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 chalcopterus. 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 The 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. 



