THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 



411 



2(b). The cortex of the ovary, as stated above, at first consists of several 

 layers of small, darkly staining cells, among which are many large, clearer sex 

 cells or primitive ova (Fig. 367). From the epithelium, masses or cords of cells 

 grow into the underlying tissue, carrying with them some of the primitive ova. 

 These masses are known as Pfluger's egg cords. In some cases several ova are 

 grouped together, forming egg nests (Fig. 368). The epithelial cells are the 

 progenitors of the follicular cells and constantly undergo mitotic division. The 

 primitive ova, on the other hand, increase in size and their nuclei show distinct 

 intranuclear networks. 



The egg cords become separated from the surface epithelium and are 

 broken up so that in most cases a single ovum is surrounded by a single layer of 



Germinal 

 epithelium 



Cortex 



Fig. 36 



Medulla 



;. — From a section through the ovary of a human foetus of 4 months. Meyer-Ruegg, Buhler. 

 The large cells are the primitive ova. 



epithelial cells. This constitutes a primary Graafian follicle. Rarely a follicle 

 contains more than one ovum. In the case of the egg nests, the ova may become 

 separated, or two or more may lie in one follicle. If two or more ova are 

 present at first in any follicle, usually only one continues to develop and the 

 others either degenerate or are used as nutritive materials. In very rare cases, 

 however, two ova may develop in a single follicle, but whether they reach 

 maturity or not is uncertain. The formation of egg cords is usually com- 

 pleted before birth, but in some cases may continue for one or two years after 

 birth. During the processes thus far described, the stroma also has been in- 

 creasing, and the egg cords and follicles come to be separated by a considerable 

 amount of connective tissue. The germinal epithelium becomes reduced to a 

 single layer of cuboidal cells. 



