The play instinct of the child is as old as the race, or older, and is a vitally important factor, not only in physical development, but also in mental development. In its destructive and disorderly activities the child shows the later adult forces in the formative stage. Old instincts and movements that were once self-preservative and of serious meaning to a wild ancestor reappear in the play of children, and, utilized wisely, may under new form become a valuable possession of the adult. There is a great big man, in fact, several possible men, inside every boy. Through his running, jumping, fighting, swimming, through impulse, instincts and emotions he is seeking the man that is in him, and it is by this turbulent and experimental course that he finally comes to the order of maturity. Every boy is a vitally coiled up set of springs pressing to be released. Race-old energies are struggling in him for expression, and play is the normal way to satisfy the great demand. The child may miss some important things and yet get on, but it can not, without severe and lasting harm miss the instinctive activities of play. In play and games the young are re-enacting these old muscular coordinations and developing mind and body on the old foundation. The boy's love of outdoor sports and the adventures of hunting are significant. Those ancestors of ours who hunted and fished and shaped with care their arrow heads were developing a manual skill and thinking power that we inherit. We use our muscles for more varied and possibly more finished purposes, but it is through the patience and practise of their rude lives that we possess the delicate uses of the hands and the finer dexterities of the mind. The boy who goes whistling to the fields, or hunts, or fishes, or swims, is unconsciously reaching out toward later life and is preparing for serious and bigger things. The growing formative period of life is the time for good physical development. Whatever is gained and fixed then is permanent, as it becomes a part of the physiological habits of the individual. The years before twenty decide the future energy stores, and the capacity to endure. Every function enlarged, every gain of power, is additional storage room for energy, to be drawn upon in the coming days of adult stress.