:24(3 Mr. E. A. Schafer. On Immature Ovarian Ovum [Mar. 18, 



these columns), as they successively mature, sink deeper into the 

 substance of the organ. 



It will be seen that the view which I have been led to take of 

 the derivation of the ova and epithelium cells of the Graafian follicles, 

 is that both structures originate in common from the germinal epi- 

 thelium — in the dog (Pfliiger, Waldeyer) in the form of ingrowths 

 which may closely simulate the formation of tubular glands (ovarial 

 glands) ; in the rabbit (Balfour) in the form of columns of cells 

 which are altogether solid, and which thus present a modifica- 

 tion of what is in all probability, as H. Ludwig's extensive comparative 

 researches have shown, the typical mode. This is essentially the view 

 first enunciated by Pfliiger ( 20 ) for the. vertebrate ovary, and differs 

 mnterially from that of Foulis, who contends for the derivation of the 

 follicular epithelium from the connective tissue cells of the ovarian 

 stroma. I think that Dr. Foulis couid not possibly have arrived at 

 this result had he at first selected the ovary of the dog for study. 

 Above all the investigation of the human ovary in this respect teems 

 with difficulties, both because it cannot be obtained fresh enough, and 

 on account of the great relative development of the stroma. On Dr. 

 Foulis' hypothesis that the first formed layer of follicular epithelium 

 is only modified connective tissue, the development in the rabbit of 

 the inner follicular epithelium from the ovum itself, as I have described 

 it, would be quite incomprehensible, whereas, if both ova and epithelium 

 have a common origin, there would be no morphological absurdity 

 involved in this apparently exceptional mode of development; espe- 

 cially since, as Y. Beneden ( 21 ) and Balfour have shown, the permanent 

 ova are for the most part produced by the fusion of two or more cells 

 (primitive ova), which originate from the germinal epithelium in 

 common with the first formed layer. 



EEFEEEXCES TO LITEEATUEE. 



1. Compare Eimer (" Untersrichungen ueber die Eier der Eeptilien," I. " Arcliiv 



fur Mikroskopische Anatoniie," YIII, p. 218.) 

 2 Eimer (Joe. cit., p. 119) describes actual pores as existing in the much, thickened 



membrane of the germinal vesicle of the ova of some reptiles. 



3. This appearance has been remarked by several observers in hardened ova of the 



fish, reptile, and bird, but evidence is wanting -to prove that it may not be a 

 precipitation effect of the hardening reagent. 



4. The pseudo-nuclei here described are very different in appearance from the yolk- 



nucleus which Dr. Allen Thomson has figured in the ovum of the frog 

 (" Cyclopaedia of Anatomy and Physiology," Article "Ovum," fig. 65b) ; 

 nor do they in any way resemble the " Dotterkerne " and " Dotterschorfe," 

 which Eimer describes in reptilian {loc. cit., pp. 225 and 226) and Balfour 

 in Elasmobranch ova ("Structure and Development of the Vertebrate 

 Ovary," " Quarterly Journal of Microscopical Science," vol. xviii, p. 411). 



5. The systems of fibres here described may be analogous to the pyramidal systems 



