GENERATIVE SYSTEM OF THE FEMALE 



167 



the cumulus), on the surface of which has formed a cell-membrane 

 20 p. thick, hyaline, transparent, and called the zona pellucida 

 (Fig. 54). In proportion as the vesicular or Gfraqfian follicle 

 increases in size and matures, it always comes nearer to the 

 surface of the ovary, and ultimately projects. In the centre 

 of this prominence the follicular wall becomes thin ; the peri- 

 follicular theca disappears, the vessels which supply it atrophy 

 almost completely, and thus is produced a pale translucent spot 

 which is called the stigma. At the part corresponding with the 



FIG. 53. Ovarian follicle in growth, in act of becoming a vesicular follicle, from ovary of rabbit. 

 Magnified 76 diameters. (Chiarugi.) u, ovum with germinal vesicle and zona pellucida ; e, 

 follicular epithelium ; CE, bodies of Call and Exner ; c, principal follicular cavity ; c', small 

 follicular cavities which have not yet united with the principal ; ti, theca interna ; U, theca 

 externa. 



stigma occurs the rupture of the Graafian follicle and the escape 

 of the ovum surrounded by the cells of the cumulus oophorus, 

 which form the so-called corona radiata. The growth of the 

 ovum is shown by the difference in size which it presents at 

 the beginning, when it is contained in the primary follicle, 

 and at the end of its maturity, when it is driven out by the 

 bursting of the folliculus vesiculosus and is provided with the 

 zona pellucida. In the first stage it has a diameter of about 

 25 fi, in the last stage it measures 200 //, (the zona pellucida about 

 10 n, the germinal vesicle 50 /*, and the macula germinativa 5 /*). 

 The mature ovum is about eight times larger than the primordial. 



