OVARIES IN TELEOSTEAN AND ELASMOBRANCH FISHES. 173 



" germinal epithelium/^ — that is to say^an epithelium covering 

 or (Teleostei) lining the ovary, and possessing the theoretically 

 unlimited power of giving rise to new oogonia by the trans- 

 formation of certain of its cells in a way described by Balfour 

 (1878) and many others. Jungersen, then, considers that 

 ova are never formed de novo from the epithelial cells, 

 neither does he derive the follicular epithelium from this 

 layer, but from the stroma. An identical opinion is expressed 

 by Eigenmann, who says, " There is no doubt concerning 

 the continuity of the reproductive cells in Cy matogaster ; 

 they may be followed from very early conditions till sexual 

 maturity without once losing their identity. No somatic cells 

 are ever transformed into reproductive cells, and the com- 

 parative constancy of the latter up to 7 mm. makes it probable 

 that none are ever changed into any other structures." 



The earlier accounts of the ova and follicular epithelium in 

 Teleosteans differ, in some respects, from my own observations. 

 Thus Brock (1881) thinks that the nests of primitive ova in 

 Perca are formed by an immigration into the stroma of 

 epithelial cells. He found in a nest all transitions from 

 epithelial cells to the smallest primitive ova. Kollessuikov 

 (1878) had previously described and figured for Perca an 

 actual invagination of epithelium to form a " nest " after the 

 manner of formation of a Pfliiger's tube in the mammalian 

 ovary. In figs. 4 and 5 of the present paper a similar 

 appearance is presented. Emery (1880) states that in 

 Fierasf er the ovum originates from the germinal epithelium, 

 and he figures a row of cells in the epithelium showing transi- 

 tion stages from ordinary epithelial cells to oogonia. He 

 does not describe the formation of nests, nor is he able to say 

 much as to the origin of the follicular epithelium. Stuhlnianu 

 (1887) says that in Zoarces the ova are formed from certain 

 cells of the ovarian epithelium which sink into the stroma 

 accompanied by neighbouring cells, and that the latter give 

 rise to the follicular epithelium. Stuhlmann does not appear 

 to have noticed particularly the formation of nests. 



The evidence on this head at present available would seem to 



