SEASONAL CHANGES IN INTERSTITIAL CELLS 493 



of cells from serial sections of the testes at th? various periods 

 of the year would, of course, be necessary to rule out individual 

 variations and to definitely prove that there is an increase 

 in the number of cells and what that increase in number 

 amounts to. The facts cited above, however, make it very 

 probable that in the adult woodchuck there is a considerable 

 increase also in the number of interstitial cells after waking 

 up from hibernation although there is no direct evidence of either 

 mitosis of or amitosis. 



The pigment cells do not undergo any growth or increase in 

 number. On the contrary they appear very inert and gradually 

 decrease in prominence. 



Going hand in hand with this interstitial cell hypertrophy, 

 there is still further increase in the size of the testis and a re- 

 newed activity in the tubules. The spermatocytes rapidly 

 change to spermatids and free spermatozoa are seen by the 

 last of March. The most active stage (when most spermatozoa 

 appear to be set free) in the spermatogenic process is reached 

 early in April, by which time the testes have descended into 

 sessile scrotal pouches beside the penis. Thus the renewed 

 activity in the testis anticipated by Gushing and Goetsch ('15) 

 actually takes place; but their assumption that this might be 

 attributed to the influence of the functionally reactivated pars 

 anterior of the pituitary body, does not necessarily follow, 

 since there is nothing to show that the testes or other organs 

 of the body — all of which show this renewed activity upon 

 awakening of the animal from hibernation — are influenced 

 through the pituitary rather than that the pituitary in common 

 with the other organs is influenced by the factors responsible 

 for the general awakening; that is, the pituitary and the testes 

 may have been influenced by the same factors rather than the 

 latter by the former. Furthermore, it is not even certain that 

 the pituitary does always undergo the change reported by these' 

 authors and by Gemeli, for Mann ('16) found that in the thir- 

 teen-lined groundsquirrel such changes while occurring in some 

 animals did not in others, although the testis underwent a sea- 

 sonal change. Jackson ('17) thinks it highly probable that 



