774 



THE REPRODUCTIVE ORGANS 



These ova are descended from primitive germ cells which become differ- 

 entiated very early in the embryo. In some vertebrates, such as the chick, 

 there is evidence that the primitive germ cells become distinct from all other 

 cells in the body even before the formation of the embryonic mesoderm has 

 been completed. Later they become located in a membrane of short colum- 

 nar cells, the so-called germinal epithelium, covering the surface of the embry- 

 onic ovary. 



The Graafian follicles of the human ovary are formed in the following 

 manner: The cells of the germinal epithelium undergo proliferation so as 

 to form several strata, and grow into the ovarian stroma as longer or shorter 



Downgrowths of epithelium Ovum with its investing cells 

 Germinal epithelium 



Stratum granulosum 



Epithelial cells Ovarian strorna Graafian follicle 



Ovum 



Liquor folliculi 

 Discus proligerus 



FIG. 494. A, Diagrammatic Representation of the Manner in which the Vesicular 

 Ovarian Follicles Arise During the Development of the Ovary. B, Diagram Illustrating 

 the Structure of a Ripe Vesicular Ovarian Follicle. (Cunningham.) 



columns or tubes. By degrees these tubes become cut off from the surface 

 epithelium, and form cell nests, small if near the surface, larger if in the depth 

 of the stroma. The nests increase in size from multiplication of their cells. 

 Inside these nests, certain cells which are descended from the primitive germ 

 cells enlarge and form ova. The small cells of a nest surround the ova, and 

 form their membrana granulosa, and the stroma growing up separates the 

 surrounded ova into so many Graafian follicles. 



The smallest follicles are formed at the surface, and make up the cortical 

 layer. It is said by some that the superficial follicles as they begin to ripen 

 become more deeply placed in the ovarian stroma; and, again, that as they 

 increase in size they make their way back toward the surface. The develop- 

 ment of all eggs that are destined to mature is carried as far as the early fol- 

 licular stage in the ovary of the child, previous to the birth of the child, or 

 within a relatively short period thereafter. Conditions indicative of the for- 



