478 ANDREW T. RASMUSSEN 



cept within their own bodies, and hence are deprived of food, in 

 the ordinary sense, for about four months out of each year. 

 This may thus be considered a long period of physiological in- 

 anition. During much of this time they are very dormant and 

 have the usual low body temperature (a few degrees above 

 0°C.), slow circulation and respiration, etc., characteristic of 

 hibernation. 



HISTORICAL 



While the interstitial cells were discovered in 1850 by Leydig, 

 the first report on changes in these cells either in connection 

 with the seasons of the year or with the sexual cycle of the 

 adult, did not appear till many years later when Hansemann 

 ('95) reported that he had observed the testis of the marmot 

 and found that the testis of the hibernating animal, in which 

 there is no spermatogenesis, contains practically no inter- 

 stitial cells, there being only a few spindle-shaped cells be- 

 tween the tubules. After the animal has been awake for two 

 months, however, and spermatogenesis is going on, the inter- 

 stitial cells are very numerous, so much so that they give the 

 appearance of a sarcoma. He considered that these cells prob- 

 ably constitute an organ with some specific function. 



Friedmann ('98) followed with an extensive study of the 

 more or less parallel development of the interstitial tissue and 

 the progress of the spermatogenic cycle in frogs (Rana fusca, 

 Rana viridis, Hyla arborea) and the toad (Bufo vulgaris). In 

 frogs he found an increase in the interstitial cells during the 

 progress of spermatogenesis as autumn approaches. Beginning 

 with the end of October with the cessation of spermatogenesis, 

 the interstitial cells almost disappear and remain minimal till 

 about' May. An important point mentioned by Friedmann in 

 connection with Rana viridis is the observation that in the same 

 testis there may be a difference in the amount of interstitial 

 tissue. Where the spermatogenic process is most active, there 

 the interstitial cells are most developed. In the tree frog (Hyla 

 arborea) the interstitial cells seem to be about a month behind 

 in development in comparison with the brown and the green 

 frog. 



