176 INTERNAL SECRETIONS 



to show a first climax of development during embryonic life and 

 a second climax at sexual maturity. So it should be possible 

 to explain the sequence of the phases of puberty by a sequence 

 of phases in the development of the interstitial tissue. One 

 might, indeed, object that synchronously with the development 

 of the interstitial tissue, at the time of sexual maturity, we 

 have also a rapid development of the generative part in the 

 seminiferous tubules, and more or less synchronously with 

 the first appearance of interstitial cells we have the formation 

 of the generative part. But if we take into consideration the 

 fact that a testicle with cells of Sertoli and spermatogonia, but 

 without fully developed interstitial cells, is not capable of 

 producing the internal secretion, we shall understand that, if 

 there is any internal secretion of the testicle during embryonic 

 life, it cannot be due to the primitive generative cells. This 

 will be especially clear if we consider how in the rabbit, for 

 instance, as already mentioned, there is in the first three months 

 no internal secretion of the testicle, although numerous 

 spermatogonia, and even spermatocytes, may be present in 

 the seminiferous tubules. After all it cannot be denied that 

 there is a correspondence between the sequence of changes in 

 the interstitial tissue and the phases of puberty, whereas no 

 such correspondence exists in relation to the phases of sper- 

 matogenesis. In the time between the two great phases ol 

 puberty the interstitial tissue is possibly in an "intermediate" 

 stage, the cells being quiescent. 



The further question arises as to whether also the changes 

 which take place in sexual activity with advancing age are 

 related to changes in the interstitial tissue. 



9. The "Follicular Theory" of Hormone-Production 

 IN THE Testicle. 



If we compare figures 65 and 66, figures 70, 71 and 79, 

 and if we take into consideration only the actual state of the 

 interstitial tissue and of the seminiferous part in all the 

 above-mentioned cases, it is impossible to avoid the conclusion 

 that well developed interstitial cells represent the organ of 

 internal secretion in the testicle of mammals, and that the 

 generative part is not involved in this function. A condition 

 of eunuchoidism may occur in the presence of full spermato- 

 genesis and a normal development of sexual characters may be 



