27 



In this stage the larvse remained for some days without apparent changes, 

 when by an accident the whole culture was destroyed. In vain I attempted 

 to get ripe specimens 

 for making a new cul- 

 ture. More than a hun- 

 dred specimens were 

 opened, but all of 

 them were perfectly 

 empty. There was thus 

 no possibility of get- 

 ting the later develop- 

 mental stages, which 

 would have been of 

 very considerable in- 

 terest, nobody having 

 as yet studied the 



fully formed larva or Fig. 2. Skeleton of the larva of Diadema antillarum; side view. 

 the metamorphosis of ^' showing the whole basket structure, =»%; B. half part of the 

 ^. , ,., skeleton. =90/^. Letters as in fig. 1. 



any Diadematid — 



excepting the larva described by Joh. Miiller (VII. Abh. p. 9, Taf. V. 

 1 — 4), which is probably, but not beyond doubt, the larva of Centroste- 

 phanus longispinus. 



Astropyga pulvinata (Lamck.). 



PI. v. Figs. 6 and 7 (?). 



At the beginning of December 1915 I succeeded in finding (at Taboga, 

 Panama) some specimens of this fine Diadematid containing ripe genital 

 products. Fertilization was undertaken and a very good culture obtained. 

 The larvae developed quite normally till the first Pluteus-stage was reached, 

 but then they became unhealthy and died at the age of 6 — 7 days. An- 

 other culture made some days later went on exactly in the same way. 

 Thus also of this Diadematid only the first stage was obtained. As might 

 be expected, it is in the main features similar to that of Diadema. 



The eggs are small (exact measurements were not made) and transpar- 

 ent. The cleavage is of the usual regular modus, presenting no especially 

 noteworthy features; the process of gastrulation may perhaps prove 

 unusual, but on account of absence on a dredging trip I could not follow 

 it satisfactorily so I shall not enter on the subject. At the age of ca. 24 

 hours the embryos had begun to assume the Pluteus-shape. They are at 

 this stage rotating at a great speed, always to the right i), so fast, indeed, 



1) In my paper "On the development of some British Echinoderms" (Journ. Mar. Biol. 

 Assoc. X. 1913. p. 6) I have stated that the young embryos of Asterias glacialis and other 



4* 



