CHAP. XX.] FEMALE GENERATIVE ORGANS. 249 



The stroma contains many blood-vessels and lymphatics. The 

 outer portion is more condensed than the interior, and the whole 

 is covered by a peculiar layer of columnar epithelium-cells, 

 called germinal epithelium. 



The Graafian follicles are cavities dotted about in the stroma 

 in large numbers. The smaller ones lie near the surface. The 

 larger are more deeply embedded, and only approach the sur- 

 face when they are ready to discharge their contents. The 

 follicles have each their own proper wall or tunic, derived from 

 the connective tissue of the stroma, and each is lined by a layer 

 or layers of granular epithelium-cells, and contains an ovum. 

 The granular layer of cells, closely lining the cavity of the follicle, 

 is termed the membrana granulosa, but at one or other side it is 

 heaped up into a mass of cells which projects into the cavity of 

 the follicle and envelops the ovum. This mass of cells which 

 immediately surrounds the ovum is called the discus proligerus. 



As the follicle matures, fluid collects in the cavity, and, in- 

 creasing in amount, the follicle gradually becomes larger and 

 more tense. It now approaches the surface and begins to form 

 a protuberance like a small boil upon the outside of the ovary. 

 Finally the wall of the ovary and the wall of the follicle burst 

 at the same point, and the fluid (liquor folliculi) containing the 

 ovum, with the loose, irregular mass of cells, the discus pro- 

 ligerus, clinging to it, is set free. At the moment of rupture, 

 the ovum is received by the Fallopian tube and afterwards con- 

 veyed to the uterus. After the follicle has discharged its con- 

 tents, it has done its work, and it passes through a series of 

 degenerative changes, and eventually disappears. Thus in the 

 same ovary some of the follicles are mature, or approaching 

 maturity; others are undergoing development; while others 

 are retrograding and disappearing. 



The ova are formed from the germ-epithelium on the surface 

 of the ovary, the cells of which become enlarged and dip down 

 into the stroma in the form of little elongated masses. From 

 these groups of cells the Graafian follicles and the ova are pro- 

 duced. The ovum is a single cell about y|^ inch (0.203 min.) 

 in diameter. It has (1) a thick, surrounding envelope or 

 membrane, called the vitelline membrane or zona pellucida ; 

 (2) within the membrane or cell- wall is the protoplasm of 

 the cell, filled with fatty and albuminous granules, and usually 



