22 GENETICS 



It was formerly thought by the school of "ovists" 

 that in fertilization the essential process is a stimu- 

 lation of the all important egg by the sperm. The 

 opposing school of "spermists," on the other hand, 

 regarded the egg simply as a nutritive cell the func- 

 tion of which is to harbor the all important sperm. 

 It is now known that both the egg- and the sperm-cell 

 are equally concerned in fertilization, which consists 

 in the union of their respective nuclei within the 

 cytoplasm of the egg. 



7. MATURATION 



Certain preliminary changes of a preparatory 

 nature, termed maturation, regularly precede the 

 union of the nuclei of the two sex-cells in fertiliza- 

 tion. 



These maturing changes result in reducing the 

 outfit of chromosomes in each sex-cell to one half the 

 original number, a process which is necessary in 

 order to maintain the chromosome count which is 

 characteristic for any particular species and which is 

 known to exist unbroken from generation to genera- 

 tion. If there were no such reduction, then the 

 fertilized egg, formed by the union of egg and sperm 

 nuclei, would contain double the characteristic 

 number of chromosomes, and during the formation of 

 a new individual, the number in all the cells arising 

 by mitosis from such a fertilized egg would like- 

 wise be double. When the germ-cells of such indi- 

 viduals unite in fertilization, the original number of 

 chromosomes would be quadrupled, and so on in 



