SPERMATOGENESIS OF AMERICAN CRAYFISH 613 



In this species, however, a pecuhar group of eight chromosomes is 

 often seen during the stage. The group stands distinctly apart 

 from the other chromosomes, generally along the periphery 

 of the spindle and seems to be enclosed in a clear vacuole (figs. 

 38, 39, 111 and 112). During the anaphase stage, this group 

 migrates to one pole undivided, and thus, undoubtedly, giving 

 rise to two kinds of secondary spermatocytes, one type contain- 

 ing eight more chromosomes than the other. Even before the 

 anaphase stage, the group of chromosomes may be seen mi- 

 grating to one pole (figs. 37, 113 and 114). In the second sperma- 

 tocyte stage all trace of this chromosomal group is lost. 



Mrazek ('01) has described interesting abnormalities in the 

 testis of Astacus. But in Cambarus immunis the clump of eight 

 chromosomes cannot be regarded as an abnormality, for it is of 

 quite frequent occurrence in the cells. It is also impossible 

 to state whether these chromosomes are accessories, for their 

 behavior could not be traced. 



Interesting abnormal mitotic figures were sometimes seen 

 within the tubules of both species studied. These manifested 

 themselves mainly as tripolar spindles during the first spermatocyte 

 division. Figure 27 shows one of these tripolar divisions in 

 Cambarus virilis when the chromatoid bodies are seen migrating 

 to opposite poles. Mrazek ('01) and Binford ('13) have also 

 observed similar abnormalities in other decapods. 



3. Second spermatocyte stage 



No distinct rest stage follows the first maturation division. 

 The nucleus of the telophase stage of the reduction division is 

 at first crescent-shaped and then it opens up into almost a cir- 

 cular form, but is pale and granular. Very shortly, however, 

 it disintegrates to form the spindle of the second division. No 

 spireme, nor tetrads, nor leptotene rods make their appearance. 

 Prowazek ('02 b) in Astacus fluviatilis and Binford ('13) in 

 Menippe mercenaria also found no distinct rest stage between 

 the primary and secondary spermatocyte divisions. 



The chromosomes line up in the equator of the spindle and 

 appear like dumb-bells (figs. 43, 46, 47, 51, 54). A polar view 



