INTERNAL SECRETION OF TESTICLE 173 



of May and concomitantly the secretion of the epidi(i5miis 

 ceases. From all these observations, and likewise from those 

 on other mammals with a periodic spermatogenesis (1923 b), 

 Courrier concludes that the cyclic changes of the interstitial 

 gland are in a striking correspondence with the cyclic changes 

 of the sex characters. The cells of Sertoli, however, also under- 

 go concomitant changes. On the contrary, the accessory 

 genital glands may be in a state of rest when the seminal tubules 

 are active. 



The statements of Regaud, Tandler and Gross on the mole 

 disagree with those made about the hedgehog, the woodchuck 

 and the bat. They are also opposed to the view that heat is 

 caused by an increased activity of the interstitial tissue. But, 

 as already mentioned, the statements of Lecaillon about the 

 mole are somewhat different from those of the other authors. It 

 is also possible that the decrease of the interstitial tissue in the 

 mole during heat is only an apparent one. The nearer the time 

 of heat, the greater the room occupied by the seminiferous 

 tubules in the testicle and the greater also the space in which the 

 interstitial cells are distributed. If the total volume of the 

 interstitial tissue is not increased in the same measure as the 

 total volume of the seminiferous tubules, a microscopical 

 preparation will give the impression that the interstitial tissue 

 is reduced, even though in reality there is a very marked 

 increase of the latter. One will understand the weight of such 

 an objection, if one takes into consideration how enormously 

 the volume of the testicle is increased in heat owing to the 

 augmentation of the tubules. As said already in the first 

 edition of this book, it is absolutely necessary to know the 

 real number of interstitial cells, or the real volume of the 

 interstitial tissue in the testicle during heat and during sexual 

 inactivity; we learn nothing about this question when we 

 merely count the cells in one or another preparation. We 

 shall meet with the same difficulties in dealing with amphibians 

 as we here encounter in mammals (see below in this chapter). 



Tandler and Gross concluded from their observations that 

 the interstitial cells play a leading role in causing the condition 

 of heat. They suggested that the interstitial cells are a factor 

 in the spermatogenesis of the next heat, influencing the 

 generative part of the testicle as they influence the somatic 

 characters. If this were true, it would follow that the generative 



