404 F, M. BALFOUR. 



es^gs of Raja and Acantliias has been described by Gegenbaur.^ 

 lie finds it fiat in young eggs, but in the larger eggs of Acanthias 

 more columnar, and with the cells wedged in so as to form a 

 double layer. These observations are confirmed by Ludwig.^ 



Alexander Schultz^ states that in Torpedo, the eggs are at 

 first enclosed in a simple epithelium, but that in folhcles of 

 •008 mm. there appear between the original large cells of the 

 follicle (which he describes as granulosa cells and derives from 

 the germinal epithelium) a number of peculiar small cells. He 

 states that these are of the same nature as the general stroma 

 cells of the ovary, and believes that they originate in the stroma. 

 When the eggs have reached O'l — 0"15 mm., he finds that the 

 small and large cells have a very regular alternating arrange- 

 ment. 



Semper records but few observations on the follicular epithe- 

 lium, but describes in Eaja the presence of a certain number of 

 large cells amongst smaller cells. He believes that they may 

 develope into ova, and considers them identical with the larger 

 cells described by Schultz, whose interpretations he does not, 

 however, accept. 



My own results accord to a great extent with those of Dr. 

 Schultz, as far as the structure of the follicular epithelium is 

 concerned, but I am at one with Semper in rejecting Schultz's 

 interpretations. 



In Scyllium, as has already been mentioned, the follicular epi- 

 thelium is at first flat and formed of a single layer of uniform 

 cells, each with a considerable amount of clear protoplasm and a 

 granular nucleus. It is bounded externally by a delicate mem- 

 brane — the membrana propria folliculi of Waldeyer — and inter- 

 nally by the vitelline membrane. In the ovaries of very young 

 animals the cells of the folHcular epithelium are more columnar 

 on the side towards the stroma than on the opposite side, but this 

 irregularity soon ceases to exist. 



In many cases the nuclei of the cells of the follicular epithe- 

 lium exhibit a spindle modification, which shows that the growth 

 of the follicular epithelium takes place by the division of its 

 cells. No changes of importance are observable in the follicular 

 epithelium till the egg has reached a diameter of more than 

 1 mm. 



It should here be stated that I have some doubts respecting 

 the completeness of the history of the oj)itliclium recorded in 

 the sequel. DiificuUies have been met witii in completely eluci- 

 dating the chronological order of the occurrences, and it is pos- 

 sible that some points have escaped my observation. 



1 Loc. cit. ^ Loc. cit. ' Loc. cit. 



