central is made up of the heart, a thin-walled vesicle at the base of the proboscis
just dorsal to the notochord, and connected with it the proboscis gland, a plexus of
capillaries just anterior to the notochord. Fig. 5. The peripheral system is composed
of a ventral and a dorsal vessel. The dorsal starts at the heart and continues
just ventral of the dorsal nerve throughout the length of the body. Figs.
1, 5, 7. The
ventral vessel extends from the posterior border of the collar to the anal end. It is
connected with the dorsal vessel by a circular vessel in the posterior edge of the collar.

The mouth is situated ventrally at the base of the proboscis, within the collar,
[Pg 29]
and opens directly into the straight alimentary canal. The latter is a straight tube
extending from the mouth opening to the anus. Figs. 5, 1,
7, 9.

The alimentary canal in the anterior part of the collar gives off a diverticulum,
which grows forward and supports the proboscis. Because this diverticulum has the
vacuolated appearance of the notochordal tissue of higher animals, it has been regarded
as a notochord. It is largest at the base of the proboscis immediately anterior
to the heart. Figs. 5, 6.

The paired gill-slits occupy the region just posterior to the collar. They are
arranged in two longitudinal grooves in the dorsal wall. The number increases
throughout life, new slits appearing just behind those already in place. I found
about twenty-five to be the average number, while particular individuals had as low
as eighteen and twenty and as high as thirty and thirty-one. The gills are formed
in the shape of a U. A skeletal rod or gill bar separates the gills from each other.
The gills are supplied with blood from the dorsal vessel. Figs.
3, 7, 8.

The sexes are distinct. The ovaries and testes are saccular organs arranged in
a row along the gill and succeeding region. The sacs in other genera, for example
Balanoglossus as described by Shipley, open directly on to the epidermis. I have been
unable to see these openings in my preparations. Fig. 8 shows the position of the
ovaries in the female; the testes in the male are in a similar location.

The surface epithelium is modified ciliated columnar, varying slightly in thickness,
size of nuclei and size and shape of cell according to location. Figs.
13, 14, 15.

The epithelium forming the gills and intestine is also modified ciliated columnar.
That of the gills having short narrow cells and small nuclei, and that of the intestine
having longer thicker cells and large nuclei. Figs. 11, 10.

The connective tissue surrounding the proboscis cavity is of a peculiar arrangement.
The connective tissue itself consists of fine strands loosely interwoven, but
arranged in a definite manner. The strands form a fine network which gives a beautiful
lacy appearance. Small round nuclei are quite numerous in connection with the
strands. Longitudinal bands of plain muscle are very conspicuous in the connective
tissue. These muscle bands are probably used in altering the size and shape of the
proboscis. Figs. 4, 20, 21.

The nervous tissue consists of many fibers thickly interwoven. There are a few
small nuclei scattered about among the fibers. Figs. 12, 13.

The muscle is unstriated. The fibers are very long in some places, shorter in
others and always quite distinct.

(Contribution from the Zoological Laboratory of Pomona College)

REFERENCES

[Pg 30]

EXPLANATION OF FIGURES

Fig. 1. Cross section through the gill region showing gill opening. D. N., dorsal
nerve. D. V., Dorsal vessel. G. O., gill openings. A, alimentary corps. G., gill.
V. N., ventral nerve. V. V. ventral vessel. N., nervous tissue. ×40.

Fig. 2. Cross section through the base of the proboscis showing diverticulum wall
and proboscis gland. D., diverticulum. N., nervous tissue. P. G., proboscis gland.
×40.

Fig. 3. Longitudinal section through a gill opening. N., nervous tissue. G., gill.
G. O., gill opening. ×40.

Fig. 4. Cross section through the center of the proboscis. N., nervous tissue.
M. C., muscle in the connective tissue. T., connective tissue. ×90.

Fig. 5. Longitudinal section through the base of the proboscis and collar. M.,
mouth. C. N., central nervous system. H., heart. No., notochord. P. G., proboscis
gland. N., nervous network. A., alimentary canal. D. V., dorsal ventral. ×40.

Fig. 6. Cross section through the base of the proboscis showing thickened nerve
network. N., nerve network. D., diverticulum wall. H., heart. ×40.

Fig. 7. Cross section through gill region. D. N., dorsal nerve. D. B. V., dorsal
blood vessel. G. B., gill vessel. V. N., ventral nerve. V. V., ventral vessel. ×40.

Fig. 8. Longitudinal section through the gill region. G., gills. B., blood. O.,
ovary. N., nervous network. ×40.

Fig. 9. Cross section of alimentary canal. A., wall of alimentary canal. ×40.

Fig. 10. Intestinal epithelium, modified ciliated columnar. ×400.

Fig. 11. Epithelium of the gill, modified ciliated columnar. ×400.

Fig. 12. Nervous tissue. ×400.

Fig. 13. Surface epithelium of proboscis, modified ciliated columnar. ×400.

Fig. 14. Surface epithelium of collar, modified ciliated columnar. ×400.

Fig. 15. Surface epithelium of trunk, modified ciliated columnar. ×400.

Fig. 16. Cells of testis. ×400.

Fig. 17. Ovary. ×400.

Fig. 18. Plain muscle. ×400.

