28 GENETICS 



parently the only portions of these cells that in- 

 variably take part in fertilization. To the new 

 individual developing by mitosis from the fertilized 

 egg into an independent organism, the factors of 

 environment and training referred to in Figure 1 

 are subsequently added. 



When it is remembered that the human egg-cell 

 is only about yi-gth of an inch in diameter, a gigantic 

 size as compared with that of the human sperm-cell, 

 and, furthermore, when one passes in rapid review 

 the marvelous array of characteristics which make 

 up the sum total of what is obviously inherited in 

 man, the wonder grows that so small a bridge can 

 stand such an enormous traffic. A sharp-eyed patrol 

 of this bridge as the strategic focus of heredity is 

 proving to be one of the most effective points of 

 attack in the entire campaign of genetics. 



It is not desirable at this time to discuss possible 

 ways in which the determiners of the heritage, what- 

 ever they may be, are originally packed into the 

 germ-cells, for this question can be more conven- 

 iently considered in a later connection. It is im- 

 portant at present, however, to emphasize the ob- 

 vious conclusion that determiners of heredity must 

 inevitably be present in the germ-cells in order to 

 account for the fact of "organic resemblance based 

 on descent" between parents and their progeny. 



11. THE DETERMINERS OF HEREDITY 



What are the determiners of hereditary qualities ? 

 Do they actually exist in the germ-cells as visible 



