258 R. R. HUMPHREY 



spermatogenesis. Never absent in Desmognathus, they are 

 entirely lacking during the summer months in Diemyctylus, to 

 reappear in the fall, as in Necturus, when degeneration of the 

 emptied lobules begins. 



c. Salamandra atra, Cryptobranchus, etc. Testes of several 

 other urodeles have been examined. Although an account of the 

 interstitial-cell cycle in these must be reserved for a later writing, 

 a brief report of observations on the material already at hand 

 will indicate points of agreement with those urodeles of which 

 more complete studies have been possible. 



The testis of Salamandra atra,^ an European form, shows 

 considerable resemblence to that of Diemyctylus. In larger 

 males it consists of two or three enlargements, which, as in 

 Desmognathus, are in effect separate testes. The constricted 

 regions between these contain primary spermatogonia ranged 

 around the collecting-duct system. Each enlargement or ' testis' 

 in the material examined consists of two portions of approxi- 

 mately equal size, separated by a slight constriction at which 

 degenerated lobules are commonly seen. In front of the ' bound- 

 ary plane' thus established, the 'testis' contains only spermato- 

 gonia; caudal to it, only spermatozoa or lobules recently left 

 empty through their extrusion. 



The cells between lobules of spermatogonia are flattened and 

 without interstitial-cell characteristics. Around the most ce- 

 phalic lobules of spermatozoa they are somewhat thickened and 

 possess distinctly granular cytoplasm. They are far more 

 numerous here as well. The presence of mitotic figures (fig. 23) 

 indicates clearly their manner of increase. Still farther toward 

 the caudal end of the enlargement or 'testis,' around emptied 

 lobules, interstitial cells appear in rings two or more cells in 

 thickness as shown in figure 24. They are now more or less 

 polyhedral in form; their cytoplasm is most dense at one side 

 of the nucleus, where in a centrosphere free from other granules 



8 The material loaned me for this study by Dr. B. F. Kingsbury had been 

 collected in Germany some years previously. It had all been taken in the sum- 

 mer months, at the close of the sexual cycle, but no record of dates of killing 

 had been kept. 



