GRAAFIAN FOLLICLES 



3 2 9 



protoplasm, the vitellus, a nucleus, the germinal vesicle, and a 

 nucleolus, the germinal spot. Outside the ovum, but not strictly 

 a part of it, is the zona pellucida, a transparent envelope, and 

 outside the zona pellucida a collection of cells, the corona radiata. 

 The perivitelline space is between the ovum proper and the zona 

 pellucida. The zona presents radial striae, which may facilitate 

 the entrance of the spermatozoon. 



Ova are capable of being impregnated as long as 7-9 days 

 after their discharge from the ovary. Their formation begins 

 early in fetal life. The ovum pos- 

 sesses no power of independent 

 motion. It is passive in fecun- 

 dation; it is sought by the male 

 element. Its vitellus, or yolk 

 (protoplasm), contains nutritive 

 non-living material, deutoplasm, 

 whose function is to furnish food 

 substance to the impregnated 

 ovum until the fetal circulation 

 is established. Deutoplasm in 

 the human ovum is scarcely to 

 be distinguished from the living 

 protoplasm, though in the ova 

 of birds, e. g., it is clearly 

 marked off, and constitutes the 



main bulk of the mature egg, since the developing embryo re- 

 ceives no blood from the mother. 



Graafian Follicles. The Graafian follicles are directly con- 

 cerned in the development and maturation of ova. These are 

 small vesicles in the cortical ovarian substance surrounded by a 

 capsule of thickened ovarian stroma, the tunica vasculosa. In- 

 side the tunica vasculosa, lining the spherical cavity of the ves- 

 icle, are several layers of epithelial cells making up the membrana 

 granulosa. The cavity is filled with an albuminous liquid, the 



V 



FIG. 93. Ovum. (From Yeo 

 after Robin.) 



a, zona pellucida and yitelline mem- 

 brane; b, yolk; c, germinal vesicle or 

 nucleus; d, germinal spot or nucleolus; 

 e, interval left by the retraction of the 

 vitellus from the zona pellucida. 



