2 STUDIES IN THE DEVELOPMENT OF CRINOIDS. 



Thus the present memoir contains the description of the complete, or 

 nearly complete, development of three new types of Crinoids and of part 

 of the development of three other types. 



My sincerest thanks are tendered to Dr. A. G. Mayor for the oppor- 

 tunity to take part in the expedition to Tobago, thereby affording me such 

 exceptional advantages for extending my studies in the embryology 

 of Echinoderms. 



A short preliminary report on the results obtained in the embryology of 

 Echinoderms during my stay at Tobago was published in the Year Book of 

 the Carnegie Institution of Washington for 1916. The final report on the 

 Echinoderms not included in the present memoir will be incorporated in 

 the report on my researches on Echinoderm larvae, carried on during my 

 Pacific expedition. 



I. TROPIOMETRA CARINATA (Lamarck) .» 



(Plates I to X.) 



This Crinoid occurs in fair numbers in places on the coral reef at the 

 western end of the island of Tobago, British West Indies, sometimes in such 

 shallow water that it is exposed at lowest tide. It is a very hardy species, 

 and there was no difficulty in keeping specimens alive in jars, even for several 

 days. Late March and April were just in the breeding-season, and the first 

 lot of specimens gave a few larvae. After this I succeeded repeatedly in 

 getting cultures of larvae, never in great numbers, but sufficient to enable 

 me to secure material for a fairly complete study of its development. 



As the red-brown larvae are quite opaque, nothing of the interior structure 

 and its successive transformation could be seen on the living object. Only 

 the first cleavage stages could be studied directly; but from the gastrula 

 stage onwards the whole developmental process, excepting the development 

 of the skeleton, must be studied by means of sections. Not being prepared 

 for preserving material for sections, I had no other preserving fluids than 

 corrosive sublimate and alcohol. The sublimate did not give very good 

 results; the material preserved in alcohol was decidedly better. But upon 

 the whole the preservation is not good enough for studying histological 

 details. Thus, for instance, the larval nervous system could not be studied 

 satisfactorily. However, here and there histological details could be seen 

 which tended to show that as regards the histological development there is 



' The specific name carinata adopted here is used on the authority of H. L. Clark, who mentions 

 the species under this name in his report on the Echinoderms of Tobago. A. H. Clark, who formerly (On a 

 collection of Crinoids from the Museum of Copenhagen, Vid. Medd. N. Foren. 1909, p. 182) held the same 

 view, now (in The recent Crinoids of the coasts of Africa, Proc. U. S. Nat. Mus., 40, 1911) regards 

 the Atl.intic species of Tropiometra as specifically distinct from the Tropiomelra carinata of the Indian 

 Ocean, the Atlantic species being designated as T. picta (Gay) {brasiliensis Liitken). From a zoogeographic 

 point of view I would expect them to be different species, but for want of sufficient material of the Indian 

 form I have no opportunity for forming my own judgment in this case. Accordingly I have thought it 

 my duty here to follow H. L. Clark in using the name carinata for the Atlantic form. 



