OVARIES IN TELEOSTRAN AND ELASMOBRANCH FISHES. 171 



Wlien we do find oogonia in the stroma they are ag'gregated 

 into roundish balls, " nests " of karyokinetically dividing 

 cells (figs. 1 — 5, 14, 15) J in direct connection with the 

 epithelium. From their compact rounded form the balls of 

 oogonia have evidently been produced by the repeated 

 division of a single mother cell. Further, the mother cell 

 must have been situated in or just under the epithelium. 

 One may, in fact, find all stages, from a single oogonium 

 dividing into two whilst in the epithelium, to subepithelial 

 collections of such, the "nests " just mentioned. 



Closely wedged in amongst the oogonia of snch a nest 

 (fig. 1) are a number of small deeply staining nuclei. Some 

 of these will form the follicular epithelium of subsequently 

 developed oocytes (figs. 2, o). The origin of these interstitial 

 cells is somewhat difficult to make out. The nuclei of these 

 cells are, on the whole, more like those of the ovarian epi- 

 thelium than like the nuclei which occur in the stroma. 

 Their chromatin, for one thing, is more pronounced. Figs. 

 4, 5, which represent portions of a section of a maturing 

 ovary (February), show two '^ nests " formed entirely of 

 follicular epithelial cells. The conditions here are very sug- 

 gestive of an inward proliferation of cells of the ovarian 

 epithelium. The absence of oogonia or oocytes in these 

 particular "nests" may be accounted for by assuming either 

 that the ova which were originally present have degenerated, 

 or that none were formed, the proliferation inwards of the 

 ovarian epithelium not being associated, as normally, with a 

 transformation of certain elements into oogonia. 



As to whether a fusion of oogonia normally occurs in connec- 

 tion with the formation of a permanent ovum or oocyte, I am 

 inclined to think that this does take place, but that it does 

 not involve the whole contents of a nest. The oogonia of a 

 nest do not all fuse together to form a syncytium in which the 

 nuclei multiply without corresponding division of the proto- 

 plasm, and from which a permanent ovum is subsequently 

 separated in the manner described by Semper (1875) and 

 Balfour (1878) in Elasmobranchs. Fig. 2 represents two 



