CHAPTER VIII.— HEREDITY. 



I. THE QUESTION STATED. 



IT IS the popular belief that characteristics of par- 

 ents are transmitted to their offspring through the 

 medium of the reproductive cells. This opinion is 

 founded on an infinitude of observations easily made 

 on plants, animals, and men, and in fact it is not de- 

 nied as a general statement by anybody. It is a fact 

 of ordinary observation that many and apparently 

 most of the structural characteristics of one generation 

 are inherited by its offspring. Not only is this the 

 case, but the functionings of organs which depend on 

 minute histological peculiarities are inherited. Such 

 are points of mental and muscular idiosyncrasy; of 

 weakness and strength of all or any of the viscera, 

 and consequent tendencies to disease or vigor of spe- 

 cial organs. Darwin has collected in his work on the 

 Descent of Man numerous instances of the inheritance 

 of various tricks of muscular movement of the face, 

 hands, and other parts of the body. But it is a fact 

 of equally ordinary observation that some peculiarities 

 of parents are not, or may not be inherited, and among 

 these may be enumerated mutilations and injuries, as 

 well as characters which are normal. It is then a 

 question of essential importance to ascertain what 



