SPERMATOGENESIS OF THE RABBIT. 2QQ 



chromosomes of the spermatogonial division. At times they 

 may be traced because of a slightly more rounded form than the 

 other chromosomes. The chromosomes in general are elongated 

 in shape although the tendency is towards a spherical form. 



During the anaphase (Fig. n), the divided chromosomes move 

 toward opposite poles. As soon as the chromosomes reach the 

 pole, they go into a resting stage, the new nuclear wall appearing 

 immediately. The new cell walls may not appear until late in 

 synezesis. The outlines of the new nuclei are first somewhat 

 elongated, conforming to the rough outline of the massed chromo- 

 somes. Gradually these assume a more spherical shape, the 

 spindle-fibers disappear, and the primary spermatocytes are 

 ready for the growth period. 



3. EARLY MATURATION STAGES. 



While the number of chromosomes is not large in the rabbit, 

 the difficulties encountered in counting chromosomes were great 

 indeed. In all of the material, the tendency of the chromosomes 

 to mass was, as already mentioned, very much in evidence, and 

 the most careful tecnhique in fixing and staining did little to make 

 the results more satisfactory. There were enough cells in which 

 chromosome counts were possible to place the probable number 

 as twenty-two in the spermatogonia and twelve in the primary 

 spermatocyte. 



It was found that twenty-two chromosomes went to each 

 pole in the spermatogonial division. After synapsis has taken 

 place, the number is twelve, showing that two of the elements 

 remain single. These two elements are the accessory chromo- 

 somes. Thus the twenty ordinary chromosomes of the spermato- 

 gonia reduce to ten bivalents in the primary spermatocytes, 

 w r hile the two accessories do not undergo synapsis. As will be 

 seen, the later behavior of these univalent chromosomes is 

 entirely distinct from that of the others. 



The early prophases of the primary spermatocytes show all 

 but two of the chromosomes which passed to the poles in the 

 spermatogonial division to grow irregular in shape, and finally 

 weave out into fine strands which immediately spread throughout 

 the nucleus (Fig. 12). All of the irregular masses spin out into 



