THE GENITAL GLANDS AND DUCTS — TESTIS 



213 



of the rabbit and pig are formed as active ingrowths of cellular cords from the 

 epithehum. 



The testis cords soon become rounded and are marked off by connective 

 tissue sheaths from the intermediate cords, columns of undifferentiated tissue 

 which he between 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 indiferent cells with a few larger genital 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 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 



Mesorckium 

 Intermediate <oid 



Rete testi 



Genital cell - 



Durlns deferens 



RpillKlium 



Tunica albuginea 



Testis cord 





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



the testis tubules anastomose and form the tubuli contorti. Their proximal por- 

 tions remain straight as the tubuli recti. The rete testis becomes a network of 

 small tubules which finally unite with the collecting tubules of the mesonephros 

 (see p. 218). 



The primitive genital 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 becom.e the sus- 

 tentacular cells (of Sertoli) of the adult testis. Primitive genital cells of the inter- 

 mediate cords 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 themselves are resorbed, but the connective tissue 

 sheaths of the tubules unite to form septula which extend from the mediastinum 



