2 COLOUR IN NATURE 



exhibit extraordinary constancy. Such markings 

 often tend to reappear in slightly modified forms in 

 a large series of nearly related organisms. Thus 

 Eimer has shown that the markings of the head, 

 often so conspicuous in the domestic cat, tend to recur 

 constantly throughout the whole of the Carnivora, 

 and in a large number of cases may be quite 

 definitely traced. This constancy of colour or 

 marking is not infrequently available for the purpose 

 of classification, or at least of ready identification, 

 and has therefore always attracted much attention. 



But the point of interest about the colours of 

 organisms which has of late had most stress laid 

 upon it is one which, like so many recent develop- 

 ments of biological theory, has grown out of Darwin's 

 work. As is well known, Darwin's statement of the 

 Doctrine of Descent involved a clear formulation of 

 what has become widely known as the Struggle for 

 Existence, but what was in fact the first clear appreci- 

 ation of the intricacy of the relations existing between 

 organisms and their environment, the term including 

 both physical nature and other organisms. Darwin 

 endeavoured to prove that the balance of nature is 

 so finely adjusted that the slightest oscillation of one 

 part may affect parts apparently far removed from 

 it, and that the Struggle for Existence is so keen that 

 all specific characters are, as it were, maintained at 

 the point of the sword. Now we have just seen 

 that the colours and markings have always been 

 recognised as among the most constant of the 

 characteristics of organisms ; if, therefore, all specific 

 characters are preserved by virtue of their usefulness, 

 then surely the colours must be of supreme import- 



