CHROMOSOME COMPLEX OF SPERMATOCYTES. 



317 



it was united and has divided longitudinally as usual. But be- 

 sides the accessory and the ordinary dyads of the second sper- 

 matocyte, there is present in each cell a tetrad which was a part of 

 the multiple chromosome and which did not undergo division in 

 the first spermatocyte. This may be found occupying on the 

 second spermatocyte spindle such a position as tetrads usually 

 occupy in the first spermatocyte, and under these circumstances 

 it divides in the customary longitudinal manner. Here again 

 there is a heterotypical mitosis along with the ordinary type, a 

 condition which was also present in the spermatogonia. In both 

 cases there is indisputable evidence that the plane of separation 

 is along the original longitudinal split of the chromatin thread. 



a 



FIG. 13. Early anaphase of first spermatocyte in Mermiria. Only one pole 

 of the spindle in the section and a few of the chromosomes. The method of the 

 dyad separation shown in the tetrads. At the right of the spindle is represented a 

 tetrad derived from the decad. Similar elements are shown in "a" and "/>." At 

 " f" is drawn the same structure in the telophase, where the homogeneous character 

 of the accessory chromosome is in evidence. 



A careful enough study of these cells has not yet been made 

 to determine whether the pair of chromosomes in the second 

 spermatocyte that remain united is the one which reappears in 

 the spermatogonia of the next generation or not. It may not be 



