344 THE ORGANS 



cells with dark nuclei. These are spermatids which have become free 

 and which degenerate without forming spermatozoa.* 



Separating and supporting the convoluted tubules is a small 

 amount of interstitial connective tissue in which are the blood-vessels 



>^^<^' 



4^ 



; 'V? X--'-'-:"^'^-^^ iv ;-• ; . . #»v />/ V? //'« — /VSJ 





SfC 



Fig. 239. — From Section through Human ^lediastinum and Rete Testis. X96. 

 (Kolliker.) A, Artery; V, vein; L, lymph space; C, canals of rete testis; s, cords of tis- 

 sue projecting into the lumina of the tubules and so cut transversely or obliquely; Sk, 

 section of convoluted portion of seminiferous tubule. 



and nerves. Among the usual connective-tissue elements are found 

 groups of rather large spherical cells w^ith large nuclei — interstitial 



* Tn contrast with the actively functionating seminiferous tubules described above, 

 are the tubules of non-active testes. Typical examples of non-active tubules can be 

 studied in animals having definite breeding' seasons with long intermissions. Here 

 between seasons one finds no spermatozoa in tlu' tubules, no spermatogenesis, only cells 

 of the spermatogone type and Sertoli cells. .\ similar condition is sometimes found 

 in the human testis in senility or after prolonged sickness. In senility there is a 

 general increase in' fibrous tissue at the expense of elastic fibres and cells, while in 

 the tubules sperm cells may entirely disappear, the Sertoli cells alone remaining. 



