354 



REPRODUCTION 



of the follicle is due to the prohferation of the epithelial 

 cells. These eventually form two layers — the memhrana 

 granulosa hning the cavity and the discus proligerus cover- 

 ing the ovum. These two layers become partly separated 

 by the gradual accumulation of fluid — liquor folliculi. 

 Hypertrophic changes simultaneously occur in the fibrous 

 sheath, in which two layers become recognisable — theca 

 externa and theca interna. 



Fig. 65. — Section of cat's ovary (Schron), from Schafer's Essentials of 

 Histology, after Quain : 1, gemiinal epithelium ; 5, Graafian 

 follicles in their earliest stages ; 6, 7, 8, more advanced follicles ; 

 9, almost mature follicle; 10, corpus luteum. 



The ripe folhcle has a diameter of 15 mm. and protrudes 

 from the surface of the ovary. 



The ovum consists of a single cell containing nucleus and 

 nucleolus. It is surrounded by a thin membrane — the 

 vitelline membrane, around which is the zona radiata, a 

 radially striated structure which is supposed to contain 

 fine canals through which the ovum is nourished. 



The growth of the follicle culminates in its rupture, the 

 ovum, surrounded by the discus proUgerus, being dis- 

 charged into the peritoneal cavity. This process, which 

 is known as ovulation, occurs regularly at oestrus in most 



