On the Mechanical Conception of Nature. 663 



As I have already insisted upon above, from 

 the point of view of the conditions of life there is 

 no reason for assuming rapid transformations ; 

 the change of conditions is almost always ex- 

 tremely slow ; and indeed in numerous instances 

 no objective change occurs, but simply a sub- 

 jective one, if we may thus designate those cases 

 in which the alteration in the conditions of life 

 depends upon a change in the animal form which 

 is undergoing transformation, and not in that of 

 the environment. This is the case in the above- 

 mentioned instances of mimicry, where the whole 

 change in the conditions of life arises from one 

 species becoming similar to another. The pro- 

 cess of natural selection has here as long a period 

 of time as it requires to perfect its results. It is 

 quite similar in all cases of special protective 

 adaptations of form and colour. In all these it is 

 always improvement that is concerned, and not the 

 question " to be or not to be " with which we 

 have to deal. 



It is just cases of this last kind, however, 

 which are best fitted for exposing the improba- 

 bility and insufficiency of the assumption of a 

 variational tendency as a distinct directive power. 

 We have only to fix our attention upon some par- 

 ticular case of sympathetic colouring, or, still 

 better, of mimicry. A " tendency to variation " 

 implies that a large number of individuals produce 

 varieties resembling the model to be imitated, and 



