SPERMATOGENESIS OF AMERICAN CRAYFISH 611 



growth period and the cell is now ready to undergo mitosis and 

 reduction. 



Stages E to H (figs. 13-23) follow each other in regular succession 

 and the cells have increased a good deal in size. These stages 

 may therefore be regarded as the actual period of growth, while 

 stages A to D (figs. 8-12) are the preparatory steps, preparing 

 the cells for growth. 



b. The cliromatoid bodies. In Cambarus virilis two chromatoid 

 bodies (figs. 13-16, 18, K, and figs. 82-84) make their appearance 

 in the cytoplasm during the pachytene stage (fig. 13, K). Be- 

 fore this, the cytoplasm of the cells contain a distinct idiozome 

 (/), with its centrosome (C), and larger granular masses of 

 mitrochondria {M), which stain like chromatin, but somewhat 

 lighter. Traces of chromatoid masses can also be seen (figs. 

 1-2, 8, k). These chromatoid masses and the mitochondrial 

 granules, however, decrease in size and disappear during the 

 early growth period. In the pachytene stage they have almost 

 completely disappeared. At the same time, two circular bodies, 

 surrounded by more or less clear areas, make their appearance 

 in the cytoplasm; these stain deeply, like the chromatin of the 

 nucleus, and are the chromatoid bodies (fig. 13, K), and it seems 

 as if they were formed by a flowing together of the above men- 

 tioned chromatoid masses (figs. 1-2, 8, k). Wilson ('13), has 

 found a similar body in Pentatoma and believes it to originate 

 in the same fashion. 



c. Reduction division. After the formation of the tetrads the 

 centrosomes are observed to migrate to opposite poles and the 

 nuclear wall breaks down (figs. 22-23). In figure 23 only one 

 of the chromatoid bodies is seen. Next, the tetrads are drawn 

 into the equator of the cell and there arrange themselves for 

 division. During the growth period numerous karyosomes 

 were found in the nucleus, but now these have all disappeared 

 from view.' 



In the metaphase condition the tetrads appear as two large 

 bivalents connected in the form of dumb-bells (figs. 24 and 26). 

 No split can be noticed in either of the bivalents, where the 

 equational division of the second matm^ation stage will occur. 



