268 



HEREDITY AND ENVIRONMENT 



it is not probable that the end has been reached 

 in this regard. We know that cells contain 

 nuclei and chromosomes and chromomeres, 

 centrosomes and plastosomes and microsomes, 

 and we know that some of these parts differ in 

 function as well as in structure. And there is 

 no reason to doubt that if we had sufficiently 

 powerful microscopes we should find still 

 smaller and smaller units until we came at last 

 to molecules and atoms. 



K x h®© 



Fig. 56. Diagram showing union of factors in fertilization 

 and their segregation in the formation of germ cells. With 

 4 pairs of factors (Aa, Bb, Cc, Dd) 16 types of gametes are 

 possible as shown in the two series of small circles at the 

 right. (After Wilson.) 



