CHANGES IN THE OVARY 117 



Nagel, 1 and van Winiwarter, 2 have followed Waldeyer in suppos- 

 ing that the follicular epithelial cells (which form the innermost 

 layer of the wall of the Graafian follicle) are derived like the ova 

 from the germinal epithelium. Schafer described appearances 

 indicating the possibility of the innermost layer of follicular 





^* **'$&$* 



m 



r' 



FIG. 22. Cortex of pig embryo, showing germinal epithelium, Pfluger's 

 tubes with ova in various stages of development. (From Williams' 

 Obstetrics, Appleton & Co.) 



epithelium being derived from the ovum itself ; but, as he himself 

 pointed out, this view does not involve any morphological ab- 

 surdity if the ova and follicle-cells have a common origin. Balfour 

 described protoplasmic masses of embryonic ova in which the 

 cells appeared to be united together in such a way as to suggest 



1 Nagel, " Das menschliche Ei," Arch. f. Mikr. AnaL, vol. xxxi., 1888. 



2 Van Winiwarter, " Recherches sur 1'Ovogenese," &c., Arch, de Biol,, 

 vol. xvii., 1901. 



