292 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



and the spindle-fibers ultimately come to lie at the equator of the 

 spindle as shown in Fig. 44, d. Each chromosome splits lengthwise 

 to form two daughter chromosomes which then diverge to pass to the 



41 



&, 4 



FIG. 44. Diagram showing representative stages in mitotic or indirect cell- 

 division, a, resting cell with reticular nucleus and single centrosome; b, the 

 two new centrosomes formed by division of the old one are separating and the 

 nucleus is in the spireme stage; c, the nuclear wall has disappeared, the spireme 

 has broken up into six separate chromosomes, and the spindle is forming between 

 the two centrosomes; d, equatorial plate stage in which the chromosomes occupy 

 the equator of the spindle ; e, f, each chromosome splits lengthwise and the daughter 

 chromosomes thus formed approach their respective poles; g, reconstruction of 

 the new nuclei and division of the cell body; h, cell division completed. (From 

 Guycr.} 



poles of the spindle (Fig. 44, e and/). Thus each end of the spindle 

 comes ultimately to be occupied by a set of chromosomes. Moreover, 

 each set is a duplicate of the other, because the substance of any 

 individual chromosome in one group has its counterpart in the other. 



