172 INTERNAL SECRETIONS 



tissue attains its minimum during hibernation or in the time 

 of sexual inactivity, and that it attains its maximum during 

 heat. Marshall concluded from his experiments that the 

 characteristic features during heat are caused in the hedgehog 

 by an increased internal secretion of the interstitial cells. 



In disagreement with the statements concerning the wood- 

 chuck and the hedgehog are those relating to the mole. The 

 mole experiences heat once in the year about the beginning of 

 March, and at this time the generative part of the testicle 

 attains its maximum. Regaud found the interstitial tissue 

 well developed in June and July, when the generative part is 

 already at its minimum. In December only a few interstitial 

 cells are to be found ; at the same time the tubules enter upon 

 new spermatogenesis. The statements of Lecaillon on the mole 

 are somewhat different from those of Regaud, as seen in the 

 diagram. Finally a detailed investigation on the cyclic changes 

 in the testicle of the mole was made by Tandler and Gross 

 (1912, 1913, p. 117)- Their results were again somewhat 

 different from those of Regaud and Lecaillon as concerns the 

 time of development of the interstitial tissue. They stated 

 that the maximum of the generative part corresponds to the 

 minimum of the interstitial tissue, this being reduced at the 

 period of heat. In the time of sexual inactivity, in the autumn, 

 when the generative part is at its minimum, the interstitial 

 tissue attains its maximal development. Tandler and Gross 

 never found mitoses in the interstitial cells when at their 

 maximal number,- and they suggested that the connective 

 tissue cells in the testicle are mostly inactive interstitial cells, 

 which can be activated at a given moment and assume the 

 morphological character and the function of interstitial cells. 

 Evidently the cyclic increase of the number of interstitial 

 cells does not imply a cyclic proliferation of cells. 



Courrier (1923 a) made an investigation on the cyclic changes 

 in the bat. He insists on the very important fact that the 

 generative part of the testicle is inactive during the autumn 

 and winter, and, nevertheless, the accessory genital glands (the 

 epididymis, the vas deferens, the seminal vesicles and the 

 prostate) are in full secretory activity; likewise sexual inter- 

 course can take place during that time. The interstitial cells 

 have at that time the appearance of highly active glandular 

 cells. The interstitial cells undergo a pigmentation at the end 



