1 84 



EIGHTEENTH LECTURE. 



Further below, the efferent canal becomes straighter, and 

 its diameter increases to 2 mm. It is now called the vas 

 deferens. Not infrequently, a lateral caecal branch, the vas 



aberrans Halleri, has previously entered 

 it. This is the coarser structure. 



Having become familiar with this compli- 

 cated arrangement, let us investigate the 

 histological texture. 



The seminiferous canals* (Fig. 162) have 

 about the same diameter throughout their 

 entire length. Their diameter is, in most 

 mammals, 0. 1 to 0.25 mm. They are re- 

 markably large in the rat (0.4 mm.). In 

 small animals the walls consist of a single 

 layer of firmly cemented endothelial cells. 

 In larger creatures, this inner layer is sur- 

 rounded by others which show the same 

 construction of flat nucleated scales, but 

 are fenestrated (Mihalkovics). As we shall 

 subsequently return to the parenchyma 

 cells, we merely remark here that the 

 efferent ductuli recti, deviating from these, 

 have a different epithelial lining, namely, 

 cylinder cells. In the rete testis there is 



no gland membrane ; 

 the cells are pavement 

 shaped. Towards the 

 end of the rete, how- 

 ever, commences the 

 cylinder epithelium of 

 the epididymis. 



The quiescent semi- 

 niferous canal is either 

 entirely (Fig. 163, a, 

 b), or, up to a narrow 



Fig. 163. — From the testicle of the calf; a, seminiferous Himetl, ullea Willi 



canals seen in more oblique, b, in more transverse sections ; j j 1 i 



r, blood-vessels ; d, lymphatics. T O U 11 d e d polygonal 



Fig. 162. — Human semi- 

 niferous canal; a, parietes, 

 b, cells. 



WL 



I 



