SEASONAL CHANGES IN INTERSTITIAL CELLS 483 



The great variability in the correspondence between the 

 progressive stages in the sexual cycle and increased intersti- 

 tial cell growth evidently calls for more observations if this 

 line of evidence is to be utilized in the interpretation of the 

 internal secretory function of the interstitial cells of Leydig. 



PRESENT INVESTIGATION 



This report is based upon a study of the testes of thirty-five 

 male woodchucks which have been killed at various times 

 during the past four years. The series includes twenty-three 

 adult animals, one or more years old, some of which have been 

 sacrificed in each month of the year; six younger animals (sev- 

 eral months to nearly one year old), some of which were sexu- 

 ally mature when killed, and six animals which were from about 

 five weeks to several months old. 



Most of the testes were removed before death while the ani- 

 mal was under an anaesthetic (usually ether). Some were 

 removed immediately after death and, in a few cases, several 

 hours after the animal was shot. In the early spring at the 

 critical period of the year when the rutting season commences 

 and when it is difficult to capture the animal alive, a number 

 were shot and brought to the laboratory and the testes taken 

 out. Such material was used as control for that taken from 

 animals kept in captivity in artificial burrows. While both 

 males and females were always together in captivity and while 

 the artificial burrows, as described elsewhere,^ are such that 

 practically normal conditions should prevail, it was found that 

 females kept as late as April were not pregnant. Since they did 

 not breed in captivity, normal controls taken directly from 

 their usual habitat were necessary. Such controls showed, 

 however, that the male sexual cycle was not interrupted, at 

 least as far as the histological picture and the descent and 

 growth of the testis are concerned. 



Except in the first few cases, the gross weight of the animal, 

 the weight of the gastro-intestinal contents and urine and the 



^ Rasmussen, A. T. 1915. Amer. Journ. Physiol., vol. 39, p. 23. 



