228 * R. R. HUMPHREY 



empty and their follicle cells degenerating. The separation of 

 these 'lobes' may be well marked externally, both by intervening 

 constrictions (usually not decided) and color differences. In 

 Diemyctylus one may easily recognize the enlargement containing 

 developing germ cells by its transparent blue-gray color; the 

 lobe containing spermatozoa by its pale yellow color. In 

 Desmognathus there are similar regional differences, but division 

 into lobes is less apparent. The anterior portion of the testis 

 (fig. 6) in which are only primary spermatogonia, is elongated 

 or thread-like, and the caudal shrunken portion, in which lobules 

 are degenerating, is usuall}^ distinguishable because of its reduced 

 size; otherwise there is recognizable no division into lobes. There 

 are, however, in larger Desmognathus males, and in Diemyctylus 

 and Salamandra as well, divisions of the organ which are in 

 structure separate testes, each possessing the differentiation 

 characteristic of the single testis as described above. These 

 divisions, although termed 'lobes' by many investigators, are 

 not to be confused with the lobes previously mentioned. They 

 have been thought of as being of segmental origin. In my opinion 

 they are but the expression of the pattern of growth and degenera- 

 tion peculiar to the testes of those species in which they occur; 

 since this problem is hardly within the scope of this paper, it is 

 reserved for separate and more detailed discussion in another 

 article. 



The caudocephalic progress of a spermatogenetic wave, which 

 results in such distinct lobation in some urodeles, has, because 

 of its comparative rapidity, much less effect upon the form of 

 the testis in Necturus. The caudal portion of the organ en- 

 larges earliest in the season, due to its earlier ripening of sperma- 

 tozoa; it becomes smaller when its spermatozoa are extruded, 

 but prompt regeneration of the lobules brings it back to a condi- 

 tion such that by late winter the testis is of fairly uniform diame- 

 ter, though tending to taper somewhat toward the anterior end 

 and to present a more blunt or rounded aspect caudally. The 

 structure of the organ at different seasons will be discussed in 

 greater detail in connection with the description of changes in 

 the interstitial cells. Sufficient regional differentiation occurs 



