A MODIFICATION OF THE URODELE TESTls. 151 



from half to three fourths of the testis contains primary sperm- 

 atocytes. M< ntime, however, in the most caudal lobules these 

 spermatocytes have completed their maturation divisions. 

 Since tli -< too proceed in regular caudocephalic order, it follows 

 that the most caudal portion of the testis finally will contain 

 -permatids. These, in Plethodon males killed in late October or 

 in Xovi -mlier may be found in as much as a fourth of the extent 

 of tin- testis, or, on the other hand, in but a few of its most 

 caudal lobules. The onset of cold weather finally check- the 

 further lonrse of spermatogenesis, and few or no maturation 

 division- then occur until the following sprii 



It is in the fate of those spermatids formed in autumn that \\e 

 find tin < onect explanation of the caudal appendage -ecu in the 

 May or June. For these spennatid-, apparently 

 to transform, undergo degeneration and rc-orption, 

 d;-appeariu:< during the early spring months. The lolmles 

 \\liieh tlii-\ occupied now become very much reduced in size, and 

 the caudal portion of the testis, as a result, assume- the pro; 

 tioi crate appendage of the larger anterior part. In 



thi- appendage, as has been mentioned, an oc 1 -perma- 



toc\ie iii.iv ( !< \elop (.See Fig. 9) and go through it- matnr.i 

 division-; tli is may sometimes result in the belated I'm -ma lion of a 

 \ery -mall n n ml er of spermatozoa. Any extensive development 

 of spt -i mato-onia and spermatocytes in this region, ho\\c\er, is 

 di-la\ed until the time when such a development \\oiild ..fiir in 

 preparation for the next spermatogenetic cy ! . It i> not until 

 late -nnimer or earh' fall, therefore, that the gro\\th pnn - e--e- in 

 tin- appendage, now equivalent to those of the lolmle- anterior to 

 it, obliterate the distinction between the two region-. 



A caudal appendage similar to that in Plethodon glntinosns is 

 found in practically all Gyritwphilus male- killed during the 

 summer months. In this species, ho\\e\er, the greater length 

 .ind reduced diameter of the whole organ (1 i.u- 7.' renders the 

 appendage less conspicuous. Microscopically it- -tructure is 

 coinparaMe to that of the appendage in Plethodon, although it 

 slio\\> an apparently greater effort toward compensatory develop- 

 ment of germ cells. All the reduced lobules contain a small 

 number of primary spermatocytes, or, later in the season, 

 -permatids or spermatozoa. Because of their small number, 



