224 
DARWINISM 
CHAP. 
will serve to illustrate this difference ; which is frequently much 
greater and modified in an endless variety of ways (Fig. 22). 
Numbers of species of pigeons, hawks, finches, warblers, 
ducks, and innumerable other birds possess this class of mark¬ 
ings ; and they correspond so exactly in general character with 
Cursorius clialcopterus. C. gallicus. 
Fig. 21.—Secondary quills. 
those of the mammalia, already described, that we cannot 
doubt they serve a similar purpose. 1 
Those birds which are inhabitants of tropical forests, and 
which need recognition marks that shall be at all times 
visible among the dense foliage, and not solely or chiefly 
during flight, have usually small but brilliant patches of colour 
1 Tlie principle of colouring for recognition was; I believe, first stated in 
my article on “ The Colours of Animals and Plants ” in Macmillan’s Magazine, 
and more fully in my volume on Tropical Nature. Subsequently Mrs. Barber 
gave a few examples under the head of “ Indicative or Banner Colours,” but 
•she applied it to the distinctive colours of the males of birds, which I explain 
on another principle, though this may assist. 
