SEASONAL CHANGES IN INTERSTITIAL CELLS 503 



The relation of the interstitial cells to the breeding period, 

 when copulation or fertilization takes place, is equally confusing, 

 since this i)eriod of sexual activity (spoken of as rutting in 

 inanj" animals) may occur either when the interstitial cells 

 are showing evidence of increased activity (toad, hedgehog, 

 marmot (?), woodchuck) or when not noticeably changing 

 (frogs, mole). The descent of the testes may occur when the 

 interstitial cells are minimal (mole) or after these cells have 

 commenced to hypertrophy (woodchuck, hedgehog). In the 

 woodchuck they tend to remain scrotal while the interstitial 

 cells are enlarged. Here attention should be called to the ex- 

 periments of Harmes ('13) in which he showed that the character- 

 istic thickening of the skin on the hands of the male frog during 

 the breeding season may be brought about through some in- 

 fluence exerted by Bidder's organ alone in the absence of the 

 testis. This is true even when Bidder's organ has been trans- 

 planted into the dorsal lymph sac, and Bidder's organ contains no 

 interstitial cells. However, the testis alone in the absence of 

 Bidder's organ can also cause this periodic thickening of the 

 skin. 



The general functional reduction which takes place during 

 hibernation also applies variously to the interstitial cells. In 

 most of the hibernating animals they are quiescent during 

 dormancy, but in the toad they are developing. Nor is there 

 necessarily any marked change in their behavior at the onset of 

 torpidity as is also shown in the case of the toad, where they 

 go on increasing, and in the case of the woodchuck, where they 

 remain in the minimal stage to which they have been reduced 

 during the late summer preceding. 



It thus appears that while the periodicity of the inter- 

 stitial cells would suggest some important function for them, it 

 is difficult to say what this function is specifically, because 

 of the lack of uniformity in their behavior. Granting that in 

 the main the ol)servations here discussed are correct, one would 

 hesitate to use them as evidence of any weight in support of the 

 generally accepted idea that the interstitial cells of the testis 

 produce an internal secretion of specific importance to the sexual 

 life of the organism. 



