106 The Spermatogenesis of Desmognathus Fusca 



These begin as hollow vesicles, as Moves has described them in Sala- 

 mandra, in which the wall is composed of the primary spermatogonia in 

 a single row, each enwrapped by one, or possibly two or three follicle 

 cells. By division of the primary spermatogonia, the wall of the vesicle 

 becomes thicker and of several layers of cells, but the descendants of 

 each spermatogonium remain enclosed by its follicle cells and are thus 

 separated into a group or cyst. By increase in size of the cysts, the 

 cavity of the lobule is soon obliterated and the lobule becomes a solid 

 mass of cells. Each secondary spermatogonium of the last generation 

 undergoes a period of growth to form the spermatocyte, nearly doubling 

 in size during the process. Each spermatocyte divides twice to form 

 the spermatids which become transformed into the spermatozoa. As a 

 result of this increase in the number and size of the component cells, 

 the lobule, and therefore the testis as a whole, becomes greatly enlarged. 

 During these changes the cysts are still evident, each encompassed by 

 its follicle cells, the descendants of the cells surrounding the primary 

 spermatogonia. When the spermatids begin their transformation, the 

 cysts — as cysts — become disorganized, and the follicle cells assume a 

 new function, or (probably) the old function is modified to suit the new 

 conditions. The protoplasm increases in amount and is accumulated 

 especially upon one side of the nucleus. In this protoplasm are in- 

 serted the heads of the maturing spermatozoa, as is the case in the organ 

 in the higher vertebrates. AVhen the spermatozoa are fully mature, 

 they lose their relation to the follicle cells and accumulate in the center 

 of the lobule ready for expulsion, while the follicle cells occupy and 

 form the wall of the lobule. The spermatozoa finally pass from the 

 lobule through the short tubule into the collecting duct, and thence 

 by means of the vasa efferentia into the spermatic duct. 



The follicle cells now undergo a degeneration and disappear, so that 

 the lobule, as such, eeases to exist. Each lobule, therefore, has a life 

 cycle of a year; develops, reaches maturity and degenerates, and during 

 this time increases greatly in size, finally to shrink and disappear. 



While the mass of the cells of the lobule undergo the changes of 

 spermatogenesis, a few primary spermatogonia in the apex of the lobule 

 (i. e., near the collecting tubule) remain unchanged and persist through- 

 out the succession of stages through which the other cells pass. When 

 the lobule is greatly distended with the maturing spermatozoa, they 

 become so flattened as to be rocognized with difficulty. After the sper- 

 matozoa have been extruded and the lobule has collapsed, these residual 

 spermatogonia, surrounded by their follicle cells, again round out and 

 present their original appearance and structure. These, by their later 



