CELLS IN DIVISION 



centre is closely followed by a group of chromosomes on the inner side 

 of the nuclear membrane (Figure 41). 



These examples, among others, clearly show that the effects of the 

 achromatic figure on the chromosomes may be seen before metaphase 

 is reached. Nor does the congression of the chromosomes to the meta- 

 phase plate always follow a simple course; a remarkable instance of 



\ 



Figure 41 Spermatocytes of Anisolabis maritima, showing movement of 

 centrioles and chromosomes during diakinesis. a Early stage. Double 

 centriole in cytoplasm. Autosomes at the periphery, b-d They follow the 

 movement of the centrioles. The sex chromosomes on left in c and d are 

 not affected. From Schrader^^' {By courtesy, J. Morph.). 



an apparently premature movement of the chromosomes on the spindle 

 has been described by Hughes-Schrader,^^^ again in the spermatocytes 

 of Mantids, and also in the related Phasmids (the stick insects^^"). The 

 second bouquet polarization comes to an end when the nuclear mem- 

 brane disappears; the spindle is then very rapidly formed, and the 

 orientation of the ends of the chromosomes is exchanged for one in 

 which the centromeres of each bivalent separate, each towards one 

 pole of the spindle, just as in anaphase (Figure 42). The ends of the 



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