Turning now to our subject proper—namely, playful locomotion or change of place—we find the biological significance of play, the elaboration of certain imperfect instincts, brought out with marked distinctness. The child’s first practice in the direction of future walking is found in the alternative kicking, which is so essential to muscular development.[167] Further progress is marked by raising the body and learning to sit, efforts marking the beginning of the struggle with weights which Souriau regards as the leading stimulus to movement-play. So long as this struggle to retain his equilibrium lasts, the child’s behaviour betrays the direct intention of the play. Preyer says: “In his fourteenth week my sturdy boy easily made his first attempt to sit, having his back well propped. In his twenty-second week the child could raise himself in the effort to reach my face, but not till the thirty-ninth week could he sit alone, and still preferred a back. In his carriage it was necessary for him to hold on even in the fortieth and forty-first weeks. But when for a supreme moment he did manage to sit up unassisted he was evidently delighted, and made the greatest efforts to preserve his equilibrium.”[168] Creeping is an imperfect though genuine sort of locomotion preparatory to walking. “It is a treat,” says Sigismund, “to watch a creeping child. The tiny creature, seated on the floor, longs for something beyond his reach; straining to get it, he loses his balance and falls over. In that position he still stretches his hand out, and notices that he is nearer the object of his desire, and that a few more such forward motions would attain it. Soon he becomes more active, sure, and courageous, and learns to maintain his centre of gravity on three supports while he lifts the fourth member for his next step forward, for at first the child raises but one limb at a time, though he soon learns to use the right hand and left foot together. I have never seen one so use the hand and foot on the same side. Sometimes the child crawls backward like a crab, even when there is nothing before him which he wishes to shun.”[169] Fouquières gives two beautiful ancient representations of creeping children, the first going toward some fruit which lies on a footstool, and the other gazing at a vase on the ground.[170] Children who have a lively desire to roam before they are able to walk invent many expedients which afford them great satisfaction; for example, a little boy, Werner H——, has acquired remarkable skill in getting about by stiffening his arms as he stretches them down at his sides and swinging himself forward as if on crutches, as we sometimes see the unfortunates do who have had both legs amputated.