156 R. R. HUMPHREY. 



condition obtains. Lobule regeneration proceeds without delay, 

 beginning even before the spermatozoa have left the testis. The 

 spermatogonia of the caudal lobules may even transform to 

 spermatocytes, and these complete their growth and maturation 

 periods, within a few weeks after emptying of the lobules begins. 

 It is this precocity of development, in fact, which results in the 

 formation of a caudal appendage, since cells reaching a certain 

 stage during the fall and winter are fated to degenerate. Though 

 this reduces in size the caudal region of the testis which these 

 germ cells occupied, such reduction is never so extreme as is that 

 of the emptied testis of Desmognathus, nor is its regeneration so 

 long delayed. The appendage of Plethodon, for example, is 

 always restored to the normal diameter of the testis by the 

 proliferation during the summer of spermatogonia for the next 

 sexual cycle; the emptied region in Desmognatlms does not begin 

 regeneration for several months longer, and even then, at first, 

 only at its caudal extremity. A part of the emptied region in 

 Desmognathus or Diemyctyhis thus comes to be a slender inter- 

 mediate cord joining two lobes of a multiple testis. The ap- 

 pendage of Plethodon, on the other hand, is annually restored to 

 the normal diameter of the testis proper, and a multiple testis in 

 this species is unknown. 



From the preceding outline of its origin and fate in different 

 species, the variations in length and diameter of the true ap- 

 pendage should be easily understood. Its length depends upon 

 the number of caudal lobules in which germ cell degeneration has 

 occurred; its diameter varies with the degree to which the 

 products of degeneration have been resorbed, or the extent of the 

 restoration of its germ cells by proliferation of the residual 

 spermatogonia. Its occasional complete absence in summer 

 months indicates that none of the usual degeneration has occurred 

 in the preceding seasons; its constant absence in fall and winter 

 months is due to the annual development of spermatogonia, a 

 process which is common to both the appendage and the testis 

 proper. This obliterates the striu cural differences between the 

 two regions, leaving them alike save for the slightly more ad- 

 vanced condition of the germ cells in the territory of the ap- 

 pendage. 



In addition to its variations as between species and between 



