216 



THE UROGENITAL SYSTEM 



single cellular mass in man, cords, or Tfluger's tubes,' never growing in 

 from the epithelium. Generally it has been believed that the primary 

 follicles are derived from the subdivision of such cords. 



Coincident with the origin of a new zone of cells at the periphery of 

 the ovary, goes the degeneration of young ova in, the medulla. By the 

 ingrowth into this region of connective tissue, the ova are separated into 

 clusters, or cords, the genital cells of which all degenerate, leaving in the 



Primordial egg 



Germinal epithelium 



Primordial ovum 



Blocd -vessel 



Primordial ova 



FIG. 228. Ovary of five-months' fetus, showing primordial follicles (De Lee). 



medulla only a stroma of connective tissue. Late in fetal life, indifferent 

 cells, by surrounding the young ova of the cortex, produce primordial 

 follicles (Fig. 229 A}. During the first year after birth the primitive 

 follicles are transformed into vesicular (Graafian) follicles. By cell divi- 

 sion, the follicle cells form a zone many layers deep about the young 

 ovum (Fig. 229 B}. Next, a cavity appears in the sphere of follicle cells; 

 it enlarges, and produces a vesicle filled with fluid (Figs. 4 and 230). The 

 ovum is now located eccentrically and the follicle cells directly surrounding 

 it constitute the cumulus oophorus (egg-bearing hillock). About the 

 stratum granulosum, formed by the original follicle cells, there is differen- 

 tiated from the stroma of the ovary the theca jolliculi. This is composed 



