144 Permanence and Evolution. 



less ages its own pet colour and pet arrangement. 

 If these predilections of female birds are to be 

 accounted for by their food, then birds with 

 much blue in their plumage must feed on blue 

 fruits, those with bright yellow on yellow fruits, 

 and how the arrangement of colours is to be 

 accounted for on that principle I cannot guess, 

 nor has Allen given any hint. Even if we find 

 a certain plausibility in Allen's hypothesis, as 

 long as we limit ourselves to divisions of the 

 largest generality, how is it to be applied to 

 closely allied species of the same genus with 

 similar habits ? Allen, for instance, singles out 

 the bullfinch as the most notable of our brighter- 

 coloured finches, and as specially fruit-eating ; 

 but is the bullfinch really brighter than the gold- 

 finch or chaffinch ? Again, why are grass-eating 

 mammalia never green ? According to Allen's 

 theory one would think cattle and sheep ought 

 to be predominantly so. Is it answered that 

 green, through its commonness or any other 



