6 STUDIES IN THE DEVELOPMENT OF CRINOIDS. 



placed in the aquarium, under excellent conditions, suitable temperature, 

 and light. Although some of the Pentacrinoids were still alive, they did not 

 recover from the chilling and did not develop any farther, so that I thought 

 it useless to try to carry them alive with me to Copenhagen and preserved 

 them. I may mention here that I did succeed in carrying some young Echi- 

 nometra lucunter, which I had likewise reared from the egg in Tobago, alive 

 to Copenhagen. I beg to express here my sincerest thanks to Dr. Charles H. 

 Townsend, Director of the New York Aquarium, for his kind assistance. 

 There is no doubt that it would be possible to carry also young Pentacrinoids 

 alive and in good health to New York, if not exposed to too low a tempera- 

 ture, and in such case the New York Aquarium would be an excellent place 

 in which to keep the cultures for further study. 



Naturally there is no question of procuring food for the Crinoid larvae; 

 this trouble does not arise till the mouth has opened in the Pentacrinoid. 

 I used diatom cultures (Nitschia), procured in the way indicated by Allen 

 and Nelson, 8 and found this to be a very suitable food for the Pentacrinoids. 

 Also, by simply changing the water every day I found them growing nor- 

 mally. Some of the first Pentacrinoids reared I tried to plant out on the reef 

 in dishes, but without success, the dishes filling with sand, although placed 

 where there was very little surf. 



A difficulty in describing the development of a Crinoid arises from the 

 orientation, on account of the fact that the larva attaches itself with its 

 anterior end, the posterior end of the larva becoming thus the oral end of the 

 Pentacrinoid. Seeliger orients the Pentacrinoid in the same way as the larva, 

 head downwards. Although there is a morphological reason for this, it 

 seems to me too unnatural. Consequently I adopt the method of Bury, and 

 represent both the larva and the Pentacrinoid in their natural position. 9 



I. CLEAVAGE; FORMATION OF THE GASTRULA. FIRST 6 HOURS. 



The eggs (plate i, figure 1) are rather small, about 0.2 mm. in diameter, 

 opaque, whitish, with a faint reddish tint. On being discharged, they are 

 surrounded by a distinct, clear, follicular membrane. The peculiar structure 

 of the follicular membrane, described by Ludwig in Antedon mediterranea 

 (rosaceus) , 10 1 have not observed in Tropiometra. It is true I did not look 

 especially for it in the living object, not remembering anything about the 

 structure at that time (and I had, of course, no access to literature); but the 

 fact that I did not notice anything of the kind makes it fairly certain that 

 no such structure of the follicular membrane exists in this species. ll 



8 E. J. Allen and E. W. Nelson. On the artificial culture of marine plankton organisms. Quarterly 

 Journ. Micr. Sc., vol. 55, 1910. 



9 By a mistake figures 47, plate xxn, have been placed with the anterior end downwards. 



10 Die Dildung der Eihiille bei Antedon rosaceus, Zoolog. Anzeiger in, 1880, p. 470-471. 



11 Ludwig found the structure very distinct also in preserved condition; I have found no trace of such 

 structure in eggs taken from the pinnule of the preserved specimens of Tropiometra. 



