236 R. R. HUMPHREY 



of spermatogenesis moves toward the cephalic end of the organ, 

 leaving behind it a trail of emptied lobules at the close of the 

 cycle, the development of interstitial cells follows in its wake. 

 It cannot be said that at a certain time of year these cells are 

 in a certain condition; there exists in the testis, from late October 

 to the following spring, a succession of stages in their develop- 

 ment corresponding with the caudocephalic succession in which 

 the lobules were emptied, the youngest stages present being 

 most cephalically located and the oldest caudally, with inter- 

 mediate stages between the two. Hence a study of complete 

 longisections of the testis (rather than of cross-sections through 

 any one region) is necessary if one wishes to determine the extent 

 of development of the interstitial cells at a given time. 



A longisection of the .testis of an animal killed on October 

 30th shows that the anterior portion (about a third) of the organ 

 is still occupied by spermatozoa. This anterior third of the testis 

 is somewhat larger than the caudal portion, which has shrunken 

 to about two-thirds or less of its previous diameter following the 

 emptying of its lobules. Each sperm-filled lobule is distended 

 so as to press upon its neighbors; cross-sections are polygonal in 

 shape. The interstitial nuclei are as previously described for 

 lobules in such a stage; they have become somewhat thickened, 

 but are still disk shaped, with occasional small spherical mito- 

 chondria in their scant cytoplasm. 



The region immediately caudal to this shows the lobules which 

 have been but recently emptied. In these there is evidence of rapid 

 degeneration of the Sertoli cells, which have now completed 

 their period of usefulness. Nuclei pass through the usual degen- 

 eration stages, finally to undergo solution and disappear. Fat 

 demonstrable with osmic acid appears within the lobule. Though 

 it may be present in small droplets in the lobule during the 

 summer, the total quantity appearing then is comparatively 

 small; now, however, the lobule becomes crowded with lipoid 

 droplets of various sizes. 



Around such degenerating lobules the flattened nuclei rapidly 

 round out, their cytoplasm increases in quantity, and cell bound- 

 aries soon become distinguishable. These transformed cells at 



