382 EYCLESHYMER. [Vol. X. 



ferentiated, the dorsal groove is deep and wide, there is no 

 indication of optic vesicles, and the embryo is obviously in a 

 much earlier stage of development — a fact of no little theoreti- 

 cal interest as an illustration of the relation existing between 

 embryo and yolk. If these forms be compared with Coregonus 

 (Fig. 16), the effect is more pronounced, the blastopore being 

 almost closed before the outlines of the embryo are distinct, 

 recalling the condition observed in Petromyzon and Amphibia. 



Fig. 21 represents a later stage of Lophius. The germ-ring 

 shown in Fig. 20 constricts and is represented by the two por- 

 tions surrounding the vesicles c.v. and c.vJ In some cases 

 the anterior ring is united on either side with the provisional 

 hind-end of the embryo. In others the tail apparently lies free, 

 the ring joining the embryo at a point considerably anterior. 



Fig. 13, PI. XXI, represents a median saggital section 

 through an embryo at the stage just described. The provis- 

 ional hind-end is well defined ; the real hind-end being now at 

 g.r.f and consisting of a mass of cells easily distinguished from 

 the surrounding periblast {per). The anterior ring is continuous 

 with the provisional hind-end and the area enclosed by it is 

 filled by a layer of periblast {per), forming the roof of the cav- 

 ity {c.v). The walls of this cavity are lined with periblast. 

 Lying immediately posterior to the vesicle (c.v) is another {c.v.'), 

 likewise lined with periblast. The layer of periblast form- 

 ing the lateral walls and roof of these vesicles is of consider- 

 able thickness, while the portion forming the floor is of such 

 extreme tenuity that it is often impossible to trace it through- 

 out its entire extent. The roof of the anterior vesicle {c.v) is 

 formed by a layer of periblast only ; over the posterior there is 

 usually an additional layer of epiblast {ep). I believe this 

 drawing over, or extension, of the epiblast to be a secondary 

 condition which offers no serious objection to considering the 

 posterior ring as representing a portion of the original germ- 

 ring. I have not been able to observe its formation in the 

 living embryo, consequently am unable to say more. 



Beneath the body of the embryo, at its posterior end, lies 

 the peculiar vesicle {K.v) to which Kupffer first called atten- 

 tion. 



