These brittle stars are common in Lagoon Pond on Martha's Vineyard, Mass., where they are dredged from sandy bottoms among living and dead grasses and algae. The sexes are separate, and are similar in appearance.

Grave ( 1916) states that the breeding season at Beaufort, N. C., is in June and July. At Woods Hole, Mass., observations indicate that spawning occurs during July and at least the first part of August.

A. Care of Adults: The animals should be kept in aquaria provided with a constant supply of sea water. They do not need to be fed, and will remain in good breeding condition for a considerable period of time. Fertile eggs, which developed normally through metamorphosis, have been obtained from Ophioderma after a month in a laboratory aquarium. During this period the same animals had previously produced several batches of eggs.

B. Procuring Gametes: Artificial insemination has not proved successful in this species, but naturally-shed eggs may be readily obtained during the evening, provided that the animals are in breeding condition. Grave (1916) states that the males begin to spawn about 8 P.M., and it has since been observed that this process of spawning may continue until midnight.

The animals should be removed at sunset from the aquarium to a fingerbowl containing sea water, placed near a window. The males will begin to shed sperm; the presence of sperm in the water seems to induce the females to release their eggs. When the sperm concentration is very dense, a great number of immature eggs are shed along with the mature ones (Grave, 1916).

C. Preparation of Cultures: It is important to transfer the eggs to fingerbowls of fresh sea water as soon as possible after shedding, as the dense sperm suspension tends to induce abnormal development. Since the eggs are relatively large, the transfer is easily accomplished with the aid of a pipette. Both eggs and young larvae should be removed to fresh sea water at least twice a day. The cultures should be covered and kept on a water table.

NORMAL DEVELOPMENT :

A. The Unfertilized Ovum: The egg is pelagic and floats to the surface as soon as it is released. It is very opaque, due to the presence of yolk. The color may vary from yellow to dark green, but within a single batch of eggs it is uniform. The average diameter of this egg is approximately 300 microns (Grave, 1916). The egg is probably shed after the formation of the polar bodies.

B. Fertilization and Cleavage: The eggs are fertilized as they are shed into the water. Cleavage is total and equal, closely resembling that of Asterias. A thickwalled hollow blastula is formed. Gastrulation is by invagination.

C. Rate of Development: At a laboratory temperature of 24• C., the early cleavages occur at half-hour intervals. A rotating blastula is formed in 10 to 12 hours, and a gastrula 18 to 20 hours after fertilization. At 48 hours, the rudiments of the arms are visible. At 96 hours, the first tube feet appear as small protuberances, and at 120 hours, some of the larvae are able to crawl along the bottom.

D. Later Stages of Development: The young, yolky, larvae are cone-shaped with a flattened blastoporic pole at the time of gastrulation. They are completely covered with cilia which enable them to move slowly through the water. As they gradually elongate, the blastopore is displaced ventrally and the stomodeal depression becomes visible. Two lateral thickenings next appear, just below the equator of the embryo. The blastopore now closes, and the cilia become concentrated in the form of four bands. Five groups of elevations soon appear about the stomodeum, on the ventral surface of the flattened oral disc. Each group consists of three elevations, the rudiments of the end tentacle and the first two tube feet of each arm. In the course of further development the arms elongate, additional tube feet are added, the ciliated bands are raised on ridges, and the old "anterior" pole of the larva degenerates. For diagrams of the larvae and for a description of the internal development, see the paper by Brooks and Grave (1899).

BROOKS, W. K., AND C. GRAVE, 1899. Ophiura brevispina. Mem. Nat. Acad. Sci., 8: 79 - 100. Also in Mem. Biol. Lab., Johns Hopkins Univ., 4: no. 5, pp. 79-100.

GRAVE, C., 1916. Ophiura brevispina. II. An embryological contribution and a study of the effect of yolk substance upon development and developmental processes. J. Morph., 27: 413-451