THE LIVING ORGANISM 223 



other from a female parent. If the fusion of the 

 two nuclei took place, there would obviously be 

 at each generation a doubling of the amount 

 of nuclear matter and twice the normal number 

 of chromosomes. Nature arranges against 

 this by a remarkable preparation of each 

 parental nucleus. In each first division which 

 occurs in each parental cell before the male 

 and female elements come in contact, only 

 half the usual number of chromosomes is 

 formed, then for some unknown reason, a 

 re-arranging division occurs with the usual 

 number of chromosomes, but half the amount 

 of material in each one. At each of these 

 preparatory divisions in the female cell, one 

 of the two nuclei formed is extruded from the 

 cell and atrophies. The female cell does 

 not divide as a whole in these two divisions : 

 only its nucleus divides. After the completion 

 of this curious process, which is known as 

 maturation, a reduced male nucleus and the 

 reduced female nucleus unite to form a 

 first mixed nucleus to the fertilized ovum, 

 in which the two sexes obviously share 

 equally. The purpose of the rejection of a 

 part of each nucleus has caused much dis- 

 cussion, and is not yet at all clear, but it is 

 probably closely concerned with heredity 

 and species preservation. 



