196 INTERNAL SECRETIONS 



the testicle in many birds increases to a very considerable 

 degree. (For details see Marshall, 1922, p. 22). Loisel (1902 b) 

 recorded that in the house sparrow and in another species of 

 sparrow from Madagascar the spermatogenetic cells and the 

 cells of Sertoli, when heat is approaching, are full of fatty 

 granules, whereas no signs of secretory activity are to be seen 

 in the interstitial cells. From these and similar observations 

 on other species of birds Loisel concluded that the endocrine 

 function of the testicle must be ascribed to the spermato- 

 genetic cells and to the cells of Sertoli, and that heat is brought 

 about by the endocrine function of these cells only, not by that 

 of the interstitial cells. But, on the other hand, Loisel himself 

 mentioned that in the canary fatty granules occur also in the 

 interstitial cells, which are present in small numbers. Further, 

 Loisel observed signs of secretory activity in the interstitial 

 cells of the sparrow during embryonic development. Long 

 before the formation of seminiferous tubules, long before the 

 sexual differentiation of the sexual gland, he found interstitial 

 cells packed full with fatty granules besides the cells of the 

 germ epithelium. But he records that these cells eventually 

 decrease in number and disappear finally in the testicle of the 

 adult (1902 a). 



Observations on the interstitial cells in the testicle of the 

 silver and the golden pheasant have been made by Pezard. 

 Before puberty the interstitial cells are very numerous, but 

 as in the cock they disappear almost completely when the 

 first spermatogenesis is completed, i.e., when puberty is at- 

 tained; this takes place during the first great moult in spring 

 and summer. Observations on the interstitial cells of the 

 pheasant are all the more interesting as the sexual behaviour of 

 this bird undergoes cycHc changes from the time of rest to that 

 of heat. Pezard stated that in the golden pheasant the inter- 

 stitial cells again increase in number during sexual inactivity 

 when the generative part of the testicle assumes an almost 

 embryonic appearance. But I think that here we have to do 

 with an apparent change in the number of the interstitial cells. 

 This is why I do not agree with Pezard, who thinks that in 

 birds the interstitial cells are merely a factor in spermato- 

 genesis, whereas the other sexual characters of birds are 

 formed and preserved, according to Pezard, by an hormonic 

 action of the spermatogenetic cells or of the cells of Sertoli. 



