THE OVUM. 947 



The development of the ovum takes place in the following manner: The surface 

 of the ovary is covered with cylindrical epithelium, the so-called germinal epi- 

 thelium, between which here and there lie round primordial ova (Fig. 358, /, a a). 

 In places the epithelial layer dips down to form tubular depressions in the surface of 

 the^ovary (//) . These tubules, which, according to Waldeyer, are derived from the 

 germinal layer of the ovary, become deeper and deeper, and within them are 

 observed isolated, large globular cells, with nuclei and nucleoli, and also a larger 

 number of smaller parietal cells. These tubes are the ovarian or ovular tubes; 

 the larger round cells are the ova (primitive ova) , the smaller, the epithelial cells 

 of the tubes (/). At the bottom of the tubes the ovular cells, which may undergo 

 mitotic division, predominate. Later on the orifices of the tubes close and the 



Corona , r^ Zona 



, 



:.) Deutoplasra 



Proto- 

 plasm 



\ 

 I \ 



\ 



X 



Germinal vesicle 

 with ameboid 

 germinal spot 

 Perivitelline space 



FlG. 356. A Fresh Ovum from the Ovary of a Woman Thirty Years Old. The side of the vitellus where the ger- 

 minal vesicle is situated is directed toward the observer, who thus looks directly upon the germinal vesicle, 

 which lies upon the deutoplasm. 



tubes are constricted off by the growth of the ovarian stroma into isolated rounded 

 compartments (7, c). Each constricted compartment, which contains usually 

 one, occasionally two ova (IV, o o), becomes a Graarian follicle. The follicles 

 become distended with fluid; their parietal cells become the epithelium of the 

 follicle or the cells of the granulosa, which at particular points surround the 

 ova (IV). Such areas, designated cumuli oophori, are spindle-shaped or 

 cylindrical and consist of several layers ; they produce the zona pellucida. Accord- 

 ing to some observers the yolk also is in part secreted by these cells into the ovule, 

 and a number of the cells are believed to penetrate into the ovum. The follicles, 

 at first only 0.03 mm. in diameter, attain complete development only at the time 



