230 R. R. HUMPHREY 



The period of growth follows; maturation divisions occur in 

 July and August, and in the latter month transforming sperma- 

 tids are present in the caudal lobules. By October spermatozoa 

 are mature throughout the testis; animals killed late in the month 

 showed the greater portion of the testis empty and the caudal 

 lobules well advanced in degenerative changes, while the sperma- 

 togonia were growing to produce the lobules of the next sexual 

 cycle. The mating period presumably occurs in the autumn at 

 the close of the spermatogenetic cycle, since it is at that time 

 that the greater part of the spermatozoa are extruded from the 

 testis. The spermatozoa present in the spermathecas of the 

 female in the fall and winter months (Kingsbury, '95) are doubt- 

 less acquired in autumn rather than held over from a spring 

 mating, if such should occur. 



Interstitial cell cycle in Necturus 



a. Absence of such cells in summer months. During July and 

 August one finds throughout the testis the spermatocytes in 

 various growth and maturation stages, with transforming sperma- 

 tids in a few caudal lobules of the testis perhaps before the end 

 of the last-named month. The testis, during these months and 

 in September, is at the greatest size it attains at any time in 

 the sexual cycle. The increase is in the diameter more than in 

 the length of the organ. The individual lobules retain their 

 customary fan-shaped arrangement about the superficial longi- 

 tudinal collecting duct; each lobule extends from the hilus, in 

 which this duct lies, to the periphery of the testis. The lobules, 

 by their increased length, have brought about the increase in 

 diameter so noticeable at this period, and though each elongated 

 lobule will now contain germ cells in some one of the late stages 

 of spermatogenesis, in the centrally located apex of each lobule, 

 as shown in figure 3, will be found the primary. and even some 

 secondary spermatogonia from which later will develop the 

 regenerated lobule of the next sexual cycle. The elongated 

 lobules during this period are greatly distended, so that they come 

 to press closely one upon the other; their shape is modified 



