SEASONAL MODIFICATIONS IN TESTES OF VERTEBRATES 



2.61 



ing the winter. In the spring and early 

 summer division and growth of germ cells 

 take place. By October spermatozoa are 

 mature, and at the end of that month the 

 greater portion of the testis is again empty. 

 The testis during July, August, and Sep- 

 tember is at the greatest size it attains at 

 any time. The lobules are then enlarged 

 and angular rather than circular, with 

 blood vessels occupying the spaces where 

 three or more tubules meet. No cells 

 recognizable as interstitial cells can be 

 found at this time. In late October the 

 interstitial cells are developed from stro- 

 mal cells, a process beginning in the 

 caudal portion of the testis following de- 

 parture of mature spermatozoa. Accord- 

 ing to Humphrey their development is to 

 be looked upon as correlated with the 

 regressive phase of spermatogenesis and 

 not as a seasonal condition. The develop- 

 ment of interstitial cells normally occurs 

 following emptying of the lobule. 



What has been given above for Necturus 

 is true in general for Cryptobranchus, 

 Pkthodon, Diemyctylus, Splerepes, Gyrinopbi- 

 lus, and Desmognathns. Moreover, in 

 some of these species interstitial cells 

 completely disappear while, and even 

 before, spermatogenesis proceeds. 



Chart V, built from data offered in 

 Humphrey's papers, shows clearly, as 

 stated by that author, that interstitial 

 cell development follows degeneration 

 within the lobule and that it is not a sea- 

 sonal condition. He offers much data 

 clearly analyzed in support of his con- 

 clusions. This chart shows that the 

 breeding season must be carefully noted, 

 for in this species the interstitial cells are 

 abundant during spring, when most species 

 breed, but are at a minimum during 

 October, its true breeding season. In a 

 recent communication Humphrey states 

 that he "is not sure that the breeding 

 period has been clearly established. 



Animals have sperm in their vasa defer- 

 entia for some time after the testis empties. 

 Necturus males are capable of mating in 

 spring as well as in the fall. This is also 

 true of Pletbodon, Diemyctylus, Spelerpes, 

 and other urodeles. The mating season 

 may extend over several months . ' ' 



Aron (3, p. Z5) stated that of the divers 

 elements of the testis only the glandular 

 tissue parallels the seasonal evolution of 

 sex characters. This glandular tissue 

 develops by multiplication of Sertoli cells 

 within a cyst (lobule of other authors). 

 The connective tissue cells of the cyst wall 

 also increase. The cyst gradually comes 

 to appear like a corpus luteum. Its walls 

 soon disappear, the cells rapidly atrophy, 

 and a cicatricial tissue with globules of 

 fat is substituted. The formation of this 

 gland as observed by Aron differs some- 

 what from that reported by Champy, but 

 they both refer to this body as having an 

 endocrine function. Aron states (3, p. 

 116) that when the sex characters are 

 present the gland is present and that when 

 the gland is present the sex characters are 

 present. This might well be a coinci- 

 dental affair, but in Aron's hands experi- 

 mental evidence appears to give it some 

 significance. When he has cauterized this 

 tissue without injury to the remainder of 

 the testis the secondary sexual characters 

 disappear. When the remainder of the 

 testis is removed without injury to this 

 organ the secondary sex characters pursue 

 the normal course. However, the evi- 

 dence is not conclusive because (1) it is 

 almost impossible to cauterize this portion 

 of the testis without injuring the blood 

 supply to the remainder of the testis and 

 (z) the change resulting from cauteriza- 

 tion of this tissue is only a slight speeding 

 up of the disappearance of characters that 

 are soon to disappear as a normal process. 

 Humphrey has also called my attention to 

 the fact that in cauterizing this tissue the 



