THE FEMALE REPRODUCTIVE ORGANS. 



227 



FIG. 268. 



to its surface, forming a radial zone, the corona radiata. The 

 interior of the follicle is occupied by an albuminous fluid, the 

 liquor folliculi, derived probably as an exudate from the blood- 

 vessels of the theca, as well as from the breaking down of some of 

 the central cells of the follicle. 



Within the discus proligerus lies the ovum, a spherical body about 

 . 2 mm. in diameter, enclosed within a distinct membrane, the zona 

 pellucida, which presents a delicate radial striation. These mark- 

 ings are regarded by many as due to the presence of fine canals, 

 which may facilitate the access 

 of fluids and possibly, also, of 

 the spermatozoa to the contained 

 cell. The zona pellucida is a 

 protecting membrane, derived 

 from the cells of the surrounding 

 discus proligerus, and does not, 

 strictly considered, constitute a 

 part of the ovum proper, since 

 it lies outside of the true cell- 

 wall, the vitelline membrane. 



The protoplasm of the ovum, 

 or vitellus, occupies almost the 

 entire area within the zona pellu- 

 cida, and is limited by the delicate 

 and inconspicuous vitelline mem- 

 brane, which closely approxi- 

 mates the inner surface of the 

 zona pellucida. The protoplasm of the ovum is modified by the 

 presence of numberless particles of fatty matter which lie embedded 

 within the albuminous protoplasm proper. The germinal vesicle, 

 corresponding to the nucleus of the ovum, is situated eccentrically, 

 limited by a distinct membrane, and contains the germinal spot or 

 nucleolus. Of the parts of the ovum, the germinal vesicle is the 

 most important, since in it, as in the nucleus of cells in general, are 

 inaugurated the important changes attendant upon the phenomena 

 of cell division. The threads of chromatin form a loose, irregular 

 net-work throughout the germinal vesicle, the interspaces of which are 

 filled with a substance representing the nuclear juice. While each 

 Graafian follicle contains, as a rule, but a single ovum, exceptions 

 are observed occasionally where two, and even three, ova are found 

 within the same vesicle. 



The formation of new follicles continues for only a short time 

 after birth ; ovisacs are then most numerous, the entire number 

 contained within the two ovaries of the child being estimated at over 



Ovum from ovary of cat : d, innermost cells of 

 discus proligerus, between which processes from 

 zona pellucida (z) extend ; in, vitelline membrane ; 

 v, vitellus ; g, germinal vesicle ; s, germinal spot. 



