SPERMATOGENESIS OF AMERICAN CRAYFISH 



603 



grows to its largest dimensions. For the study of the various 

 states in spermatogenesis, the testicular lobes are in the best 

 conditions of development from the middle of June to the middle 

 of July. During the latter part of July and in August they go 

 to sperm. Testes secured during the latter part of August and 

 in September showed very few of the earlier stages in the sperma- 

 togenesis, nearly all of their tubules were filled with either 

 spermatogonia, spermatids or spermatozoa. In October the 

 tubules are charged with myriads of ripe sperm-atozoa (fig. 78) 

 and the testis has decreased considerably in size. 



Copulation often occurs during the m.onths of September 

 and October and then the sperm of the male is discharged through 

 the vas deferens and stocked in the spermatheca of the female. 

 During the latter part of October, the species goes into hiber- 

 nation and then the testis undergoes little change, remaining 

 practically dormant until the following spring, when favorable 

 weather brings the animals from their burrows. In the early 

 spring another period of copulation may ensue lasting through 

 April and part of May. After this the testis begins rapid growth. 

 The following is a tabulated list of the months of the year and 

 the corresponding condition of the testis during that period. 



TABLE 1 



Copulation 

 occurs 



CONDITION OF TESTIS 



Copulation 

 occurs 



April 

 May 



June 



July 



August 

 September 



October 



November 

 to March 



Testis small and contains germinal epithelial 

 cells, nutritive cells, spermatogonial stages 

 and ripe spermatozoa 



/Testis commences active proliferation and 



\ increases in size 



[Period of greatest activity; all stages in sper- 

 matogenesis are obtainable; testis assumes 

 its maximum size 



/Testis goes to sperm; size remains practically 



\ the same as in July 



/Testis decreases in size and the tubules become 



\ charged with ripe spermatozoa 



/Tubules are almost entirely changed to sper- 



[ matozoa; testis has become very small 



/Hibernation period; no change in testis from 



\ October condition 



JOURNAL OF MORPHOLOGY, VOL. 25, NO. 4 