Fig. 19. Epithelium of diverticulum. ×400.

Fig. 20. Connective tissue of proboscis. ×400.

Fig. 21. Muscle bands in proboscis connective tissue. ×400.

[Pg 31]

[Pg 32]

[Pg 33]

[Pg 34]

Opisthobranchs from Laguna Beach

The determinations are by Dr. F. M. MacFarland

TECTIBRANCHS

NUDIBRANCHS

[Pg 35]

Central Nervous System of the Sand

Dollar Dendraster Excentricus Esh

WILLIAM A. HILTON

There seems to be little or no literature on the central nervous system of this
form of echinoderm. As might be expected, the general arrangement of radial and
circumoral bands are much as in sea-urchins, such as shown especially by Delage and
Herouard 1903. There are however some interesting features which make the study
of this type of special value.

In this paper only the chief mass of the central nervous system is considered. The
more evident parts of the central nervous system are arranged in general as in other
forms. The circumoral nerves issue from under the lantern and run along the oral,
cross over at the edge of the shell and then run along the aboral side. The five radial
nerves converge at the five ocular areas near the center of the aboral region. The
circumoral nerve ring is looped over and under parts of the lantern. Fig. 1 shows
a part of the lantern and parts of three loops of the circumoral nerve trunk. In the
center of the figure one fifth of the lantern is drawn in and from under it a radial
nerve is shown in the lower part of the figure. To the left and to the right of the
central bony part of the lantern the union of a radial with a circumoral nerve is
shown. At the junction of each radial nerve with the circumoral, is a little thickening
which seems to be a special cellular mass such as I have not found in other forms.
Fig. 7 is a section through a part of a circumoral strand, much enlarged. There are
only a few nerve cells, from one to two layers.

As the radial nerves leave the lantern they are quite evident in dissected specimens
as they are close to the bony skeleton with very little connective or other tissues
to obscure them. The use of aqueous methylene blue aids in following the smaller
branches. Near the lantern the branches are small as shown in fig. 2. When the
region is reached where the upper and lower surfaces of the shell begin to fuse, the
branches become larger and more irregularly arranged, as shown in the lower part
of fig. 1 and fig. 2.
After the nerve turns to run on the aboral side there is no change
in arrangement until the region of the tube feet is reached. In the region of the tube
feet the nerves become more numerous, smaller and more regular. The general distribution
of the nerves and the arrangement of the tube feet nerves are shown in fig. 4
which is from part of the upper end of the aboral nerve. The holes in the skeleton
for the tube feet are shown as circles on each side of the diagram.

The general structure of the chief central nerve trunks is quite similar as shown
in sections. Figs. 6, 7 and 8.
The nerve trunks have about one to two layers of
cells, the main part of the nerves are composed of longitudinal fibers. There are not
so many evident vertical fibers from cells as found in starfish and some other forms.
This change in position of the fibers may be in part due to the general modification
of structure. Whether this arrangement leads to other types of nerve association is
a question.

When the nerve trunks are removed, stained in methylene blue and examined
with the microscope something of the arrangement of the cells may be seen. In the
circumoral and oral radial nerves the nerve cells are thickly massed from side to side,
but in the upper part of the aboral nerve there is an evident arrangement of nerve
[Pg 36]
cells in zones. There is usually a central more or less clear zone, next on each side
a rather dense cell area and next on each side a very dense cell area, then a narrow
nearly clear zone on each side again.

As a rule slightly larger cells are found near the nerve trunks and as some of
these seem to send long branches out into the lateral trunks, they may be motor or
sensory, the association neurones are probably the smaller cells in farther. The cells
seem multipolar in most cases and in fact much more modified than the cells of starfish
or sea-urchin. Figs. 9 and 10.

REFERENCES

(Contribution from the Zoological Laboratory of Pomona College)

Explanation of Figures

Fig. 1. Diagram of one fifth of Aristotle's lantern of Dendraster showing three
loops of the circumoral nerve ring, and parts of three radial nerves, the central one
partly hidden at its origin by the lantern. The nerves are in black. ×9.

Fig. 2. Drawing of part of the first part of an oral radial nerve. ×9.

Fig. 3. Drawing of the lower end of an oral radial nerve. ×9.

Fig. 4. Drawing of the upper part of an aboral radial nerve. The eye spot
region is up in the figure. ×9.

Fig. 5. Camera lucida drawing of a part of an aboral nerve showing position of
cell areas. ×70.

Fig. 6. Drawing of a section of an oral radial nerve. ×300.

Fig. 7. Drawing of a section of circumoral nerve. ×300.

Fig. 8. Drawing of a section of aboral nerve. ×300.

Fig. 9. Nerve cells from central regions of a radial nerve. The arrangement
is as shown in the drawing, cells of various levels shown as one layer. Some of the
processes possibly relate nearby cells, but most fibers run into the general fibrous mass.
All fibers or fibrils are small. There is some indication of tigroid substance in some
of the cells. ×450.

Fig. 10. Nerve cells from near a lateral branch from the radial band. ×450.

[Pg 37]

[Pg 38]

Ants from the Claremont Laguna Region

This list includes ants collected chiefly in 1917. All determinations are by Dr. W. M.
Wheeler.

(Contribution from the Zoological Laboratory of Pomona College)

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