Papers from the Department of Marine Biology of the Carnegie Institution of Washington Vol xvi Studies in the Development of Crinoids

Abstract

THE early stages in the life-history of recent crinoids have always been regarded with interest, because it was hoped that they would throw light on the evolution of this class, so rich and various in ancient seas, and on its relation to the other very differently fashioned classes of Echinoderma. Unfortunately, the only forms that have up till now furnished material for the em-bryologist are the unstalked comatulids, or feather-stars, and in the past such material has come from but a single genus, and from only three closely allied species of it—Antedon bifida of our own coasts, A. mediterranea, and A. adriatica. The accounts of their development by W. B. Carpenter, Bury, Seeliger, and others have shown slight differences, due, in part, probably to specific distinctness of the material. Even if it were not feasible to obtain the early stages of any stalked crinoid, still a study of other species, representing other genera of comatulids, was much to be desired, since it might then be possible to infer which features were peculiar to Antedon and which were common to comatulids generally, if not to the whole class Crinoidea. Such a study has now been made by Dr. Morten-sen, who has obtained a fairly complete series in four genera, and the pentacrinoid larvae of two others. His results are set forth in clear English with his usual care, and the memoir is illustrated by admirable drawings from his own pencil. His many interesting results are discussed in a “General Part” which demands the attention of professed morphologists. Here we shall select for comment a few observations that bear on the past history of the class. Papers from the Department of Marine Biology of the Carnegie Institution of Washington. Vol. xvi. Studies in the Development of Crinoids. By Th. Mortensen. (Publication No. 294.) Pp. v + 94+xxviii plates. (Washington: The Carnegie Institution of Washington, 1920.) 6 dollars, post free.