INTERSTITIAL CELLS OF URODELE TESTIS 225 



lobules, from the main collecting duct. This type of testis is 

 seen in Salamandra atra and Diemyctylus; it is due to the elon- 

 gation of the duct branches referred to above that the organ 

 assumes the more rounded form seen in these urodeles; in Die- 

 myctylus, in particular, the transverse diameter of the testis may 

 at times be nearly equal to its length. 



Between the three types of structure recognized by Spengel 

 there may be transitional forms. Kingsbury ('02) describes the 

 testis of Desmognathus as being a combination of two of these 

 types, the longitudinal collecting duct, central in position through 

 most of its extent becoming peripheral toward the ends of the 

 organ. In passing, it might be mentioned that Hoffman (78) 

 suggests the homology of this central duct and its branch tubules 

 with the rete testis and vasa recta of higher vertebrates. 



Though differing in their arrangement and relation to the 

 collecting duct, the lobules in the testis of all urodeles are funda- 

 mentally the same. They are the structural units of the testis. 

 Each, as has been noted, is connected to the central collecting 

 duct, or to one of its larger branches, by a short tubule. Each 

 is separated from its neighboring lobules by an investment of 

 connective tissue, which is much less apparent when the lobules 

 are in their most distended condition. The development of the 

 lobule, as described by Meves ('96) in Salamandra, McGregor 

 ('99) in Amphiuma, and Kingsbury ('02) in Desmognathus, 

 applies, in general, to the lobule of all urodele testes observed in 

 this study. It begins as a group or vesicle of large primarj^ sper- 

 matogonia at the end of a cord of cells representing the branch 

 tubule. (The term 'cord' is used because the lumen may not 

 always be evident.) Each primary spermatogonium (fig. 1) has 

 surrounding it one to several cells of epithelial type, forming a 

 'follicle.'^ By increase in number these spermatogonia form a 

 hollow vesicle — the young lobule (fig. 2) ; the walls of this lob- 

 ule later become made up of groups or cysts of cells, each group 

 representing the product of several divisions of one of the early 



® The follicle cells of the urodele testis are similar in function to the Sertoli 

 cells of the mammal, and will be referred to frequently in this paper as Sertoli 

 cells. 



