THE REPRODUCTIVE ORGANS 71 



assigned to them, and they may possibly be responsible for the 

 internal secretion just referred to. 



There is an important difference in the result obtained when 

 the whole cord is ligatured from that obtained when the vas 

 only is tied. In the former case all sexual activity comes to 

 an end ; in the latter, after a short interval of time, the animal 

 remains just in the same condition as the control, although, of 

 course, reproduction is impossible in both cases. After ligature 

 of the vas the interstitial cells remain unaltered, although the 

 spermatogenic tissue degenerates. These results, pointing 

 distinctly to an internal secretion on the part of the interstitial 

 cells of the testis, have been furnished to me by Dr. Copeman. 

 His results are generally in agreement with those of Bouin and 

 Ancel. 



^ Foges in 1899 could not be sure that transplantation of the 

 testis had any influence on the secondary sexual characters. 

 In a later paper he states a different conclusion. The experi- 

 ment he performed was to remove the testes of fowls and 

 transplant them to abnormal positions in the body cavity. In 

 these later experiments at any rate, in those which were 

 successful, the transplanted testes had a similar influence upon 

 the development of the secondary sexual characters to that of 

 Jbhe normally placed testes, and the comb and spurs were 

 developed just as in uncastrated cocks. From these experi- 

 ments Foges draws the conclusion that the testes are organs 

 furnishing an internal secretion which controls the develop- 

 ment of the male characters. 



Shattock and Seligmann have also performed some experi- 

 ments upon testicular transplantation in fowls. They report 

 that the secondary sexual characters develop to a varying 

 extent, which seem to depend on the amount of testicular 

 substance left behind. 



It has been alleged that the development of male characters 

 followed the injection of extracts of testis. The injections 

 were made into hens, and the combs and wattles grew in size, 

 and became more brightly coloured. These experiments 

 require confirmation. 



Very important indeed, as bearing on the question of the 

 internal secretion of the testes, are the experiments of Nuss- 

 baum. At the approach of the breeding season there is formed 

 in the male frog a thickened pad of skin on the first digit of each 



