A MODIFICATION OF THE URODELE TESTI-. 155 



toc> In sucli a period, also, occur the degenerationsdescribed 



\>y Kingsbury and Hirsh ('12) in Desntognathns. These, however, 

 take place at the end of the spermatogenetic cycle, checking the 

 further development of primary spermatocytes for the season, 

 while the - : ations just described in Plethodon cincriits occur 



at the beginning of the cycle and delay the development of 

 spermatocytes until a later (and presumably more favorable) 

 period. \\\ May I lie caudal portion of the testis pr- mains 



normal VM-.-A ii rmatocytes, while traces of degenerating cells 



in the appendage have practically or entirely di- :ed. 



1 hiring il inder of the summer the lobules of the appeix 



contain only a limited number of spermatogonia. 'I 

 i" In- no 'tii|H n-.itory development of sperma 1 3 in 



J''.uryifn or (lyrinof-hilus, so that no germ cells at all are matured 

 in the append. i.e. In this respect Plethodon cincrins i- -imilar to 

 '<:nil,n> i'Ju.'inosus, in which few if any germ evil- c'me to 

 maturity in the appendage. Its spermatogonia prlife; 

 during; the -nmmer and early fall. Their increase in number, and 

 the e\ mi-ion of the spermatozoa from the body of th< . at 



length obliterate the si/e difference between the t\\o n-i"n-, as in 

 the MI her -pe. ies considered. 



The appendage of the testis in Plethodon and other I rodeli 



b(.\e de-t ribed, is clearly different, both in origin and late, 

 lYi'in the re. lured caudal portion of the u--t:- i in 

 /'< \-i:<'i[nnthits and Dicmyctylus. The latter stnicture. in adult 

 male-, arises by the emptying of the entire region producing 

 spermatozo L. 1'his, of course, occurs at the end of the .-perma- 



iie tii- 1 M le. The emptied lobules are not at once restored by 

 pri'liU-ration < .f their residual priman," spermatogonia, which in 

 the-e species may remain quiescent for several months. The 

 re-ul t i- the reduction of the emptied portion of the testis to a 

 -lender cord. Regeneration of the lobules finally taking place at 

 the randal end of this cord, an enlargement arises at that point, 

 -epar.iteil from the testis ahead of it by a -lender intervening 



Hi in which lobule regeneration has not yet occum- .6). 



In tin- manner ari-e- the so-called lobed or multiple te-tis of 

 l\^nwgnathus and Diemyctylus (Humphre>-. '22). A neces- 

 -arv condition for ii- appearance is delayed lobule regeneration. 

 In the -pei-ie- pD--e--ing an appendage, quite the i> i this 



