42 PHYSICAL EXPRESSION. 



Another important mode of expression in man 

 and animals is that which may be conveniently 

 termed " the coincident development of parts." 

 Observation often shows that two parts of the 

 body usually agree, in having the same proportion 

 of good or ill development. If the one part is well 

 developed, the other part is likewise well developed, 

 and vice versa, although the one pai't is not the origin 

 of the other, or directly connected with its forma- 

 tion. It may probably be shown hereafter that the 

 good or incomplete development of each of the parts 

 thus found to correspond, is the result of some 

 common antecedent or cause, or that both are alike 

 inherited. Thus we see the colour of the hair, and 

 the colour of the iris, often bear a fixed relation to 

 one another ; the height of the body and its proper- 

 ties as indicated by measurement, usually show a 

 marked degree of correspondence in the same race 

 of men, and in animals of the same species if living 

 under similar circumstances. The subject is dwelt 

 upon in the " Origin of Species," p. 115. 



Certain properties of a man or of an animal, are 

 only expressed when external forces demonstrate 

 their existence. The capacity to feel joy is proven 

 by the expression of joy when something happens 

 to the subject producing such emotion. The 

 capacity of colour-sense is demonstrated only by 

 aid of coloured objects. In these cases circum- 

 stances external to the individual help to express 

 the properties in question. 



The property or function heredity is one that must 

 be expressed outside the individual subject. A few 



