The pleasure accompanying the perception of the ludicrous has been by some attributed to the exercise of certain muscles in the face, and by others to the acquisition of new ideas. But we may safely discard both theories, for the former derives the enjoyment from physical instead of mental sources, and the latter gives us credit for too great a delight in knowledge, even were it thus generally obtained. The enjoyment seems partly to arise from stimulation and activity of mind, excitement being generally agreeable, whereas inaction is monotonous and wearisome. But it seems also partly to be derived from sources which are, or appear to be, collateral. Thus, in the early laughter of pleasure, some solid advantage or gratification, present or future, was always in view, and from men being delighted at their own success, which must often have been obtained at the expense of others, it was an easy transition to rejoice at the failure of rivals. In those primitive times, when people felt themselves insecure, and one tribe was constantly at war with another, there was nothing that gave them so much joy as the misfortunes of their enemies. They exhibited their exultation by indulging in extravagant transports, in shouting, in singing and dancing, and when there appeared some strangeness or peculiarity, something sudden or unaccountable in such disasters, laughter broke forth of that rude and hostile character which we may occasionally still hear among the uneducated classes. It accorded with the age in which it prevailed--a period when men were highly emotional and passionate, while their intellectual powers were feeble and inactive. The two early phases of the ludicrous--those of pleasure and of hostility--containing small complexity, and a large proportion of emotion, are to a certain extent felt by the lower animals. Dr. Darwin has observed an approximation to the laughter of pleasure in monkeys, but he does not connect it with intelligence, and would not, I believe, claim for them any sense of the ludicrous. I have, however, seen a dog, on suddenly meeting a friend, not only wag his tail, but curl up the corners of his lips, and show his teeth, as if delighted and amused. We may also have observed a very roguish expression sometimes in the face of a small dog when he is barking at a large one, just as a cat evidently finds some fun in tormenting and playing with a captured mouse. I have even heard of a monkey who, for his amusement, put a live cat into a pot of boiling water on the fire. These animals are those most nearly allied to man, but the perception of the ludicrous is not strong enough in them to occasion laughter. The opinion of Vives that animals do not laugh because the muscles of their countenances do not allow them, can scarcely be regarded as philosophical. Milton tells us that, "Smiles from reason flow, To brutes denied;"