214 THE DEVELOPMENT OF ELASMOBRANCH FISHES. 



"A specimen of this kind is represented in Plate 14, fig. 2, n. y, where 

 the meshes of the network are seen to be finer immediately around the 

 nuclei, and coarser in the intervals. The specimen further shews, in the 

 clearest manner, that this network is not divided into areas, each represent- 

 ing a cell and each containing a nucleus. I do not know to what extent this 

 network extends into the yolk. I have never yet seen the limits of it, though 

 it is very common to see the coarsest yolk-granules lying in its meshes. 

 Some of these are shewn in Plate 14, fig. 2,_y. k." [This edition, p. 65.] 



Dr Schultz, by employing special methods of hardening and 

 cutting sections of the whole egg, has been able to shew that 

 this network extends, in the form of fine radial lines, from the 

 centre to the circumference ; and he rightly states, that it exhibits 

 no cell-like structures. I have detected this network extending 

 throughout the whole yolk in young eggs, but have failed to see 

 it with the distinctness which Dr Schultz attributes to it in the 

 ripe ovum. Since it is my intention to enter fully both into the 

 structure and meaning of this network in my account of a later 

 stage, I say no more about it here. 



At one pole of the ripe ovum a slight examination demon- 

 strates the presence of a small circular spot, sharply distinguished 

 from the remainder of the yolk by its lighter colour. Around 

 this spot is an area which is also of a lighter colour than the 

 yolk, and the outer border of which gradually shades into the 

 normal tint of the yolk. If a section be made through this part 

 (vide PI. 6, fig. i) the circular spot will be found to be the 

 germinal vesicle, and the area around it a disc of yolk containing 

 smaller spherules than the surrounding parts. The germinal 

 vesicle possessed the same structure in both the ripe eggs 

 examined by me ; and, in both, it was situated quite on the 

 external surface of the yolk. 



In one of my specimens it was flat above, but convex below ; 

 in the other and, on the whole, the better preserved of the two, 

 it had the somewhat quadrangular but rather irregular section 

 represented in PI. 6, fig. I. It consisted of a thickish membrane 

 and its primitive contents. The membrane surrounded the 

 upper part of the contents and exhibited numerous folds and 

 creases (vide fig. i). As it extended downwards it became 

 thinner, and completely disappeared at some little distance from 

 the lower end of the contents. These, therefore, rested below on 

 the yolk. At its circumference the membrane of the disc was 



