Studies of the Development and Larval Forms of Echinoderms

Abstract

THE development of Echinoderms from the egg presents one of the most striking of life processes known to us. The changes through which the individual passes are even more remarkable than those accompanying the more familiar metamorphosis of a caterpillar into a butterfly. The egg develops directly into a free-swimming larva of bilateral structure, adapted in most cases for pelagic life; within this larva there is gradually formed a body with radial structure and special organs, which, being set free from the larva, grows into the adult sea-urchin, starfish, crinoid, or holothurian—an adult rarely free-floating and generally abiding in one place. It is almost as though there were an alternation of generations, as though the larva bore the young echinoderm as a mother bears a child; and this idea, though not really justified, is forcibly recalled by Dr. Mortensen's account of an ophiurid larva, which, after dropping the young brittle-star, proceeds to reconstitute its own body, and continues life as an independent individual. Dr. Mortensen even suggests, rather audaciously, that it may repeat the metamorphosis.

Studies of the Development and Larval Forms of Echinoderms.

By Dr. Th. Mortensen. Pp. iv + 261 + 33 plates. (Copenhagen: G. E. C. Gad, May, 1921.) 2l. 2s.