604 NATHAN FASTEN 



3. Zones of proliferation in the testis 



An examination of the testis during the period of most active 

 proUferation (July), reveals every stage in the spermatogenesis 

 in each of the three lobes comprising the testis. Proliferation 

 always begins along the blind end of each of the lobes, and from 

 this zone the various stages in the spermatogenesis follow each 

 other in more or less regular succession. First <;ome the sperma- 

 togonial stages, then the growth periods, next the maturation 

 divisions and finally the ripening of the spermatozoa. The 

 cells of each tubule are generally in the same stages of develop- 

 ment. Figure 79 shows a cross-section through many of the 

 tubules. 



SPERMATOGENESIS 



The following description is devoted mainly to the sperma- 

 togenesis of Cambarus virilis. The speniiatogenesis of another 

 species of Cambarus was also studied and the main stages were 

 found to be similar to those in Cambarus virilis. This second 

 species could not be determined with accuracy, for only pre- 

 pared slides, obtained from Mr. Powers of Lincoln, Nebraska, 

 were available for study. On corresponding with Mr. Powers 

 it was ascertained that the species had not been identified by 

 him at the time the slides were prepared. He supplied me, 

 however, with a few young crayfish taken from the same stream 

 as those from which the slides were made and these were identi- 

 fied as Cambarus immunis. Therefore it is highly probable 

 that the sections in question were from that species. 



1. Spermatogonial stages 



During the period of active proliferation the tubules in the 

 blind ends of the testicular lobes are filled with spermatogonial 

 cells in all stages of development. Many nutritive cells are 

 also found imbedded in a mass of protoplasm representing 

 a syncitium. These last cells (nutritive cells), appear oval, 

 irregular or circular in shape and contain masses of chromatin 



