150 R. R. HUMPIIRKY. 



wave; Kingsbury, '02; Humphrey, '21, '22), the caudal region 

 or appendage would be expected to contain at this time, in 

 addition to its residual primary spermatogonia, only cells further 

 advanced in development than those of the region anterior to it. 

 That is, we should expect to find here only numerous spermatids 

 undergoing transformation, rather than the several sparsely- 

 represented cell types actually encountered. 



Later in the season (July, August) it will be found that some of 

 the spermatids in the appendage may have undergone transfor- 

 mation; a very small number of spermatozoa may eventually 

 mature and leave the lobule. This number is as a rule negligible. 

 The slow increase of secondary spermatogonia is the most 

 important change in the lobule of the appendage during the 

 summer; these arise by proliferation of the residual primary 

 spermatogonia of the lobule apex. Such primary spermatogonia 

 always are to be found in the appendage, though all other germ 

 cell stages be absent. The appendage is therefore not a sterile 

 region of the gonad, as is the caudal portion of the testis of 

 certain Teleosts. Germ cells are never entirely lacking. 



After the extrusion of the spermatozoa from the testis proper, 

 a prompt regeneration of its emptied lobules is accomplished 

 through the rapid multiplication of their apical spermatogonia. 

 This, indeed, begins some time before the lobules are actually 

 emptied. The development of spermatogonia in the lobules of 

 the caudal appendage now keeps pace with or, to be exact, 

 precedes their development in the lobules directly anterior to it. 

 The enlargement of its lobules, of course, explains the disap- 

 pearance of the appendage as such in animals examined in 

 autumn, the division of the testis into two regions becoming more 

 and more completely obliterated, as lobules throughout the 

 testis become uniformly filled with secondary spermatogonia. 



The spermatogonia of the regenerated lobules now begin to 

 undergo the characteristic transformation by which they become 

 spermatocytes of the first order. The latter then enter upon 

 their growth period. Following the rule of progressive caudo- 

 cephalic development, the formation of spermatocytes first 

 occurs in the most caudal lobules, formerly the territory of the 

 appendage. Lobules successively farther and farther cephalad 

 proceed in development after the same manner, until in October 



