158 R. R. HUMPHREY. 



The polarity of the testis in Desmognathus, and the cephalo-caudal 

 seriation of its germ cell stages results in the localization of the 

 degenerating cells in a "zone" near the anterior end of the organ. 

 Cephalad of this, as a "boundary plane," according to Kingsbury 

 and Hirsh, the spermatogenetic processes now lag, no more 

 spermatocytes developing until at the beginning of the next 

 cycle. The degenerations, it is therefore suggested, bear some 

 relation to a regulation of the spermatogenetic processes. 



To the writer's knowledge no detailed study of boundary plane 

 degenerations in other Urodeles has ever been reported. The 

 occurrence in Diemyctylus of a "boundary plane" comparable 

 to that of Desmognathus was noted briefly in a previous paper 

 (Humphrey, '21). The degeneration of spermatogonia in these 

 two species occurs at the same point in the sexual cycle and is 

 limited to a corresponding region of the testis. Similar degenera- 

 tions would doubtless occur at a comparable time and place in 

 any Urodele showing the same general plan of spermatogenetic 

 pattern (i.e., slow spermatogenetic wave, with delayed lobule 

 regeneration features resulting in a multiple testis). Sperma- 

 togonial degenerations unquestionably occur in Urodeles with a 

 different pattern of spermatogenesis, but in these they are not so 

 definitely localized in the testis and do not affect entire lobules; 

 hence no well-marked "plane" is established. 



Though "boundary plane" and other spermatogonial degenera- 

 tions are possibly associated with a regulation of the sperma- 

 togenetic process, it seems unlikely that the degenerations 

 described in this paper have any such significance. They occur 

 at the opposite end of the testis, and so to speak at the 

 opposite end of the spermatogenetic cycle. The cells that 

 suffer degeneration are not the last generation of a season's 

 output, but the first. They in each case are most advanced in 

 development of any cells in the testis at the time. They are 

 precociously developed in some cases several months ahead of 

 the similar cells privileged to go on to complete maturity. 

 Spermatids formed in May in Pletlwdon glutinosus, for example, 

 transform into functional spermatozoa, but spermatids developed 

 in the preceding November usually undergo degeneration before 

 spring. Winter, in this case, comes on after the beginning of a 

 new spermatogenetic cycle; certain cells apparently h;i\ i- ivarlu-d 



