SPERMATOGENESIS OF AMERICAN CRAYFISH 609 



hence it seems justifiable to conclude that the former represent 

 the latter in number as well as in quality. Recently, Wilson 

 ('12) has strongly upheld this point of view in Oncopeltus and 

 Lygaeus. 



Stage C (figs. 10-11) : Synizesis stage. In this stage the threads 

 drift to one pole of the nucleus and arrange themselves into more 

 or less parallel groups. 



Stage D (fig. 12) : Synapsis stage. The chromosomes have 

 become closely grouped side by side at one pole of the nucleus, 

 while the opposite pole contains a clear open space. 



Stages C and D (figs. 10-12) have been studied in both living 

 and preserved material. In living cells, teased out of the testis 

 and stained by an intravitam stain such as methylin-blue, prac- 

 tically the same figures were seen as those represented in the 

 drawings made from fixed materials. The leptotene threads 

 have all migrated to one pole of the nucleus, leaving in the 

 opposite pole a clear space filled with what appears to be a trans- 

 parent fluid. Figure 11, from a smear preparation, gives a good 

 view of such a cell. Wilson, Morse and others have also studied 

 the contraction phase in living cells of insects and have obtained 

 similat results. Therefore, it is not an artifact due to fixation, 

 but is an actual process occurring in the spermatogenesis. 



During these stages, careful and prolonged study has revealed 

 the paired and parallel arrangement of the leptotene threads in 

 a great number of cases (figs. 10-12). Lerat ('05), has observed 

 a similar arrangement of the leptotene threads in the copepod 

 Cyclops strenuus and the Schreiners, as well as others, have 

 observed it in various other forms. 



Stage E (fig. 13): Pachytene stage. During all the above 

 stages the cell has increased but little in size. Now it begins 

 to grow rapidly and each pair of parallel threads becomes fused 

 into a geminus. The fusion, however, is not complete, for in 

 many of the gemini the longitudinal furrow between the paired 

 leptotene threads may be partially discerned. These gemini 

 soon emerge from the synaptic pole and spread throughout the 

 nucleus. 



