To the primitive organic slime, which is the lowest form of life, consciousness can hardly come. The ascidian with its distinct though simple nervous system is a different and much higher being. In its microscopic world some floating particle touches it roughly: the ever-sensitive end of the afferent nerve thrills; the vibrations pass along the nerve-fibres to the central nerve-mass and provoke it into action: forthwith it sends down the efferent nerve a strong impulse which travels out until it reaches a mass of contractile tissue known as a muscle and causes it to shorten. In the ascidian, however, the limits of nerve-life are very narrow--no eye to see, no ear to hear, no separation of one kind of sensation from another, if indeed there be sensation at all, for we do not know whether the ascidian lives like the plant, to itself unknown, or whether it enjoys a twilight of semi-consciousness, feeling dimly its own existence and that of surrounding objects. The movements which it makes do not seem to emanate from consciousness, but always to originate in the contact of some foreign body with the exterior of its organism. The central mass of nervous protoplasm appears never to flash of its own volition nervous energy to the muscle, but only when aroused by an impulse from without. All movements seem to be _reflex_--that is, produced by an impulse passing up from the surface along the afferent nerve to the central mass, and thrown or reflected back, as it were, along the motor nerve to the muscle. Such simple reflex movements occur in all, even the highest, animals as the most primitive expressions of nervous energy. The exigences of lives fuller than that of the ascidian demand, however, other movements, whose complexity is continually increasing as the scale of life is traversed. Keeping pace with this elevation of function is a progressive setting apart of certain parts of the nervous system for certain purposes. In other words, as function or office becomes more complicated and more separate and particular, so also does the anatomy or structure of the nervous system. The whole nerve-life of the ascidian dwells in one cell or central point and a few fibres: that of the man is divided up between some millions of similar cells and fibres, each set aside for the performance of only one act or class of actions. Special powers everywhere require special structure. From the nervous system of the ascidian to that of man is a transition like that from the universal workman of a barbarous society to the complex factory of modern civilization, in which one man does only one little thing, but does this perfectly.