198 STILIFERIDjE. 



with about 40 clusters of spawn, in various stages of de- 

 velopment, evidently belonging to the pair of Stilifers 

 above mentioned. The fecundity of this species must be 

 very great ; and the shell therefore ought not to be rare. 

 I counted at least 100 fry in one of the clusters of spawn ; 

 so that one sea-egg would yield in a single year a pro- 

 spective harvest of 4000 specimens enough to supply 

 almost all the conchologists in the world, unless some of 

 them were more greedy than usual. Moreover one of 

 the adult Stilifers appeared to be full of spawn, which 

 was perceptible through the transparent shell. Since an 

 Echinus could barely accommodate half a dozen indivi- 

 duals when they arrived at maturity, what would have 

 become of the rest, supposing they escaped being the prey 

 of other animals ? Would they have migrated, and 

 formed colonies on other sea-eggs? The Stilifer possesses 

 both a foot and eyes ; and appropriate quarters are by 

 no means wanting in the same part of the sea-bed whence 

 I procured the specimens which have given rise to the 

 above remarks. The spawn-masses are oval, each en- 

 veloped in a gelatinous case. When detached, and ex- 

 amined under a microscope, the fry was seen to have 

 three lobes, the larger two of which were in front ; the 

 lobes were finely ciliated, the cilia being rather long, 

 and their points sometimes touching the surface of a 

 small glass tube which contained the detached fry. 

 These rapidly whirled about by the aid of their cilia, 

 on which they now and then rested. They occupied 

 nautiloid shells of a single whorl, into which (unlike the 

 adult) they were capable of entirely withdrawing. The 

 embryogeny of Stilifer has also been noticed by Dr. 

 Otto Semper in Siebold and Kolliker's ' Zeitschrift firr 

 wissenschaftliche Zoologie' for 1864, and placed by 

 him in the same category with that of Eulima and So- 



