214 



THE UROGENITAL SYSTEM 



of the rete testis. Two or three layers of loosely arranged cells between the 

 testis cords and the epithelium constitute the anlage of the tunica albugin- 

 ea. On the contrary, Allen (1904) holds that the testis cords of the rabbit 

 and pig are formed as invaginations of the surface epithelium. 



The testis cords soon become rounded and are marked off by connec- 

 tive-tissue sheaths from the intermediate cords, columns of undifferentiated 

 tissue which lie beteen them (Fig. 226). Toward the rete testis the sheaths 

 of the testis cords unite to form the anlage of the mediastinum testis. The 

 testis cords are composed chiefly of indifferent cells with a few larger germ 

 cells. The cells gradually arrange themselves radially about the inside of 

 the connective-tissue sheath as a many-layered epithelium, in which, 

 during the seventh month, a lumen appears. The lumina appear in the 



Mesorchium 

 Intermediate cords 



Rete 



Ductus deferens 



Epithelium 



Tunica albuginea 



Testis cord 



Primordial 

 germ cell 



FIG. 226. Section through the testis of a 100 mm. human fetus. X 44. 



peripheral ends of the testis cords, and, extending toward the rete testis, 

 meet lumina which have formed there. Thus the solid cords of both are 

 converted into tubules. The distal portions of the testis tubules anasto- 

 mose and form the tubuli contorti. Their proximal portions remain 

 straight, as the tubuli recti. The rete testis becomes a network of small 

 tubules that finally unite with the collecting tubules of the mesonephros 

 (seep. 219). 



The primordial germ cells of the testis cords form the spermatogonia 

 of the spermatic tubules, and from these at puberty are developed the 

 later generations of spermatogonia (p. 14). The indifferent cells of the 

 tubules become the sustentacular cells (of Sertoli) of the adult testis. Cer- 

 tain cells of the intermediate cords, epithelial in origin, are transformed 

 into large, pale cells, which, after puberty, are numerous in the interstitial 

 connective tissue and hence are called interstitial cells. The intermediate 

 cords, as such, disappear, but the connective-tissue sheaths of the tubules 



