THE CONTINUITY OF LIFE 



241 



When the chromosomes have assumed definitive form, the pre- 

 liminary events which constitute the prophase of mitosis are 



Fig. 164. — Typical stages of mitosis (somatic) in which the chromosome 

 number is assumed to be eight. A, prophase (start) : chromatin still exhibiting 

 net-like appearance, centrosome divided and surrounded by aster; B, prophase 

 (early): chromosomes visible as long split threads of chromatin, centrosomes 

 moving apart and spindle arising between; C and D, prophases (later): nuclear 

 membrane disappearing, chromosomes shorter and thicker ; E and F, metaphase 

 and anaphase (early): chromosomes arranged in equatorial plate and each 

 separating into two along the longitudinal split; G, anaphase (later): a set of 

 eight chromosomes approaching each aster; H, telophase: gradual loss of 

 visibility of distinct chromosomes, asters and spindle disappearing, division 

 of cytoplasm beginning; I, mitosis completed, two cells. 



brought to a close by the chromosomes being drawn to the center of 

 the spindle. Here they are arranged in a plane at right angles to 

 the long axis of the central spindle, midway between the two cen- 

 trosomes, and form the equatorial plate. 



