The error must be guarded against of interpreting in terms of intelligence what is merely the outcome of long-continued structure adaptation. When the limbless lizard called the Slow-worm is suddenly seized by the tail, it escapes by surrendering the appendage, which breaks across a preformed weak plane. But this is a reflex action, not a reflective one. It is comparable to our sudden withdrawal of our finger from a very hot cinder. The Egg-eating African snake Dasypeltis gets the egg of a bird into its gullet unbroken, and cuts the shell against downward-projecting sharp points of the vertebrae. None of the precious contents is lost and the broken "empties" are returned. It is admirable, indeed unsurpassable; but it is not intelligent. Sec. 5 Mind in Birds Sight and hearing are highly developed in birds, and the senses, besides pulling the triggers of inborn efficiencies, supply the raw materials for intelligence. There is some truth, though not the whole truth, in the old philosophical dictum, that there is nothing in the intellect which was not previously in the senses. Many people have admired the certainty and alacrity with which gulls pick up a fragment of biscuit from the white wake of a steamer, and the incident is characteristic. In their power of rapidly altering the focus of the eye, birds are unsurpassed. To the sense of sight in birds, the sense of hearing comes a good second. A twig breaks under our feet, and out sounds the danger-call of the bird we were trying to watch. Many young birds, like partridges, respond when two or three hours old to the anxious warning note of the parents, and squat motionless on the ground, though other sounds, such as the excited clucking of a foster-mother hen, leave them indifferent. They do not know what they are doing when they squat; they are obeying the living hand of the past which is within them. Their behaviour is instinctive. But the present point is the discriminating quality of the sense of hearing; and that is corroborated by the singing of birds. It is emotional art, expressing feelings in the medium of sound. On the part of the females, who are supposed to listen, it betokens a cultivated ear. [Illustration: THE BEAVER The beaver will gnaw through trees a foot in diameter; to save itself more trouble than is necessary, it will stop when it has gnawed the trunk till there is only a narrow core left, having the wit to know that the autumn gales will do the rest.] [Illustration: _Photo: F. R. Hinkins & Son._ THE THRUSH AT ITS ANVIL The song-thrush takes the snail's shell in its bill, and knocks it against a stone until it breaks, making the palatable flesh available. Many broken shells are often found around the anvil.]