4 COLOUR IN NATURE 



an organism is not an isolated characteristic forced 

 upon it, as it were, from without, but may be merely 

 the outward expression of its constitution, we may 

 surely hope not only to be delivered from many 

 laborious hypotheses as to the use of colour in 

 particular cases, but also may perhaps learn some- 

 thing of the physiology of colour. The subject is 

 at least now sufficiently important to merit con- 

 sideration from a purely physiological standpoint. 



We thus see that there are three reasons why it 

 is desirable that the Biologist should concern himself 

 with Colour in organisms. The first is the con- 

 spicuousness of colour phenomena in a merely 

 objective survey of animals and plants ; the second 

 is the relation of these colours to current theories 

 of evolution ; and the third is their importance in 

 comparative physiology. 



The order of arrangement of these three is not 

 purely formal, but to some extent corresponds to 

 the historical order in which the subject has been 

 studied. Before Darwin, the colours of organisms 

 were chiefly studied as convenient marks by means 

 of which the organisms could be recognised.. When 

 Darwin put forward his theory, which is based on 

 the supposition that all specific characters are of 

 supreme importance, it was a natural deduction 

 from the constancy of many colours that these must 

 be of great importance, and so we have all the 

 modern theories of colour (see Mr. Poulton's Colours 

 of Animals). Again, now that the theory of Natural 

 Selection is no longer the centre of men's thoughts, 

 and search is being made for a deeper analysis, it is 

 recognised that it is probable that the phenomena of 



