ticularly in domesticated animals, because inherent organic conservatism carries into the new state of life habits and instincts useful to the old. The turning round of a dog before it goes to sleep, and what my children call the "kneading-dough" action of a cat when before a warm fire, have been noticed before. But it may be remarked that when a cat takes a piece of meat she invariably gives it a shake—a habit acquired by the wild animal to shake off blood-drops and any adherent grit obtained by the flesh from contact with the ground, but an entirely useless performance in the case of a domestic cat fed on cooked meat in a carpeted room. Ducks which are kept away from a pond will, when it rains, or when they hear the splashing of water, repeatedly raise and lower their heads with a jerking motion—the same action which they use when in the water in order to throw the water over their bodies to wash themselves. Ducks delight in water, and consequently these washing movements are intimately associated with pleasure. Thus they feel pleasure when they are let out after confinement, though they may not be near water; and this pleasure they express by going through the washing movements—in fact, the association is so strong that these movements have become a conventional expression of pleasure of any kind. Young lambs will mount any hillock in a field, because their wild parents were dwellers in mountainous countries. We ourselves, when we wish to express scorn, or contempt, or anger, draw up our lip so as to expose the canine teeth—the weapons with which our monkey ancestors were wont to fight, as has frequently been pointed out. Babies, when they—cry and thus wish to express rage and indignation—draw the mouth into a quadrate shape. This peculiar set of the mouth in a crying infant was noted by Darwin; but the reason for it does not seem to have been grasped. It arises, however, from the fact that crying is associated with anger, that in anger the fighting instinct is dominant, that the fighting instinct leads to a display of weapons on the noli-me-tangere principle, that the weapons of our ancestors were caniniform teeth in the upper and under jaws. It may be observed that the lips of a crying baby's mouth are so disposed as to exactly display the caniniform teeth as much as possible; but here comes the curious part of the whole matter—a young baby shows the quadrate-shaped mouth more remarkably than older children; yet it has no teeth to display, for the teeth are not to be seen in the gums. Here is a habit, acquired for a definite purpose, persisted in afterward when no means are available for fulfilling the purpose, and yet persisted in because of the long association in ancestors of the weapon-display with anger. For a
- Expression of the Emotions, second edition, chapter vi, pp. 155-158.