SPERMATOGENESIS OF AMERICAN CRAYFISH 625 



9. In the postdiplotene stage a second longitudinal split 

 appears along each arm of the gemini, thus forming four thread- 

 like arms. These now open up, and soon thicken into round 

 chromosomes and form the components of the tetrads. 



10. The nuclear wall breaks through and the tetrads, in the 

 form of dumb-bells, migrate to the equator of the spindle. Each 

 end branch of the dumb-bell consists of two chromosomes parti- 

 ally fused. 



11. The first maturation division is the reduction division. 

 A polar view of the metaphase stage reveals one hundred large 

 chromosomes in Cambarus virilis and one hundred and four in 

 Cambarus immunis. 



12. In Cambarus immunis a clump of eight chromosomes is 

 often seen encircled in a clear vacuole of the cytoplasm, standing 

 apart from the other ninety-six chromosomes. The history 

 of this chromosomal clump could not be traced. 



13. In Cambarus virilis two round, large chromatoid bodies 

 appear in the cytoplasm during the pachytene stage of the 

 growth period. These are enclosed in clear areas of the cytoplasm 

 and are probably formed by a flowing together of the chroma- 

 toid masses found in the cytoplasm during the earlier stages in 

 the spermatogenesis. 



14. During the reduction division, these chromatoid bodies 

 go off, undivided, to one pole of the cell. This is their common 

 mode of behavior. More rarely one goes to one pole, while the 

 other migrates to the opposite pole of the cell. 



15. Three types of secondary spermatocytes are thus produced, 

 type A, containing the two chromatoid bodies, type B, with 

 one chromatoid body, and type C, without any chromatoid 

 bodies. Types A and C are the common ones, whereas type B 

 is comparatively rare. 



16. No distinct rest stage follows between the first and second 

 divisions. The second spermatocyte division is the equational 

 division. A polar view of the metaphase stage of this division 

 shows 100 chromosomes in Cambarus virilis and 104 chromo- 

 somes in Cambarus immunis. The chromosomes are round in 



