326 THE COLOUES OF ANIMALS 



The supposed causes of colouring suggested by Wallace 

 and Tylor bear no true relation to the effects 



But even greater difficulties are encountered by 

 those who accept Mr. Wallace's and Mr. Tylor 's views 

 ujDon the subject. If colours and patterns were in- 

 variably caused by different kinds of colouring matter 

 or pigment, it might not appear to be very improbable 

 that the kind of pigment, and therefore the kind of 

 colour, might be slightly varied as a result of the 

 causes suggested by these writers : but even then 

 there would not be any foundation for the assumption 

 that the pigments which produce the brightest colours 

 are necessarily more difficult of elaboration than the 

 others, or more likely to be formed by an organism 

 with surplus vitality or upon that portion of the sur- 

 face beneath which the most important functions are 

 performed. A change of chemical composition will 

 nearly always mean the absorption of different rays of 

 light and therefore a different colour ; but the quality 

 of the latter, as measured by our aesthetic sense, will 

 bear no necessary relation to the strain put upon the 

 organism in producing the pigment. 



When, however, we remember that a very large 

 proportion of the colours and patterns distinctive of 

 Bex are only partially dependent upon pigment, the 

 difficulties become insuperable. Let us first consider 

 the case of white, which forms an important part in 



