SPERMATOGENESIS OF AMERICAN CRAYFISH 607 



observed the same things to occur in the spermatogenesis of 

 Menippe mercenaria. 



The nuclear wall soon breaks down and the chromatin masses 

 arrange themselves at the equator of the spindle (fig. 3). Dur- 

 ing the metaphase and anaphase, the centrosomes at either pole 

 are often found to be double and the mitochondrial granules are 

 distributed around the very delicate and slender spindle fibers 

 (figs. 3 and 5). This is similar to what Prowazek ('02 b) found 

 in Astacus. 



A polar view of the metaphase stage is shown in figure 4. 

 The chromosomes are. distributed throughout the whole plane 

 of the equator and are so numerous that ordinarily they cannot 

 be counted. But on the customary inference that there are al- 

 ways twice the number of chromosomes in the spermatogonial 

 stage that can be found at the reduction period, there must be 

 two hundred chromosomes in Cambarus virilis and two hundred 

 and eight in Cambarus immunis. The chromosomes are spher- 

 ical in shape and situated close to one another. In only one case 

 in Cambarus virilis was a good count obtained (fig. 4), showing 

 two hundred chromosomes. 



During the anaphase stage (fig. 5) the chromosomes move to 

 opposite poles. The mitochondrial granules and the double 

 nature of the centrosome can still be discerned. 



In the early telophase stage the chromosomes are at opposite 

 poles and a constriction in the central portion of the cytoplasm 

 makes its appearance. This grows inward and as it does so it 

 constricts the spindle fibers (fig. 6) towards the center, where a 

 thickened heavily staining zwischenkorper (fig. 7, Zw) is formed. 

 A nuclear wall now makes its appearance around the chromosomes 

 at either pole (figs. 6-7) and the division of the spermatogonial 

 cell is almost completed. At first the nucleus is crescent-shaped 

 (figs. 6-7), but as the constriction between the mitotic cells 

 becomes more apparent and the spindle fibers disappear, it 

 gradually assumes its normal round appearance and the chromo- 

 somes distribute themselves throughout the nuclear territory 

 (fig. 8), in order to begin their growth period. These cells 

 represent primary spermatocytes in their earhest stages. 



