THE TREATMENT HISTORICAL 93 



been superfluous to explain these on the present 

 occasion ; for a far more detailed account than 

 could have been attempted in these pages has 

 recently appeared. 1 Among the older records 

 I have made a point of bringing together the 

 principal observations scattered through the note- 

 books and collections of W. J. Burchell. These 

 have never hitherto found a place in any memoir 

 dealing with the significance of the colours of 

 animals. A few new observations which seemed to 

 be of special interest have been included, together 

 with some fresh considerations deserving of atten- 

 tion in the study of Mimicry in relation to sex. 



INCIDENTAL COLOURS 



Darwin fully recognized that the colours of 

 living beings are not necessarily of value as 

 colours, but that they may be an incidental result 

 of chemical or physical structure. Thus he wrote 

 to T. Meehan, Oct. 9, 1874:- 



' I am glad that you are attending to the colours of di- 

 oecious flowers ; but it is well to remember that their 

 colours may be as unimportant to them as those of a gall, 

 or, indeed, as the colour of an amethyst or ruby is to these 

 gems.' 2 



Incidental colours remain as available assets of 

 the organism ready to be turned to account by 

 Natural Selection. It is a probable speculation 



1 Poulton, Essays on Evolution, Oxford, 1908, 293-382. 



* More Letters, i. 354, 355. See also the admirable account 

 of incidental colours in Descent of Man (2nd edit., 1874), 261, 

 262. 



