202 NORMAL HISTOLOGY. 



highly developed type, we recognize four structural 

 elements: i, a thick hyaline membrane, presenting, 

 with high powers, a delicate radial striation, and 

 called the zona pellucida ; 2, within the zona pellu- 

 cida is the cell-body, consisting of coarsely and 

 finely granular protoplasm, and usually called the 

 vitellus ; 3, the vitellus encloses a comparatively 

 large vesicular, transparent, and sharply-outlined 

 nucleus, the germinal vesicle ; 4, the germinal vesicle, 

 which is usually somewhat eccentrically placed con- 

 tains, in addition to a nearly transparent fluid, a 

 small dark, often almost opaque nucleolus, the 

 gcnninative spot. 



As the Graafian follicles mature, they approach the 

 surface of the ovary, often projecting above it ; the 

 walls become thinner and less vascular at the pro- 

 jecting side, and finally burst at a menstrual period. 

 The ovum, with the fluid and a portion of the fol- 

 licular epithelium, is discharged, and through the 

 hemorrhage which occurs from the capillaries in the 

 follicular wall, the cavity becomes filled with blood. 



Changes now occur in the walls and cavity of the 

 follicle, which result sooner or later in cicatrization 

 and obliteration of the cavity. These changes vary 

 considerably, depending upon whether or not the 

 ovum is impregnated and develops ; and the differ- 

 ence expresses itself chiefly in a difference in size 

 and persistence of the mass of tissue called the cor- 

 piis luteum, which is produced by a growth of certain 



