We always measure the intelligence of an animal by its power of profiting by experience. Thus, a cat is more intelligent than a rabbit because it can learn more; a dog, for the same reason, is still more intelligent. A purely instinctive animal, one that has no memory, can have no conception of its past, and therefore no idea of its future. It lives wholly in the immediate present; feeling, but not thinking. It acts entirely on inclination, not on reflection. It makes provision for the future, not with any notion of providing, but simply because it has an impulse to a certain course of action, the performance of which gives it pleasure of the kind a child derives from playing or eating, and with the ultimate result of which it is no more consciously concerned than a child. If a caterpillar sheltered in a hole with the idea, founded on past experience, of avoiding danger, his action would be intelligent. If, appealing to a memory in which a great number of complex experiences were stored, he took thought and designed himself a shelter in which provision was made for all sorts of _remembered_ dangers, his action would be rational. But if, making no appeal to the past nor taking thought for the future, he builds only because impelled by an innate impulse, then, no matter how elaborate the edifice he rears, his action is instinctive. Animals low in the scale of life--for example, most insects--appear incapable of learning. But often they are wonderfully equipped by instinct. The details of the behaviour of a small beetle, as quoted from Professor Lloyd Morgan, may not have been quite correctly ascertained, but they are sufficiently accurate for our purpose.