THE RF.PRODUCTTVE SYSTEM 363 



is a spherical cell, luuing a diameter of from 40 to 70,". and the struc- 

 ture of a typical cell. The nucleus or germinal vesicle (so called on 

 account of the part it takes in reproduction) is about half the diameter 

 of the cell and is spherical and centrally placed (Fig. 255). It is 

 surrounded by a double-contoured nuclear membrane, and contains a 

 distinct chromatic network and nucleolus or germinal spot. The 

 cytoplasm is quite easily differentiated into a spongioplasm network 

 and a homogeneous hyaloplasm. Such ova are present in all active 

 ovaries, i.e., during the childbearing period, but are especially numer- 

 ous in the ovary of the infant and child (Fig. 254). 



- e 





^ ■--■.■*• ' ^ -_ - 



Fig. 255. — ^From Section through Cortex of Ape's Ovary. Xiso. (Szymonowicz.) 

 a, Primitive folhcle; b, ovum, with nucleus and nucleolus; c, zona pellucida; d, follicular 

 epithehum; c, follicular cavity;/, ovarian stroma; g, blood-vessel in stroma. 



With the development of the follicle the ovum increases in size 

 and becomes surrounded by a clear membrane, the zona pellucida, 

 believed by some to be a cuticular formation deposited by the egg 

 cell, by others to be a product of the surrounding follicular cells. 

 Minute canals extend into the zona pellucida from its outer surface. 

 These contain processes of the cells of the corona radiata. A narrow 

 cleft, the perivitelline space, has been described as separating the ovum 

 from the zona pellucida. During the growth of the ovum its cyto- 

 plasm becomes coarsely granular from the development of yolk or 

 deutoplasm granules (Fig. 258). Immediately surrounding the 

 nucleus, and just beneath the zona pellucida, the egg protoplasm is 

 fairly free from yolk granules. 



The further maturation of the ovum, which is necessary before the 



