SEASONAL MODIFICATIONS IN TESTES OF VERTEBRATES 



Z65 



considerably enlarged. Active sperma- 

 togenesis is found in April, and free 

 spermatozoa are present in the genital 

 passages at the end of the month. Sper- 

 matogenesis continues until September, 

 and from then on the testes decrease in 

 size. According to this investigator the 

 quantity of interstitial cells runs parallel 

 with spermatogenesis. The increase in 

 size of the testis, he says (z6, p. Z53) is due 

 partly to the increase in the size and num- 

 ber of seminiferous tubules, but even more 



matogenesis. Part of the intertubular 

 increase is due to the increase in the 

 vascular bed, as Marshall has observed, 

 but part appears to be due to interstitial 

 cell increase. A study of the Hedgehog 

 alone might lead one to infer that the 

 interstitial hypertrophy paralleling sper- 

 matogenesis and sex activity had some- 

 thing to do with the increased sex activity 

 of that period. Such an inference is not 

 justified because this parallelism is not 

 found in other species. Tandler and 



JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. 



TALPA EUROPEA - OUm VE 



-QUANTITY OF .SPERMATIC TTS5UE, QUANTITY OF INTERSTITIAL TI5SU£ 



JAN. FEB. MAR. APR. MAY JUNE JULY AUG. 5EPT. OCT NOV. DEC 



CHAKnZDI ERINACEUS EUROPEUS 

 - QUANTITY OF SPERMATIC TISSUE, QUANTITY OF INTERSTITIAL TISSUE 



to proliferation of interstitial cells. This 

 results in wide separation of the tubules. 

 Blood vessels of considerable size are not 

 uncommon, but they disappear when 

 retrogression sets in. Rasmussen states 

 that there is an actual increase in the 

 number of interstitial cells during part of 

 the spermatogenic wave in marmots, 

 which his chart shows reaches its maxi- 

 mum after mating. Spermatogenesis 

 continues during the summer in the Hedge- 

 hog, and in this species the interstitial 

 cell hypertrophy therefore parallels sper- 



Grosz found that in the mole the only 

 parallelism present is between spermato- 

 genesis and sex activity. This parallelism 

 is constant in all mammals. The quantity 

 of interstitial cells in moles is at a mini- 

 mum during sex activity, and in marmots 

 they reach a maximum only after birth of 

 young. This is long after mating has 

 ceased. To function as activators of sex 

 activity the interstitial cells should de- 

 velop prior to or at the same time as 

 spermatogenesis. As a matter of fact 

 their increase follows sex activity. 



