INTKA-OVARIAN EGG OF SOME OSSEOUS FISHES. 69 



His, Waldeyer, Brock, and others, deny the existence of an 

 inner membrane. 



In theory, the presence of such a membrane would explain 

 much which seems at present very difficult. If it really existed, 

 we would naturally regard the zona as being secreted from it. 

 It would also place the pores of the former into the same 

 category as those occurring in cuticular formations, with which 

 they indeed have much resemblance. 



IV. The Follicular Layer. 



The follicular layer, or granulosa, surrounds the egg-mem- 

 branes which I have just mentioned. In the next paragraph 

 I shall speak about its development ; hence I need only 

 describe its appearance in the ripe intra-ovarian egg. 



In the gurnard's egg it consists of a layer of closely-set 

 cells, which has an average thickness of O006 mm. Seen from 

 above, the cells present hexagonal outlines with a central 

 nucleus (fig. 16). The egg lies in a stroma of connective 

 tissue. 



In the shanny's egg (Blennius pholis) the follicle is 

 peculiarly modified (fig. 15,/.). The depth of the cells, which 

 in one half of the egg is only about 0*007 mm., gradually 

 increases until it reaches 0032 mm. at the opposite side. The 

 cells at that side become drawn out and taper towards the 

 surface of the egg. The space between the cells is filled up 

 with interstitial substance (i. s.). Another feature about the 

 follicle in this case is that it touches the zona in all parts, 

 except in a circular portion (c.p.), where it is not in immediate 

 contact with it. This space is filled with an apparently viscid 

 substance, which no doubt is secreted by the follicular cells. 



Similar peculiar modifications of the granulosa have been 

 observed by Eimer and Brock. McLeod 1 likewise mentions 

 a granulosa composed of elongated cells as occurring in 

 Gobius niger. 



1 McLeod, " Recherches sur la structure et le developpement de l'app. 

 reproduct. femelle des Teleosteens," 'Arch, de Biologie,' vol. ii, 1881. 



