PHENOMENA OF INHERITANCE 203 



squash bug, are as surely the result of in- 

 herited causes as are the structural differences 

 between those animals. Within the same 

 species different races or lines show character- 

 istic differences in length of life; in the case 

 of man the average length of life is much 

 greater in some families than in others, and 

 life insurance companies take account of this 

 fact. Even within the same organism certain 

 organs or cells are short-lived, whereas others 

 are long-lived; some cells and organs live only 

 through the early embryonic period, while 

 others live as long as the general organism. 



Obesity is another physiological character- 

 istic which may be inherited; the members of 

 certain families grow fat in spite of themselves, 

 while members of other families remain thin 

 however well fed they may be. Here also 

 many factors enter into the result, but it seems 

 probable that the differentiating factor is an 

 hereditary one. Baldness affects the male 

 members of certain families when they have 

 reached a given age, while in others neither 

 care, dissipation nor age can rob a man of his 

 bushy top. Haemophilia, or excessive bleed- 



