248 THE HISTORY OF CEEATION. 



those of the left arm. Now, as the special use of the right 

 arm has been adopted and transmitted by inheritance for 

 thousands of years among Europeans, the stronger shape 

 and size of the right arm have already become hereditary. 

 P. Harting, an excellent Dutch naturalist, has shown by 

 measuring and weighing newly-born children, that even in 

 them the right arm is more developed than the left. 



According to the same law of divergent adaptation, both 

 eyes also frequently develop differently. If, for example, a 

 naturalist accustoms himself always to use one eye for the 

 microscope (it is better to use the left), then that eye will 

 acquire a power different from that of the other, and this 

 division of labour is of great advantage. The one eye will 

 become more short-sighted, and better suited for seeing 

 things near at hand ; the other eye becomes, on the contrary, 

 more long-sighted, more acute for looking at an object in the 

 distance. If, on the other hand, the naturalist alternately uses 

 both eyes for the microscope, he will not acquire the short- 

 sightedness of the one eye and the compensatory degree of 

 long-sight in the other, which is attained by a wise distribu- 

 tion of these different functions of sight between the two 

 eyes. Here then again the function, that is the activity, of 

 originally equally-formed organs can become divergent by 

 habit ; the function reacts again upon the form of the organ, 

 and thus we find, after a long duration of such an influence, 

 a change in the more delicate parts and the relative growth 

 of the divergent organs, which in the end becomes apparent 

 even in their coarser outlines. 



Divergent adaptation can very easily be perceived among 

 plants, especially in creepers. Branches of one and the 

 same creeping plant, which originally were formed alike, 



