INTERSTITIAL CELLS OF URODELE TESTIS 217 



tozoa have appeared, and then persisting in this greatly developed 

 condition fully two months after the spermatogenetic cycle has 

 ended. 



It would appear from the above-cited results that considerable 

 variation occurs in the relations between interstitial cell growth 

 and spermatogenesis in the testes of mammals: the two may 

 appear directly correlated, as in the marmot and hedgehog; 

 regressive changes in the germinal tissue may be accompanied 

 by the maximal development of the interstitial tissue, as in the 

 mole; or interstitial cell development may follow rather closely 

 after the period of greatest activity in the tubuli contorti, as in 

 the w^oodchuck. Regarding this variation, Rasmussen says: 

 ''This seems to be the most striking correlation, namely, that 

 the interstitial cells follow with renewed growth somewhat 

 behind the spermatogenetic cycle. ' ' He considers it possible^ 

 in this connection, that in the mole they ''are only somewhat 

 more than usually behind." 



The same lack of uniformity is found in any of the higher 

 vertebrate classes of which enough members have been studied 

 to render comparisons possible. 



Very little has been done among birds. The only complete 

 study of a member of this class was made by Stieve ('19), who 

 worked on the testis of the corvus, an European bird of the raven 

 type. He found that the interstitial tissue appeared more 

 prominent in the testis in the months following the breeding 

 period, when the tubules had become relatively shrunken; but 

 he concluded that there was no actual increase in the bulk of the 

 interstitial cells at this period. 



No observations on the seasonal changes in reptiles have been 

 encountered save the statement of Mazetti ('11) that interstitial 

 cells were abundant in the testes of hibernating snakes. 



Several investigators have published accounts of the cyclic 

 changes in the testes of anurans. Friedmann ('98) found the 

 development of interstitial cells running parallel with the progress 

 of spermatogenesis in the frogs (Rana fusca, Rana viridis, Hyla 

 arborea) and the toad (Bufo vulgaris). When spermatogenesis 

 has practically ceased, the interstitial cells tend to become re- 



THE AMERICAN JOURNAL OP ANATOMY, VOL. 29, NO. 2 



