Other even more complicated examples of harmonious adaptation of passively functioning parts are afforded by the markings of animals, such as those of the butterfly's wing. The colours have only a passive rôle, whether they be due to pigments alone, or to structure, or to both combined. When the coloration of a surface undergoes adaptive variation, this cannot be due to any action of the colour, but must depend on adaptation through selection. Yet it is well known that there are many butterfly-wings whose surfaces exhibit different colours and different shades of colour on their different parts, and that in such a way that together they form a picture, that of a leaf, a piece of bark, a stone overgrown with lichen, an eye, and so on. In such a case the individual colour-spots stand in a particular, indirect relation to each other; although they are independent of each other in their variation, they are not indifferent and due to chance, for together they produce a common picture; this is harmonious adaptation of many parts, where the Lamarckian principle is absolutely excluded. It may, perhaps, be objected that this mimetic picture does not arise all at once, but very slowly in the course of long series of generations, and, indeed, of species. This must of course be so; the simple beginnings are complicated and perfected through the course of long ages. This is implied in the principle of selection as we understand it. But does any one suppose that the gigantic antlers of the giant-stag were developed in a few generations? In this case, too, must not numerous races have succeeded each other before the primitive antlers attained this enormous size? If this must be assumed there was abundance of time for the adaptation, through _germinal_ variations, of the secondarily varying parts, the muscles, tendons, nerves, and bones, for all these parts function actively, and can without difficulty meet, in the individual life, the increased claims made upon them by a slight increase in the size of the antlers. For the certain and indubitable consequence of exercise, of increased use, is the strengthening of the functioning parts.