TROPIOMETUA CAllINATA. 3 



complete conformity with what has been made known by Seeliger in Antedon 

 adriaiica. 



The relative scarcity of the material, together with the not very good 

 preservation and the difficulty of the orientation of the embryos in the 

 younger stages, has prevented making a complete study of every detail in 

 the developmental process. Also the very rapid succession of the different 

 stages in the development has added considerably to the difficulties in secur- 

 ing every stage. Accordingly, this report of the development of Tropiomelra 

 is not quite so complete as that given by Seeliger in his elaborate memoir on 

 Antedon adriaiica. The previous literature on the embryological development 

 of Crinoids has been so thoroughly revised and criticized by Seeliger that we 

 need not here review it in detail, and subsequently there is only one memoir 

 to be taken into consideration, viz, the "Studii su gli Echinodermi," ' by 

 A. Russo. Literary discussions thus occupy only a small space of the embryo- 

 logical section of this work. This docs, however, not apply to the parts 

 relating to the post-embryonal development. 



In his paper " On the origin of certain types of Crinoid stems,"' A. H. Clark 

 suggests that Crinoids with a very wide distribution, like Tropiometra, must 

 have a prolonged free-swimming stage. "Are we justified in saying that 

 the larvae of Tropiometra may not turn out to be plutei or something 

 like them?" This interesting suggestion stimulated interest in the study 

 of the development of this species. The results, however, do not bear out 

 Clark's expectations. 



I expect that some day a Crinoid may be found with a truly pelagic 

 larva, resembling a Pluteus or Bipinnaria, but I think it more probable that 

 we may find it in some stalked Crinoid. In the Comatuhds I would expect 

 the case to be the same as in the Dendrochirote Holothurians, all having a 

 simple larva, provided with ciliated rings, but otherwise not specially adapted 

 to a pelagic life. The character of the egg bears a relation to this. In all 

 the numerous Dendrochirotes I have examined, the eggs are large and yolk- 

 laden, and I have no doubt that the larvae in these, and probably all other 

 Dendrochirotes, will prove to be of the usual simple Cucumarian type. In 

 all the Crinoids I have examined the eggs are likewise rather large and rich 

 in yolk, and I must infer from this fact that their larval form will also be of 

 the usual, simple type. A. H. Clark states that in the Thalassometridse the 

 eggs are small, and accordingly he expects them to have a long free-swimming 

 stage." It would be of considerable interest to study the development of 

 some species of this group. If the eggs in this family are really noticeably 

 smaller than in other Crinoids, and especially less supplied with yolk, we may 



• Atti dell'Accad., Gioenia, vol. xii, Mem. vii, 1902. 

 ' Proc. U. S. Nat. Mus., vol. 38, 1910, p. 213. 



• Vid. Medd., 1909, p. 122. 



