INTRODUCTION S 



colour have some connection with physiology, or 

 are at least not wholly accounted for when their 

 usefulness is proved (see Mr. Beddard's Animal 

 Coloration, and, for the general question, Mr. Bate- 

 son's great work on Variation). 



Having now justified the intrusion of the bio- 

 logist into what appears to be the domain of the 

 physicist, we are at liberty to face the phenomena 

 of colour as they appear in organisms. As, however, 

 the relation of colour phenomena to the theory of 

 Natural Selection has had so much attention bestowed 

 upon it, we do not propose, at least in the first place, 

 to consider it here, but rather to direct attention to 

 the chemical, and^ where possible, to the physio- 

 logical aspects of the colours and pigments of 

 organisms. In a final summary it will be necessary 

 to consider the bearing of the facts upon theories. 



