26 THE SCIENTIFIC EVIDENCES OF 



II. 



THE ARGUMENT FROM MORPHOLOGY OR 

 STRUCTURE. 



I NOW pass to another line of argument. The 

 theory of evolution by natural selection sup- 

 poses that hereditary characters admit of being 

 slowly modified wherever their modification will 

 render an organism better suited to a change in 

 its conditions of life. Let us, then, observe the 

 evidence we have of such adaptive modifications 

 of structure, in cases where the need of such 

 modification is apparent. For the sake of clear- 

 ness, I shall begin by again taking the case 

 of the whales and porpoises. The theory of 



