THE DEVELOPMENT OF THE UROGENITAL SYSTEM. 407 



numerous sex cells in various stages of differentiation (Fig. 367). The 

 rete cords which arise in the cranial end of the "indifferent" gland (p. 404) 

 come to lie in what will be the hilus of the ovary. The ovary may thus be 

 said to be composed of two parts (i) the rete anlage and (2) the stratum ger- 

 minativum. The latter is subdivided by the albuginea into (a) medulla and 

 (b) cortex. 



i. The rete cords develop into a group of anastomosing trabeculae which con- 

 stitute the rete ovarii, situated in the hilus but nearer the cephalic end of the 

 gland (Fig. 366). They are the homologues of the rete testis. The cells com- 

 posing them are smaller and darker than those of the medullary cords. Sprouts 

 grow out from the rete cords and unite with the medullary cords and the meso- 

 nephric tubules. (The same process occurs in the testicle, where the rete cords 

 give rise to the functional rete testis and straight seminiferous tubules.) In 



Cortex :^R**.v, '.'*\\ V"- f&.f-'r'Ji^^^^m^^. Mesothelium 



(Germinal epithelium) 



Medulla -i 



Mesovarium 



Re te ovarii 



FIG. 367. Transverse section of the ovary of a fox embryo. Biihler in Hertwig's Handbuch. 

 The large clear cells are the primitive ova. 



some of the cords lumina appear and are lined with irregular epithelium. 

 Such a condition represents the height of their development in the ovary. 

 From this time on, they degenerate and finally disappear. The time of their 

 disappearance varies in different individuals; they usually persist until birth, 

 sometimes until puberty. 



Formerly it was thought that the rete cords were derived from the meso- 

 nephric tubules and entered the genital glands secondarily. More recent re- 

 searches have demonstrated quite conclusively, however, that they are deriva- 

 tives of the germinal epithelium and unite with the mesonephric tubules 

 secondarily. 



2 (a). The medullary cords are composed of small epithelial cells, contain a 

 number of larger sex cells or primitive ova, and are surrounded by stroma 

 (Figs. 367, 368). They are connected with the rete cords and in some places 

 with the germinal epithelium. During foetal life they give rise to primary 

 ovarian (Graafian) follicles; later they degenerate and finally disappear. 



