io6 



THE STORY OF THE LIVING MACHINE. 



egg (Figs. 36 and 37). The egg now divides (Fig. 

 38), but the division is of a peculiar kind. Al- 

 though 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 mi- 

 nute protuberance called the polar cell (pc* in 

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

 do in the cell division already described, but each 

 of these two cells, the egg and the polar body, 

 receives four chromosomes (Fig. 38). The result 

 is that the egg has now the normal number of 

 chromosomes for the ordinary cells of the animal 

 in question. But this is still too many, for the 



FIG. 38. 



FIG. 40. 



FIG. 38. First division complete and first polar cell formed, pc.' 



FIG. 39. Formation of the second polar cell, pc" . 



FIG. 40. Completion of the process of extrusion of the chromatic 

 material \fn shows the two chromosomes retained in the egg 

 forming the female pronucleus. The centrosome has disap- 

 peared. 



egg is soon to unite with the male cell ; and this 

 male cell, as we shall see, is to bring in its own 

 quota of chromosomes. Hence the egg must get 



