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

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.

Opisthobranchs from Laguna Beach

The determinations are by Dr. F. M. MacFarland

TECTIBRANCHS

NUDIBRANCHS

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