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THE EVOLUTION THEORY 



When a cell is on the eve of dividing we observe first that the 

 chromatin c-rains, which have till then been scattered throughout the 

 network of the nucleus, approach each other and arrange themselves 



chrsl- 



FiG. 74. Diagram of nuclear division, adapted from E. B. Wilson. A, resting cell 

 with cell-substance (zk), centrosphere (cspk) which contains two centrosomes, nucleolus 

 {kk), and chromosomes (chr), the hist distrilmted in the nuclear reticulum. B, the 

 chromatin united in a coiled thread ; the centrosphere divided into two and giving off 

 rays which unite the halves. C, the nuclear spindle {ks2j) formed, the rays more 

 strongly developed, the nuclear membrane {km) in process of dissolution, the chromatin 

 thread divided into eight similar pieces {chrs), the rays are attaching themselves to the 

 chromosomes. D, perfected nuclear spindle with the two centrospheres at the poles 

 {cspli) and the eight chromosomes (clns) in the equator of the spindle, all now longi- 

 tudinally split. E, daughter-chromosomes diverging from one another, but still 

 united by filaments, the centrosomes [cs) are already doubled for the next division. 

 jP, daughter-chromosomes, quite separated from one another, are already beginning 

 to give off processes ; the cell-substance is beginning to be constricted. G, end of the 

 process of division : two daughter-cells (fe) with similar nuclear reticulum {fk and 

 centrospheres {csph), as in A. 



