INTERNAL SEXUAL TRANSFORMATIONS OVARY 



215 



unite to form septula which extend from the mediastinum testis to the 

 tunica albuginea. The latter becomes a relatively thick layer in the adult 

 testis and is so called because of its whitish appearance. 



Differentiation of the Ovary. -The primitive ovary, like the testis, 

 consists of an inner epithelial mass bounded by the parent peritoneal 

 epithelium. The ovarian characters appear much more slowly than those 

 of the testis. In fetuses of 50 to 80 mm. (C H), the inner epithelial mass, 

 composed of indifferent cells and primordial germ cells, becomes less dense 

 centrally and bulges into the mesovarium (Fig. 227). There may be dis- 

 tinguished a dense, outer cortex beneath the epithelium, a clearer medul- 



Tubules of mesonephrc 

 (Paroophoron) 



Ligamenlunt ovarii 



Uterine (Mul- 

 lerian) tube 



Primordial 

 germ cells 



Medulla 



Cortex . 



FIG. 227. Section of an ovary from a 65 mm. human fetus. X 44. 



lary zone containing large germ cells, and a dense, cellular anlage in the 

 mesovarium, the primitive rete ovarii, which is the homologue of the rete 

 testis. No epithelial cords and no tunica albuginea are developed at this 

 stage, as in the testis. 



Later, three important changes take place: (i) There is an ingrowth 

 of connective tissue and blood vessels from the hilus, resulting in the forma- 

 tion of a mediastinum and septula. (2) Most of the cells derived from the 

 inner epithelial mass are transformed into young ova, the process extend- 

 ing from the rete ovarii peripherally (Fig. 227). (3) In fetuses of from 80 

 to 1 80 mm. (C R) length, the ovary grows rapidly, owing to the formation 

 of a new peripheral zone of cells, derived perhaps in part from the peri- 

 toneal epithelium. At the end of this period the septulae line the epithe- 

 lium with a fibrous sheath, the anlage of the tunica albuginea. Hereafter, 

 although folds of the epithelium are formed, they do not penetrate beyond 

 the tunica albuginea, and all cells derived from this source subsequently 

 degenerate. This new peripheral zone, according to Felix, is always a 



