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- 
