564 E. W. MACBEIDE. 



use of artificial fertilisatiou, and thus accuuiulated a certain 

 amount of information about the earliest stages of develop- 

 ment of Ophiurids other than Amphiura squamata. 

 Kowalevsky, in a paper devoted to Amphioxus (13), had even 

 before Metschnikoff's time noted the fact that the eggs of an 

 undetermined Ophiurid formed a gastrula by invagination. 

 Balfour had observed the same in the case of Ophiothrix 

 fragilis (3), Selenka in Ophioglypha lacertosa (31), 

 and Fewkes in Ophiopholis aculeata (9). These results 

 naturally led to increased scepticism as to the supposed 

 formation of the endoderm by delamination in Amphiura 

 squamata. In 1895 Bury published another paper entitled 

 "The Metamorphosis of Echinoderms" (6). This paper, 

 although containing most valuable observations on the other 

 groups of Echinoderms, as well as a general theory of the 

 phylogeny of the group, contains few new observations on 

 Ophiuroidea, the only notable one being a suggestion that 

 the left posterior cceloni encircles the stomach in the later 

 stages of development. This view Bury bases on a single 

 section, which showed a horizontal mesentery. 



Ziegler in 1896 published a short paper on the early stages 

 of development of Ophiothrix fragilis (33). His account 

 only reaches as far as the gastrulation, but he describes a 

 vacuolated crest which is very characteristic of these larvse. 



In 1900 Caswell Grave published an interesting and valuable 

 paper (12) on the development of Ophiura brevispina. 

 This species lays comparatively large eggs and has a shortened 

 development. It transpires, indeed, that the eggs develop 

 into the " worm-like " larva described by Johannes Miiller 

 and Krohn, which is thus shown to be the larva of Ophiura 

 brevispina, or of a closely allied species. Grave's material 

 was, as he himself explains, decidedly scanty, a circumstance 

 which renders it possible that some of his conclusions may 

 require revision should more abundant material become avail- 

 able. The first stage which he describes is an oval larva, li- 

 days old, uniformly ciliated and swimming freely. In this 

 stage an anterior, bilobed, coelomic vesicle is being constricted 



