6 GENETICS 



their method of distribution from one generation to the 

 next. Many questions of the greatest Interest arise con- 

 tinually, the answers to which depend directly on the way 

 this distribution occurs : What difference does it make what 

 kind of parents one has? Can only inferior or mediocre 

 children come from inferior or mediocre parents? Are the 

 children of superior parents certain to be superior? How 

 important a matter is the stock or family from which one 

 is derived? What can we know beforehand about the chil- 

 dren that will be produced by parents of a certain kind? 

 How far can later generations be influenced by selection 

 of the parents in the present generation, and by the way 

 they are mated? What chance is there for the improve- 

 ment of society, of the race, by selective breeding? 



We therefore undertake first a study of these materials 

 and of their distribution from parents of offspring. It will 

 be best to look first at the way in which these materials 

 of heredity were discovered, and at how their method of 

 distribution became known. First a general picture will be 

 presented; later the important matters will be taken up in 

 detail. 



Discovery of the Materials of Heredity. General 

 Sketch of their Method of Action 



Long ago it was discovered, as everyone knows, that 

 a new individual arises, in most organisms, from the union 

 of two small pieces of material that have been called cells, 

 specifically, germ cells. One of these small pieces of ma- 

 terial comes from one parent, one from the other, and the 

 two join to form the beginning of the new individual. The 

 one from the male Is commonly called the sperm cell, while 

 the one from the female is called the ovum, or egg. These 

 two minute germ cells unite, giving what we call the ferti- 



