THEORY OF EVOLUTION 99 



FIG. 51. The two maturation divisions of the egg. The divi- 

 sions are unequal, so that two small polar bodies are formed 

 one of these subsequently divides. The three polar bodies 

 and the egg are comparable to the four sperms. 



50) come to contain only half the total num- 

 ber of chromosomes. 



When the eggs are fertilized the whole num- 

 ber of chromosomes is restored again. 



THE MECHANISM OF MENDELIAN HEREDITY 



DISCOVERED IN THE BEHAVIOR OF 



THE CHROMOSOMES 



If the factors in heredity are carried in the 

 chromosomes and if the chromosomes are defin- 

 ite structures, we should anticipate that there 

 should be as many groups of characters as 

 there are kinds of chromosomes. In only one 



