130 THE STORY OF LIFE'S MECHANISM. 



there appear to be, in the future history of this 

 egg, any actual fusion of the chromatic material, 

 the male and female chromosomes perhaps always 

 remaining distinct. 



While this mixture of chromosomes has been 

 taking place the centrosome has divided into two 

 parts, each of which becomes surrounded by an 

 aster and travels to opposite ends of the nucleus 

 (Fig. 42). There now follows a division of the 

 nucleus exactly similar to that which occurs in 



FIG. 43. 



FIG. 44. 



FIG. 43. An equatorial plate is formed and each chromosome has 



split into two halves by longitudinal division. 

 FIG. 44. The halves of the chromosomes have separated to form two 



nucleii, each with male and female chromosomes. The egg has 



divided into two cells. 



the normal cell division already described in 

 Figs. 28-34. Each of the chromosomes splits 

 lengthwise (Fig. 43), and one half of each then 

 travels toward each centrosome to form a new 

 nucleus (Fig. 44). Since each of the four chromo- 

 somes thus splits, it follows that each of the two 

 daughter nucleii will, of course, contain four 

 chromosomes ; two of which have been derived 

 from the male and two from the female parent. 



