SEASONAL CHANGES IN INTERSTITIAL CELLS 477 



velopment of the interstitial cells at different periods of life 

 and the periodic changes which they undergo in adult animals 

 as related to the sexual cycle. This last line of evidence is 

 somewhat conflicting. It is, of course, difficult in most of 

 the higher animals, epecially domesticated ones, to correlate 

 the various phases of the spermatogenic cycle with changes 

 in the interstitial cells because the various progressive and 

 regressive changes in the tubuli contorti are going on more or 

 less side by side at the same time. For this reason Tandler 

 and Grosz ('11) selected as material for a study of this question 

 an animal (mole) in which the interval between rutting periods 

 was sufficiently great to separate the stages in the spermatogenic 

 cycle, since this animal is sexually active only in the spring. 

 The woodchuck, which is abundant in many parts of the United 

 States and Canada and even Alaska (Howell, '15), similarly 

 should furnish facts of interest in this connection. This ani- 

 mal also is sexually active only in the spring. The female gives 

 birth to but one litter a year, the young being born about the 

 last part of April or the first of IVIay, according to Merriam('84) . 

 These dates agree well with the general life history of these 

 animals as observed in this vicinit}^ Merriam further states 

 that along the western border of the Adirondacks they go into 

 hibernation late in September and remain till the middle or 

 last of March. In this region in their normal habitat they do 

 not retire till nearly a month later, and those kept in captivity 

 usually remain awake till the last of November. Probably those 

 that retire in natural burrows do not become actually dormant 

 till several weeks afterwards. 



Incidentally the study reported here is of interest also in con- 

 nection with the subject of histological changes during inani-' 

 tion — a subject having many important bearings upo'n growth,^ 

 metabolism and physiological adaptation. All species of Ameri- 

 can marmots hibernate profoundly. They store up no food, ex- 



2 This point is especially discussed by Sergius Morgulis, Arch. f. Entw. d. 

 Organ., 1911, vol. 32, p. 169. Here is also reviewed the literature on the effect 

 of experimental inanition on histological changes in the testis. This deals, 

 however, with spermatogenesis and liot with the interstitial cells. The data 

 reported in this connection does not show very uniform results. 



