CHAPTER III. INTRODUCTORY SKETCH. Natural science has shown us how the existing colouration of an animal or plant can be laid hold of and modified in almost infinite ways under the influence of natural or artificial evolution. It shows us, for example, how the early pink leaf-buds have been modified into attractive flowers to ensure fertilisation; and it has tracked this action through many of its details. It has explained the rich hue of the bracts of _Bougainvillea_, in which the flowers themselves are inconspicuous, and the coloured flower-stems in other plants, as efforts to attract notice of the flower-frequenting insects. It has explained how a blaze of colour is attained in some plants, as in roses and lilies by large single flowers; how the same effect is produced by a number of small flowers brought to the same plane by gradually increasing flower-stalks, as in the elderberry, or by still smaller flowers clustered into a head, as in daisies and sunflowers. It teaches us again how fruits have become highly coloured to lure fruit-eating birds and mammals, and how many flowers are striped as guides to the honey-bearing nectary. Entering more into detail, we are enabled to see how the weird walking-stick and leaf-insects have attained their remarkable protective resemblances, and how the East Indian leaf-butterflies are enabled to deceive alike the birds that would fain devour them, and the naturalist who would study them. Even the still more remarkable cases of protective mimicry, in which one animal so closely mimics another as to derive all the benefits that accrue to its protector, are made clear. All these and many other points have been deeply investigated, and are now the common property of naturalists. But up to the present no one has attempted systematically to find out the principles or laws which govern the distribution of colouration; laws which underlie natural selection, and by which alone it can work. Natural selection can show, for instance, how the lion has become almost uniform in colour, while the leopard is spotted, and the tiger striped. The lion living on the plains in open country is thus rendered less conspicuous to his prey, the leopard delighting in forest glades is hardly distinguishable among the changing lights and shadows that flicker through the leaves, and the tiger lurking amid the jungle simulates the banded shades of the cane-brake in his striped mantle. Beyond this, science has not yet gone; and it is our object to carry the study of natural colouration still further: to show that the lion's simple coat, the leopard's spots, and the tiger's stripes, are but modifications of a deeper principle.