124 THE STORY OF LIFE'S MECHANISM. 



the last generation, since the division of the egg 

 in development is like that already described, 

 and always results in producing new cells with 

 the same number of chromosomes as the starting 

 cell. Hence, if the number of chromosomes in 

 the next generation is to be kept equal to that in 

 the last generation, this egg cell must get rid of 

 a part of its chromatin material. This is done 

 by a process shown in Fig. 35. The centrosome 

 divides as in ordinary cell division (Fig. 35), and 

 after rotating on its axis it approaches the surface 



FIG. 36. FIG. 37. 



FIG. 36. The egg centrosomes have changed their position. The 

 male cell with its centrosome remains inactive until the stage 

 represented in Fig. 42. 



FIG.. 37. Beginning of the first division for removing superfluous 

 chromosomes. 



of the egg (Figs. 36 and 37). The egg now 

 divides (Fig. 38), but the division is of a peculiar 

 kind. Although the chromosomes divide equally 

 the egg itself divides into two very unequal parts, 

 one part still appearing as the egg and the other 

 as a minute protuberance called the polar cell (pc' 

 in Fig. 38). The chromosomes do not split as 

 they do in the cell division already described, 



