176 SOME RECENT DEVELOPMENTS 



cell protoplasm alone. The chromatin loops now 

 begin to move from the equator along the threads 

 of the spindle, towards its poles. This takes place 

 in a perfectly regular manner, the sister-threads of 

 each pair moving towards opposite poles. As the 

 two sister-threads of each pair are precisely equal, 

 the two groups of threads around the two poles of 

 the spindle will contain precisely equal quantities of 

 chromatin. The two groups separate completely 

 from each other, and each group becomes arranged 

 in a manner corresponding to that of the primary 

 threads in the original nucleus. In this way two 

 daughter-nuclei are formed by division of the 

 mother-nucleus : each daughter-nucleus containing 

 half the chromatin of the mother-nucleus. After 

 completion of the daughter-nuclei, the protoplasm 

 of the cell-body divides, precisely as in the process 

 of direct division, and the division of the mother- 

 cell into two daughter-cells is complete. 



The above description of the phenomena of 

 mitosis or indirect nuclear division, represents the 

 generally accepted view as to the sequence of 

 events, but several points in it are still very 

 imperfectly understood. One of the most important 

 of these is the origin of the nuclear spindle and 

 its pole-bodies. Van Beneden, whose long- 

 continued and extraordinarily careful observations 

 entitle him to speak with great authority, maintains 

 that the pole-bodies are of primary importance. 

 He says that the pole-bodies appear before the 

 spindle ; that they arise distinctly in the cell 

 protoplasm, quite independently of the nucleus ; 



