DEVELOPMENT OF ELASMOBRANCH FISHES. 3 



of the membrane filled by the contents ; and the upper part of 

 the membrane is so folded and creased that sections through 

 almost any portion of it pass through the folds. The regularity 

 of the surface of the yolk is not broken by the germinal 

 vesicle, and the yolk around exhibits not the slightest signs of 

 displacement. In the germinal vesicle figured the contents 

 are somewhat irregular in shape ; but in my other specimen 

 they form a regular mass concave above and convex below. In 

 both cases they rest on the yolk, and the floor of the yolk is 

 exactly moulded to suit the surface of the contents of the 

 germinal vesicle. The contents have a granular aspect, but 

 differ in constitution from the surrounding yolk. Each germi- 

 nal vesicle measured about one-fiftieth of an inch in diameter. 



It does not appear to me possible to suppose that the pecu- 

 liar, appearances which I have drawm and described are to be 

 looked upon as artificial products either of the chromic acid, in 

 which the ova were hardened, or of the instrument with which 

 sections of them were made. It is hardly conceivable that 

 chromic acid could cause a rupture of the membrane and the 

 ejection of the contents of the vesicle. At the same time the 

 uniformity of the appearances in the different sections, the regu- 

 larity of the whole outline of the egg, and the absence of any 

 signs of disturbance in the yolk, render it impossible to believe 

 that the structures described are due to faults of manipulation 

 during or before the cutting of the sections. 



We can only therefore conclude that they represent the 

 real state of the germinal vesicle at this period. No doubt 

 they alone do not supply a sufficient basis for any firm con- 

 clusions as to the fate of the germinal vesicle. Still, if they 

 cannot sustain, they unquestionably support certain views. The 

 natural interpretation of them is that the membrane of the 

 germinal vesicle is in the act of commencing to atrophy, pre- 

 paratory to being extruded from the egg, while the contents of 

 the germinal vesicle are about to be absorbed. 



In favour of the extmsion of the membrane rather than its 

 absorption are the following features, 



(1) The thickness of its upper surface. (2) The extension 

 of its edge over the yolk. (3) Its position external to the yolk. 



In favour of the view that the contents will be left behind 



1—2 



