12 THE HUMAN BODY. 



These are lined by cells, and each contains a single ovum. 

 Deeper in, larger follicles (7, 8, 9, Fig. 164) are seen, their 

 cavities being distended, during life, by liquid: in these the 

 essential structure may be more readily made out. Each 

 has an external fibrous coat constituted by a more dense 

 layer of the ovarian stroma; within this come several layers 

 of lining cells (9, a, Fig. 164) constituting the membrana 

 granulosa. At one point, b, the cells of this layer are heaped 

 up, forming the discus prohgerus, which projects into the 



FIG. 164. A section of a Mammalian ovary, considerably magnified. 1, outer 

 capsule of ovary; 2, 3, 3', stroma; 4, blood-v'essels; 5. rudimentary Graafian fol- 

 licles; 6, 7, 8, follicles beginning to enlarge and mature, and receding from th& 

 surface; 9, a nearly ripe follicle which is again traveling towards the surface 

 preparatory to discharging the ovum; a, membrana granulosa; b. discus pro- 

 ligerus; c, ovum, with, d, germinal vesicle and. e. germinal spot. The general 

 cavity of the follicle (in which 9 is printed) is filled with liquid during life. 



liquid filling the cavity of the follicle. In the discus proli- 

 gerus the ovum, c, lies, having in it a nucleus or germinal 

 vesicle, d, and a nucleolus or germinal spot, e. The ovum 

 is about 0.2 mm. ( T | inch) in diameter; its structure is 

 better represented at A, Fig. 8*, where iHs seen to consist 

 of a thick outer coat or cell-wall, a, called the vitelline 

 membrane or zona pellucida; within which is the granular 

 cell protoplasm, called here the vitellus or yelk; and in that 

 again the germinal vesicle and spot. 



* Page 26. 



