INTERNAL SECRETION OF TESTICLE 185 



Conclusions. 



The experiments recorded in the preceding sections supply 

 evidence that in mammals 



(i) Underdevelopment of interstitial cells is connected with 

 eunuchoidism. 



(2) Signs of castration are absent when the seminiferous 

 tubules undergo manifold changes, and even when the tubules 

 undergo retrograde development to the infantile stage, provided 

 that the interstitial cells are fully developed. 



(3) Complete sexual maturity is possible even when 

 spermatozoa were never present in the testicle. 



(4) On the other hand, eunuchoidism is not excluded in the 

 presence of spermatozoa. 



It follows that in mammals 

 (a) the interstitial cells are a necessary part of the endocrine 



apparatus of the testicle; 

 {b) no proof exists of a direct hormonic action by the cells of 

 Sertoli or by other constituents of the wall of the tubules 

 independently of the interstitial cells. 



It might be assumed as a working hypothesis that the 

 transformation of the interstitial cells after birth into an 

 endocrine apparatus is connected with spermatogenesis 

 ("follicular theory") or with some stages of this process. 



It is probable that the hormonic apparatus of the testicle 

 in man and other mammals during ontogenetic development 

 reaches a culminating point .twice; the first in embryonic 

 development, the second at the time of puberty. It is certain 

 that in the rabbit the endocrine apparatus does not function 

 in the first three months after birth, and it is possible that in 

 man also the hormonic apparatus of the testicle is, until puberty, 

 in such an "intermediate" state, when the secretory activity 

 of the interstitial cells is much reduced or even ceases 

 completely; the latter is the more probable. 



What we generally call the "age of puberty'' is on this view 

 really the second great phase of puberty. The first great phase of 

 puberty should be placed at the time of embryonic development 

 when the embryonic asexual or indifferent soma turns over to 

 the male side. An intermediate phase of puberty may be said 

 to occur between the first and the second great phases ; it is the 



