162 R. R. HrMlMIKKY. 



caudal lobules of this male. Fully mature spermatozoa, of 

 course, would probably be even less susceptible than those in 

 transformation. Their survival of the winter in the testes of 

 numerous Urodeles (Diemyctylus , Nectums, Ambystoma, etc.) 

 would bear out this hypothesis. 



Unusual types of appendage, such as the two above discussed, 

 further indicate that the similar structure found under usual or 

 normal conditions is but a result of the action of environmental 

 factors upon the spermatogenetic processes. The caudal 

 appendage of such general occurrence is no indication of a 

 functional reduction of the testis in phylogeny or ontogeny, nor 

 does it represent a structural adaptation for a changed function, 

 as do sterile portions of the gonads in certain Teleosts. Its 

 occurrence is limited to testes of a simple type, in which the 

 germ-cell stages occur in caudo-cephalic succession, and cells of 

 any one region are all in approximately the same stage of develop- 

 ment. Under such conditions, germ-cell degeneration limited 

 to cells of a particular type readily affects the form of the testis in 

 a particular limited region. In a testis in which every tubule 

 contains cells of numerous types (as in anuran, reptile, bird, 

 mammal) such modifications of the organ are of course impossible. 



SUMMARY. 



1 . The testes of several species of Urodeles frequently possess a 

 slender caudal extension or appendage suggestive of a functional 

 reduction of the organ. 



2. This caudal appendage is present only during the summer 

 months. It disappears in autumn, to reappear in the following 

 spring. 



3. Study of its cyclic changes indicates that its appearance is 

 clue to degeneration of the germ cells of the more caudal lobules 

 of the testis. 



4. The germ-cell degeneration is interpreted as resulting from 

 the unfavorable conditions of winter; the cells most advanced in 

 development are apparently the most susceptible and they alone 

 degenerate. 



5. The caudo-cephalic order of development of the germ cells 

 results in the localization of the most advanced stages in the 

 caudal end of the testis; their degeneration reduces this region to 

 a slender caudal appendage. 



