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 
ah 
Tiga 
Fic. 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; ¢, 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; 4, cell division completed. (From 
Guyer.) : 
poles of the spindle (Fig. 44, e and f). 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. 
