212 



NORMAL HISTOLOGY. 



and the inner clear zone forms the delicate hyaline envelope invest- 

 ing the middle-piece and the tail. 



Embedded within the loosely laminated intertubular connective 

 tissue, groups of polyhedral nucleated cells occur in greater or less 

 profusion ; these interstitial cells are present within the testicle of 

 man and of mammals generally. But within the interstitial tissue of 

 the boar's testicle they are found in remarkable abundance. The 

 elements, evidently epithelial in nature, are arranged in groups or 

 cylinders in the interstices between the seminiferous tubules, and 

 represent the remains of the epithelial structures of the fostal Wolffian 

 body. 



With the termination of the convoluted division of the seminifer- 

 ous tubules the secreting tissue of the gland ends, since the con- 

 tinuation of the seminal canals, effected by the straight tubes and 

 those forming the rete testis, represents the beginning of the elabo- 

 rate system of excretory ducts extending from the testicle to the 

 urethra. 



On arriving at the straight canals the seminiferous tubules be- 

 come reduced in size (20-30 //), as well as in number, the thick 

 epithelial lining of the convoluted division being replaced by a single 



layer of low colum- 



FIG. 257. nar cells. The short 



narrow tubuli recti 

 occupy the apices of 

 the pyramidal lobules, 

 and enter the medias- 

 tinum, where they open 

 into the irregular canals 

 of the rete testis. The 

 latter vary in size from 

 mere clefts to channels 

 approaching in diam- 

 eter that of the convo- 

 luted tubules ; they are 

 lined by a single layer 

 of flattened epithe- 

 lial plates. 



Section of tubule of human epididymis : a, membrana pro- Beginning at the Up- 



pria ; b, columnar cells crowned with zone of long cilia (c) ; d, j r ., f t 

 layer of non-striped muscle ; e, intertubular areolar tissue ; s, 



masses of spermatozoa occupying lumen of tube. tis, the further COUTSC 



of the seminal canal is 



effected by the ten to fifteen vasa efferentia, which, by their pro- 

 gressively increasing convolutions, form as many conical lobules, the 

 coni vasculosi, the aggregate of which makes the globus major 



