104 PHYSIOLOGY OF FARM ANIMALS [CH. XII. 



the spermatogenetic tissue underwent degeneration owing to the 

 semen being unable to escape. The same effect is brought about 

 by exposing the testes to the influence of Rontgen rays, as has 

 been shown more especially by experiments on roe-deer b}' Tandler 

 and Gross. On the other hand, the interstitial cells of the testis 

 were not affected in anj' of these experiments, and the develop- 

 ment of the secondary sexual characters (growth of horns, etc.) 

 must be correlated with the persistence and functional activity 

 of these cells. It must be concluded therefore that the interstitial 

 cells are responsible for the secretion of the testicular hormone. 



Further experiments have shown that unilateral castration in 

 Herd wick rams does not affect the symmetry of horn growth, 

 while, according to Ribbert, there is evidence that removal of one 

 testis may be followed by compensatory hypertrophy on the part 

 of the other. 



