Observation and the testimony of the consciousness seem to attest this dual progress; but they are, according to the parallelist hypothesis, illusions. When I move my arm by a voluntary act, it is not my will, qua act of consciousness, which determines the movement of the arm—for this is a material fact. The movement is produced by the coming into play of groups of muscles. Each muscle, composed of a semi-fluid substance, being excited, contracts in the direction of its greatest length. The excitant of the muscles is also a material fact, a material influx which starts from the motor cells of the encephalon, and of which we know the course down through the pyramidal fascium, the anterior roots of the spinal cord, and the nerves of the periphery to its termination in the motor plates of the muscles. It is this excitement which is the physical, direct, and veritable cause of voluntary movements. And it is the same with all acts and signs, all expressions of our conscious states; the trembling of fear, the redness of anger, the movements of walking, down to the words we utter—all these are physical effects produced by physical processes, which act physically, and of which the mental counterpart has in itself no effective action.
Let it be understood that I am here pointing out one of the forms, and that the most usual, of the parallelist theory. Each author varies it
