But man spends also on the average at least a third of his whole existence lying in sleep with his head on a pillow of some kind, perhaps the skull of a _Felis Groeneveldtii_ in the case of Pithecanthropus Erectus, and other such better objects, as he made more study of the art of being comfortable. Those who know much of children and sick persons and have watched them in sleep know that the habit of lying on one or other side prevails largely over that of lying on the back. The head being more or less raised by a pillow, the human sleeper, even when lying on his back and more so when lying on his side, is in a potentially and actually sliding position, a fact well known to most persons from their own experience. It is easy to see how such conditions are tending for a third of a man’s whole life to reverse in some degree the direction of his hair and how they act as we saw in the case of the sitting posture. But the very common _lateral_ position in sleep contributes its own peculiar share in pushing the hair towards the spine, ceasing to do so only when the prominent muscular border of the vertebral furrow is reached. I think it will escape no careful observer of these simple facts of man’s resting life, who also notes the remarkable course of the arrows on his back, that the facts and their present explanation fit one another like a Chubb lock and its key. The only alternative suggestion of the facts is that some being with diabolic power has been at work and laying a trap for poor human biologists in the 20th century A.D. In confirmation of this process I would refer to an example which agrees very closely with the above explanation. I knew an invalid suffering from pleurisy and lung-disease who was much confined to bed, spending much of his time propped high up on pillows. He had long dark hair on his back and I was often struck, when examining him, with the remarkable way in which the hairs were dragged upon so that they pointed nearly in a vertical _upward_ direction. Here was a little instance of an undesigned experiment in the dynamics of hair. Hair of the Chest. In the hair-streams on the chest of our chosen three, lemur, ape and man, there are also some remarkable contrasts in the course they take. Fig. 42 shows these in a vivid manner. Precisely as in the case of the hair on the backs of lemurs, apes and man, we find on the chest of those three types a normal direction on the two lower ancestors and an entirely novel arrangement in man; the former, therefore, will need no verbal description.