22 



HEREDITARY CHARACTERS 



that a new individual is formed by the fusion of two cells, 

 one thrown off from each parent. Now, if each of the 

 gametes which fuse to form the fertilised ovum contained 

 the full number of chromosomes, it is obvious that the 

 number of chromosomes would be doubled every time a 

 new individual was produced. The reducing mode of divi- 



FlG. 14. Diagram showing distribution of chromosomes to daughter cells 

 in the ordinary or somatic form of division. 



sion which has just been described prevents this from 

 happening, and ensures the number of chromosomes re- 

 maining the same in organisms of the same kind from 

 generation to generation. 



But this reduction presents a very considerable difficulty 



FIG. 15. Diagram showing distribution of chromosomes to the daughter cells 

 in the meiotic or reducing form of division. 



with regard to accepting the chromosomes as being the 

 portions of the cell, the individual entities in fact, by which 

 hereditary characters are generally transmitted. To go back 

 to the example of the organism whose cells contain four 

 chromosomes A, B, C, and D. It is quite obvious that when 

 reduction takes place some of the sperms (the sexual cells 



