INTRA-OVARIAN EGG OF SOME OSSEOUS FISHES. 65 



" zonoid layer." It stains only slightly, and I have found it 

 as a rule devoid of granules or vesicles. In the ripe ova this 

 zonoid layer disappears entirely. I cannot agree with His, 

 according to whom it is replaced by the egg-capsule or zona, 

 as the latter is always formed before the zonoid layer. 



Brock 1 thinks that this thick layer is a peculiarity, probably 

 in some relation to the nourishment and growth of the egg. 



According to Kupffer, 2 the membrane surrounding the yolk 

 in the herring's egg consists of two layers, viz. an inner finely 

 striated and an outer one into which the strise are not continued. 

 The striae, he says, might be radial pores, however, he must 

 point out that, as the pores are not found in the external layer, 

 they certainly do not open exteriorly. Eimer 3 first noticed the 

 stripes in the zonoid layer, which he believes are due to pro- 

 cesses from the follicle. He saw the stripes in Alburnis 

 lucidus, Salmo fario, and Perca fluviatilis, but they 

 only occupied the outer half and are not so delicate as those 

 in the zona. That this layer belongs to the yolk, he says, 

 is seen by the fact that in separating it follows always the 

 latter. My own observations are in direct opposition to this 

 last statement. Eimer also speaks of a membrane externally 

 to the zona. He believes that it originates from the follicular 

 layer and therefore might be looked upon as a chorion. 



The same author regards the radial striation in the zona 

 radiata as being due to little rods between which are found 

 pores. He likewise examined the ovum of Reptiles, in which 

 he noticed besides the zona and the external ff chorion," an 

 internal membrane, of which I shall have to speak presently. 



Kolliker 4 says " there is in all fishes' eggs an outer, more 

 resistant, thinner layer externally to the zona which may even 

 preserve the striation in some cases. 



1 Brock, " Beitrage z. Anatoniie und Histologie d. Geschlechtsorgane d. 

 Knoclienfishe," ' Morphol. Jahrbucb,' vol. iv, 1878. 



2 Kupffer, 'Die Entwicklung d. Herings im Ei,' Berlin, 1878. 



3 Eimer, " Untersucbuugeu iiber d. Ei d. Reptilien und Fiscbe," ' Arcbiv f. 

 Mikr. Anatomie,' vol. viii, 1872. 



4 Kolliker, "Untersucbuugeu z. vergleicbenden Gewebelehre (also on 

 Ovum)," ' Verhandl. d. Pbys. Medic. Gesellscbaft,' Wurzburg,' vol. viii, ] 858. 



VOL. XXVIII, PART 1, NEW SER. E 



