294 



GENERAL BIOLOGY 



of the spindle, as soon as the spindle is fully formed. These 

 are called chromosomes. This completes the first phase 

 (prophase) of division. 



Then the chromosomes that have split lengthwise, each 

 into two equal parts, move apart in halves along the lines of 

 the spindle in two equivalent groups. The centrosome also 

 divides. This is the second phase {metaphase) and climax 

 of cell division. Now there is provided the nuclear material 

 for two daughter cells. 



The two succeeding 

 phases are the reverse 

 of the first two phases. 

 The chromosomes 

 move in the next phase 

 (anaphase) of division 

 to the ends of the 

 spindle, and form two 

 compact groups,which 

 tend to coalesce more 

 or less into a spireme, 

 and a nuclear wall 

 begins to be devel- 

 oped about them and 

 the spindle begins to disappear. Finally, (telophase of 

 division) the chromatin becomes scattered again upon the 

 finer mesh work of the dispersed linin threads, the cell body 

 divides, and the resting stage with which we began, is 

 resumed. The outcome of these processes is that each 

 daughter nucleus receives half of the nuclear material of the 

 mother cell. However, unequally the cell body may be 

 divided, this process guarantees an equitable distribution of 

 the chromosomes in cell descent. 



This is the ordinary indirect process of nuclear division 

 known as mitosis (or karyokinesis) . The figures successively 



Fig. 176. Cell division in growing tissue (sala- 

 mander epidermis). A number of resting 

 nuclei, and three in process of dividing, a, 

 spireme; b, anaphase of division, and c, late 

 anaphase. 



