244 Mr. E. A. Schafer. On Immature Ovarian Ovum [Mar. 18, 



belief that the nuclei are derived from the vesicle, but scarcely by a 

 distinct process of cell- division. At least, I have never been able to 

 detect anything" in the shape of a division- spindle. The only other 

 possible explanation is that the nuclei and cells in question are derived 

 from cells of the follicular epithelium, which are situated in a different 

 plane from that included in the section, and burrow obliquely between 

 the first formed layer and the vitellus of the ovum, imbedding them- 

 selves in the surface of the latter. But this would not account for the 

 sharpness with which they are always marked off from the follicular 

 epithelium, and the fact that both nuclei and cell-substance differ 

 materially in appearance and in their reaction to staining fluids from 

 the nuclei and cell-substance of the first formed layer of epithelium. 



However first formed, they soon multiply and spread around the 

 whole of the ovum, so as to form a second complete layer of follicular 

 epithelium, the cells of which in parts may be two deep. They main- 

 tain for a time their disposition parallel to the circumference of the 

 ovum and transverse to the direction of the cells of the first formed 

 layer (fig. 17). Moreover, they still exhibit the same behaviour 

 towards staining fluids as the vitellus itself. But as the follicle con- 

 tinues to grow, and as the zona jpellucida becomes formed between 

 these cells and the vitellus, they acquire a columnar form with the 

 long axis of the cell perpendicular to the surface of the ovum, their 

 contents clear up, and they come to resemble the cells of the first 

 formed layer in every particular (fig. 20). 



The only statement that I know of which suggests a parallel between 

 these appearances in the rabbit's ovum and others of a similar nature 

 elsewhere occurs in the description which Kuppfer gives of the forma- 

 tion of an inner layer of follicular epithelium (which is said to develop 

 into the test) from nuclei which make their appearance in the peri- 

 pheral layer of the vitellus of the ovum of Ascidia canina ( 16 ). Unless 

 it is permitted to cite the observations of Kleinenberg upon the forma- 

 tion of a layer of cells from the periphery of the ovum of Hydra, which 

 cells take no part in the development of the ovum, but are simply 

 transformed into a capsular envelope ( 17 ).* 



I have not been able to see anything of the kind in the Graafian 

 follicles of other Mammals (cat, dog, man). 



Ovarian Ova of the Bitch. 



The young ova (figs. 27 to 29) have a germinal vesicle which 

 contains a germinal spot and a beautiful intravesicular network. 

 Attached to one side of the germinal vesicle is the main part of the 

 solid substance of the vitellus, and this vitelline mass is connected 



* There is one important difference between these cases and the appearances in 

 the rabbit's ovum above described, viz., that in them the separation of cells from the 

 vitellus occurs after fertilisation. 



