A MODIFICATION OF THE URODELE TESTIS. 157 



individuals of the same species, the appendage undoubtedly 

 varies in length in the same individual in -ucre--ive year- d its 

 adult lift-. Environmental conditions differ from year t year; 

 this variation i- likely to be reflected in the spermatogenetic 

 pr<> It', for example, the climatic condition- of autumn 



r.il.lr for tin- maturation divisions of the spermat<u \ te- in 

 gliitinosus) are continued long beyond their u-u.il 

 I. .1 . r portion of the testis is filled with -penn.itid-. 



It. on tin other li.uid, these maturation division- 'lerked by 



tin- unu-n.illy early onset of cold weather, fewer caudal lobules 

 will be^in the winter containing spermatids. In the form< 

 the appendage \\ill be longer, and in the latter . horter, 



\\lien the 'ration of these spermatids has been completed. 



In -OHM- .mini.ils, of course, few or no germ cells may rearh the 

 <ritual period of development in the fall month-; in this, 

 probably, lies the explanation of the absence of an append.!. 

 .1 londition frequent in Eurycea and Plethodon cin, -liMUiJi 



tins and Plethodon glntinosus. In aid 



Cryptobranchus a caudal appendage never develops; . n.il 



d generation of germ cells, of it occurs in these spe ies, i- either 

 np| limiied to one region of the testis or is not sultn -irmly marked 

 to < aii-e a noticeable reduction in its size. 



I Je^eiiera lion of germ cells in the Urodele te-ii- was eail\ 



de--ribed by Flemming ('87) in Salatnandra. The>e cell>, it 



appeal-, \\tie secondaiA' spermatogonia. From the .K--< \\\>i 



i >t l-'lemming it \\ < mid seem that they were not definitely 1< < ali/ed 



in the -perm cycle or limited to a defmitt in the 



;-. Heim.nr 38) describes these same degenerations in 



iti detail; neither he nor Flemming advance si <>ns as 



ti then caua ^nilicance. F)rtiner ('94) later attempted to 



dein.in-tiate that these degenerations were caused b\ the action 



oi a para-ite upon the germ-cell nucleus. 



The work of Kingsbury and Hirsh ('12) first railed attention to 

 the o'vnnence of such degenerations at a delinite point in the 

 -permati'v,enetir cycle of Desmognathns. In this 1 rudde. the 

 mlar\ spermatogonia of the "last generation" in e.u h >e\ual 

 ( \< le are a | >| . : i en t ly unable to complete their transformation to 

 :-pennator\ te- and begin the usual sperm.itoryte ^r>\\ih period. 

 In-tead. the\- undergo degeneration and ultimateK di-ap[ 



