216 R. R. HUMPHREY 



Hanseman ('95), the earliest worker in this field, reported few 

 or no interstitial cells present in the marmot during hibernation, 

 when spermatogenesis is not active. In the spring, after several 

 weeks of active life and the resumption of spermatogenesis, they 

 are greatly increased in numbers. Ganfini ('03), on the other 

 hand, declared the interstitial cells of the marmot during hiberna- 

 tion to be fully as numerous as during the animal's active period, 

 but to be smaller and of different structure and staining reactions. 

 He did not consider these differences as in any way correlated 

 with spermatogenesis, but thought them due to changed condi- 

 tions of metabolism, such as might affect any other tissue during 

 hibernation. 



Regaud ('04), Lecaillon ('09), and Tandler and Grosz ('11) 

 worked on the testis of the mole (Talpa europea). They found 

 that spermatogenesis goes on during the autumn and winter 

 months, during which time the interstitial cells are at their 

 minimal size and number. After the spermatozoa leave the 

 testis in March, the tubuli contorti become reduced in size, while 

 the interstitial cells increase greatly in size and number, their 

 vacuolated cytoplasm at this time indicating the presence of 

 lipoids. With the increase in spermatogenesis in the early 

 autumn, a reduction in the size and number of interstitial cells 

 occurs. 



Marshall ('11), examining the testes of hedgehogs (Erinaceus 

 europeus), found no spermatogenesis during winter, but a rapid 

 enlargement of the testis in the spring preceding the rutting 

 period, this enlargement being due to growth of the interstitial 

 tissue even more than to increase in size of the tubules. Regres- 

 sive changes begin in October, and the cells soon become so 

 reduced in quantity as to bring the tubules into contact. 



Rasmussen ('17) found that in the woodchuck (Marmota 

 monax) spermatogenesis is proceeding very slowly during the 

 period of hibernation. The interstitial cells are then smallest 

 in size and probably reduced in number; following upon the 

 renewal of activity in the tubuli contorti, in the spring, the intersti- 

 tial cells undergo a period of rapid development, not, however, 

 attaining their maximum until several weeks after free sperma- 



