52 R. R. HUMPHREY. 



In developing males of either Desmognathus or Plethodon, the 

 testis, subsequent to the establishment of the urino-genital connec- 

 tion, consists of but a slender cord of primary spermatogonia much 

 as in Fig. i, along whose entire length extends the longitudinal 

 collecting duct. So far the testes of the two animals are sub- 

 stantially alike. Neither shows any indication of the establishment 

 of growth centers such as might result in the formation of a many- 

 lobed organ. Preceding the onset of sexual maturity the sperma- 

 togonia of the caudal end of the germ cell cord begin division, and 

 eventually fully developed lobules are formed. This development, 

 of course, proceeds caudocephalically in both animals. In Pletho- 

 don, whose wave rate is the more rapid, lobules are developed and 

 spermatozoa are matured, in the male's first year of sexual ma- 

 turity, throughout a considerable part of the length of the original 

 germ cell cord. In DesinognatJius, because of the slower wave 

 rate, spermatogenesis is checked after proceeding but a fraction of 

 the length of the gonad. A boundary plane is established in the 

 manner previously mentioned, and spermatozoa are matured only 

 caudal to its location. 



At the time of maturity of the first spermatozoa, then, the testes 

 of the two animals agree in consisting of but one lobe each. That 

 of Plethodon is represented diagrammatically by Fig. 24 of Chart 

 I., in which the unshaded area represents the part maturing sperm- 

 atozoa. The testis of the young DesrnognatJnts male is represented 

 by Fig. i, in which the same scheme of shading is employed. The 

 boundary plane is indicated by the line b. The smaller fraction of 

 the testis becoming functional in Desmognathus is to be noted. 



Following the extrusion of the spermatozoa, in Plctliodon, lobule 

 regeneration proceeds rapidly. (It begins, indeed, considerably 

 before the spermatozoa leave the lobule.) Though the form of 

 the organ, before all of the more anterior lobules have been emptied 

 and regenerated, will appear as in Fig. 25, prompt regeneration of 

 the lobules during the winter the spermatozoa being extruded in 

 autumn brings the testis, by spring, back to the type shown in 

 Fig. 24. The process is repeated in succeeding seasons with no 

 essential variation, save that the spermatogenetic wave, as the male 

 becomes older, travels each year over a greater extent of the ante- 

 rior portion of the germ cell cord (represented in black in Fig. 24) 



