26G R. R. HUMPHREY 



The absence of these cells from the sexually immature anhnals 

 I have examined prevents faith in the potency of their influence 

 on development of the secondary sex characters, male sexual 

 organs, etc. If their appearance is delayed until after the first 

 extrusion of spermatozoa, one might well question their influence 

 upon any of the phenomena of sexual maturity. The number 

 of sexually immature animals I have examined is so small, how- 

 ever, that the possibility of an interstitial cell proliferation at 

 some other stage of development has not been absolutely ex- 

 cluded, though conditions under which interstitial cells appear in 

 the adult render such a proliferation in the sexually immature 

 animal improbable. 



That the cells act to regulate growth processess in the germ 

 cells seems improbable. The phenomena of maturation, for 

 example, would occur in Necturus, Cryptobranchus, and Gyrino- 

 philus during their absence. That their disappearance from the 

 testis removed an inhibitory influence, thus permitting matura- 

 tion to proceed, is also improbable, since in Desmognathus they 

 are yet numerous through the entire period in which this occurs, 

 though of course isolated in the caudal shrunken portion of the 

 testis. Champy ('13) inclines strongly to the beUef that the 

 regression of the interstitial cells, i. e., the resorption of their 

 'secretion' products, coincides with the onset of spermato- 

 genesis.*" The persistence of the interstitial cells throughout 

 the entire year in Desmognathus indicates that spermatogenesis 

 may be initiated without the resorption of these elements. In 

 the forms Champy has examined, the spermatozoa are matured 

 in autumn, but retained in the testis until the mating period 

 in the following spring; the interstitial cells, therefore, develop 

 only in the spring and undergo regression immediately preceding 

 the onset of spermatogenesis. In Diemyctylus, which has a fall 

 as well as a spring mating, numerous lobules are emptied in 

 autumn and interstitial cells develop around them. These 

 apparently undergo regression within a sho'rt time after their 

 formation, exactly as they do when developed in the spring. 



'" Champy, in his graphs, fixes the curve of spermatogenesis by the number of 

 spermatocytes I in prophase. 



