appear, are diversified, tend to group themselves into a system; at the same time, the animal reacts by more varied movements to external stimulation. But even when the stimulation received is not at once prolonged into movement, it appears merely to await its occasion; and the same impression, which makes the organism aware of changes in the environment, determines it or prepares it to adapt itself to them. No doubt there is in the higher vertebrates a radical distinction between pure automatism, of which the seat is mainly in the spinal cord, and voluntary activity, which requires the intervention of the brain. It might be imagined that the impression received, instead of expanding into more movements, spiritualizes itself into consciousness. But as soon as we compare the structure of the spinal cord with that of the brain, we are bound to infer that there is merely a difference of complication, and not a difference in kind, between the functions of the brain and the reflex activity of the medullary system. For what takes place in reflex action? The centripetal movement communicated by the stimulus is reflected at once, by the intermediary of the nerve centres of the spinal cord, in a centrifugal movement determining a muscular contraction. In what, on the other hand, does the function of the cerebral system consist? The peripheral excitation, instead of proceeding directly to the motor-cells of the spinal cord and impressing on the muscle a necessary contraction, mounts first to the brain,
