154 R - R - HUMPHREY. 



probable mode of development of the appendage in Eurycea. 

 These lobules contain numerous karyolytic cells, particularly in 

 their peripheral portions. In the most caudal lobules, a syn- 

 cytium of Sertoli cells, with cell debris and fat droplets in its 

 meshes, indicates the region of earliest degeneration; here the 

 lobules are already greatly reduced in size. More anteriorly 

 fewer degenerations have been completed and the earlier stages 

 of nuclear breakdown are readily observed. Here the lobules are 

 as yet but little reduced in size. An appendage of the testis is 

 therefore not sharply marked off at this time, the entire posterior 

 third of the testis having the form of a short cone. 



The germ cells appear to begin degeneration immediately after 

 synizesis, or possibly to degenerate without recovery from this 

 condition. They are stricken, therefore, at the very beginning 

 of the spermatocyte growth period, rather than after it has well 

 started, as in Gyrinophilus. 



It is worthy of note that the proliferation of spermatogonia to 

 replace degenerated germ cells seems to begin early in May. 

 Since a similar proliferation of spermatogonia is taking place at 

 this same time in the more anterior lobules of the testis, it follows 

 that the appendage, later in the year, will correspond in develop- 

 ment with the more anterior rather than the posterior portion of 

 the organ. 



The appendage of the testis in Plethodon cinerius is well 

 developed in but relatively few males. Frequently it includes 

 only two or three caudal lobules; in such cases it would of cour.e 

 be passed over unobserved in gross examination. The structural 

 features of such lobules, however, warrant classing them with the 

 well-developed appendages of other males. 



The development of the appendage may be briefly outlined. 

 In males killed in November or December there has been as yet 

 no development of spermatocytes or spermatids. Yet in animals 

 killed as early as March a caudal appendage may be present. At 

 this time its anterior lobules show karyolytic cells; in the body of 

 the testis immediately adjacent (or even in the same lobule or the 

 same cyst with degenerating cells) are spermatogonia of the last 

 generation, ready to transform into spermatocytes. The germ 

 cells therefore appear to be stricken and degenerate during that 

 critical period of transition from spermatogonium to sperma- 



