66 R- R- HUMPHREY. 



(a) The portion of the testis emptied in autumn is not regen- 

 erated immediately, since the residual spermatogonia remaining in 

 the region do not begin division, but remain quiescent for several 

 months. 



(b) The functional testis in the next season develops anterior 

 to the emptied region, from a part of the original germ-cell cord 

 not developing spermatozoa in the first season. 



(c) When the emptied lobules degenerate and disappear, the 

 region they occupied remains as a slender strand or cord of 

 residual spermatogonia. 



(d) Spermatogonia in the caudal end of the cord finally begin 

 division. Lobules of germ cells develop and a caudal " secondary 

 testis " or lobe is formed. 



(c) The second lobe shifts forward each season in the same 

 manner as does the first. From the germ-cell cord left in its wake 

 a third lobe eventually arises. The process is repeated in the case 

 of other lobes subsequently added. 



(/) The most anterior lobe finally reaches the cephalic end of 

 the germ-cell cord and disappears. Other lobes follow in due time, 

 but are replaced by new ones originating caudally. 



4. New lobes have been found to appear in no other manner 

 than by the process above outlined. 



(a) Sexually immature males never show numerous growth 

 centers in the germ-cell cord. 



(&) New lobes do not arise by the promiscuous establishment 

 of secondary growth centers between lobes already present. 



(c) Small anterior lobes always prove to be disappearing or 

 " running out " ; new lobes have not been found to develop in this 

 region. 



5. The conditions necessary for the formation of a multiple 

 testis are : 



(a) A slow forward movement of the spermatogenetic wave. 



(b) Delayed regeneration of the emptied lobules. 



(c) The lapse of a time interval following which the long- 

 postponed regeneration brings into existence the new lobe. The 

 unregenerated region between lobes is that commonly termed 

 " sterile." 



