25 



cleavage was total and regular, in spite of the large size of the egg. The 

 next day the embryos had a very peculiar appearance, being folded in 

 such a way as to recall the convolutions of a brain. Sections through 

 embryos of this stage show that this is due to a strong folding of the 

 blastula (Pl.V Fig. 4), much as it occurs in Astropeden^), Lmdia% Sol- 

 aster^), Henricia*) and probably many other Asteroids, and as it is de- 

 scribed here also for Peronella Lesueuri. The cells are full of vacuoles, 

 which may probably be filled with some kind of nutritive fluid. But 

 there is no reason to enter on a discussion thereof on this occasion. — 

 Also in the following stage numerous vacuoles are seen, only much smaller. 



At the age of 28 hours they were found to be swimming gastrulae, 

 very slowly moving, quite opaque and with a very wide mouth. PI. V 

 Fig. 4 represents a section through one of these gastrulae; it is very 

 thickwalled, the nuclei lying in a thick layer. The invagination appears 

 bipartite, which will probably mean that the formation of the coelomic 

 pouch has begun. The blastocoel cavity is nearly filled by mesoderm 

 cells. It appears that the invagination is set with long ciUa — but the 

 preservation is not sufficiently good for ascertaining this definitely. 



None of the embryos got beyond this stage, and it was impossible to 

 get a new culture. But the facts here recorded are sufficient to show that 

 this species is very different as regards its development from the other 

 Cidarids thus far studied. Most probably its development will prove to 

 be direct, without a Pluteus-larva, or, in any case, the larva must be 

 greatly modified, on account of the character of the egg. The full record 

 of its development must be expected to be of quite unusual interest. 



Diadema antillarutn Phil. 



P1.V Fig. 5. 



After having sought in vain for ripe specimens of Diadema in both Japan, 

 at Hawaii and Panama^) I was very pleased in findingj at the end of March 

 1916, at Tobago B. W. I. ripe specimens of Diadema antillarum, from 

 which an excellent culture of larvse was obtained. 



1) E. Metschnikoff. Vergleichend embryologische Studien. Zeitschr. f. wiss. Zool. 

 Bd. XLII. 1885. p. 660. 



") Th. Mortensen. On the development of some British Echinoderms. Journ. Mar. 

 Biol. Assoc. U. Kingdom. X. 1913. p. 7. 



^) J. F. Gemmill. The development of the starfish Solaster endeca. Trans. Zool. Soc. 

 London. XX. 1912. 



*) A. T. Mas term an. The early development of Cribrella oculata (Forbes) with remarks 

 on Echinoderm development. Trans. R. Soc. Edinburgh. XL. 1902. 



') A few small specimens of Diadema mexicanum were found to contain ripe sexual pro- 

 ducts in January and February 1916 at Taboga, Panama. Fertilization was undertaken 

 twice, but the embryos did not develop beyond the gastrula stage. 



4 



