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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 lo recall I he convolutions of a brain. Sections through 

 embryos of this stage show I hat this is due lo a strong folding of the 

 blastula (PI. V Fig. 1), much as il occurs in Aslropeclen 1 ), Luidia-), Sol- 

 uxler 3 ), 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. 13 u I 

 there is no reason lo enter on a discussion thereof on this occasion. - 

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



At the age of 28 hours they were found lo be swimming gaslrula?, 

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

 Fig. 1 represents a section through one of these gaslruhe; il is very 

 Ihiekwalled, I lie nuclei lying in a thick layer. The invagination appears 

 bipartite, which will probably mean thai Ihe formation of the coelomic 

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

 cells. It appears thai the invagination is set with long cilia - but Ihe 

 preservation is nol sufficiently good for ascertaining Ihis definitely. 



None of Ihe embryos got beyond Ihis stage, and il was impossible to 

 get a new culture. But Ihe 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 antillarum Phil. 



I'l.V Fig. :.. 



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

 at Hawaii and Panama 5 ) I was very pleased in finding, at the end of March 

 1916, al Tobago 1>. \V. 1. ripe specimens of Diadema anlillarnm, from 

 which an excellenl culture of larva? was obtained. 



M E. Metschnikoff. Vergleichend embryologische Studien. Xcitschr. I. \viss. Zool. 

 Hd. XLII. 188.">. p. 660. 



'-) Th. Mortcnsc-ii. On the development of some British Ei-liinoilernis. Journ. M;ir. 

 Biol. Assoc. L". Kingdom. X. I'.H.'i. p. 7. 



3 ) J. F. Genimill. The development of the starfish Solaster endeca. Trans. Zoo!. Soc. 

 London. XX. 1912. 



4 ) A. T. Masterman. The early development of Cribrclla oculata ( Forbes i with remarks 

 on Echinoderm development. Trans. R. Soc. Edinburgh. XL. I'lnj. 



6 ) A few small specimens of Diadema mc.rirainuu were found to contain ripe sexual pro- 

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

 twice, but the embryos did nol develop beyond the gastrula stage. 



4 



