268 R. R. HUxMPHREY 



3. The testes of urodeles are more favorable for the determi- 

 nation of interstitial cell correlations. 



a. In the individual lobule the germ cells are all at the same 

 stage of development at any one time, or approximately so. 



b. The caudocephalic movement of a ' spermatogenetic wave' 

 gives a succession of developmental stages in a single testis, each 

 stage localized in a region in which the germ cells are all sim- 

 ilarly developed. 



c. At the close of the cycle the spermatozoa are extruded and 

 only the Sertoli cells remain in the lobule; these soon degenerate. 



d. The lobules are regenerated from residual spermatogonia 

 persisting only in their apices; degenerating and regenerating 

 portions of the lobule are therefore distinct. 



e. Regeneration is so long delayed in some urodeles that it 

 begins only after the degeneration of the emptied lobule has been 

 completely effected ; this results in an even more complete separa- 

 tion of the progressive and regressive phases of spermatogenesis. 



4. The development of the interstitial cells in urodeles is 

 correlated with the regressive phases of the spermatogenetic 

 cycle. 



a. During the initial stages of spermatogenesis only flattened 

 or spindle-shaped cells of the connective-tissue-cell type appear. 



b. These cells may increase in number by mitotic division, 

 this occurring usually before the spermatozoa have completely 

 left the lobule. 



c. Following the extrusion of the spermatozoa, these cells 

 round out, increase greatly in bulk, accumulate lipoids, and 

 become typical interstitial cells. 



d. Such interstitial cells in any urodele have been found to 

 develop chiefly in association with lobules undergoing degenera- 

 tion at the close of the spermatogenetic cycle. 



5. The urodele interstitial cell is but a temporary modifica- 

 tion of a stromal cell. 



a. Interstitial cells developed around an emptied lobule dis- 

 appear when the degeneration of the lobule is effected or soon 

 thereafter. Though many of them degenerate, others clearly 

 revert to the original stromal-cell type. 



