Page:Darwinism by Alfred Wallace 1889.djvu/246

 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 markings; and they correspond so exactly in general character with those of the mammalia, already described, that we cannot doubt they serve a similar purpose.

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