This conception of the collective nature of the consciousness of complex organisms finds strong support in two classes of facts. First, it finds support in the fact that, if individuals of many of the animal species of an intermediate grade of complexity, such as some of the worms and some of the radiate animals, be cut into two or more parts, each part may continue to live and may become a complete organism by reconstitution of the lost parts. Since, then, we can hardly deny some integrated psychical life to such organisms, some rudimentary consciousness, we seem compelled to believe that this consciousness may be divided into two or more consciousnesses, each of them being associated with the vital activities of one of the parts into which the organism is divided by the knife. Division of the organism into two parts is also the normal mode of reproduction in the animal world. Even the coming into existence of every human being seems to be bound up with the separation of a cell from the parent organism; and his existence as a separate psychical individual seems to result from the same process of physical division. And if one cell, when thus separated from the parent organism, can thus prove its possession of a psychical life by developing into a fully conscious organism, it is difficult to deny that all other cells have also their own psychical lives, even though they may be incapable of making it manifest to us by growing up into complex organisms when separated. The second class of facts that seem to justify this conception of the consciousness of complex organisms are facts which have been studied and discussed widely in recent years under the head of mental dissociation or disintegration of personalities. Such disintegration seems to occur spontaneously as the essential feature of severe hysteria, and to be producible artificially and temporarily in some subjects, when they are thrown into deep hypnosis. In certain of these cases the behaviour of the human being seems to imply that it is the expression of two separate psychical individuals, formed by the splitting of the stream of consciousness and of mental activity of the individual into two streams. The two streams may be of co-ordinate complexity; but more frequently one of them seems to be a mere trickle diverted from the main stream of personal consciousness. Since it is, from the nature of the case, always impossible to obtain any direct and certain proof that any behaviour other than one’s own is the expression of conscious mental processes, it is not possible to prove that such division or disintegration of the personal consciousness actually takes place. But the facts appear to many of the psychologists who have studied them most carefully[20] to demand this interpretation; and this psychical disintegration seems to be accompanied by a functional dissociation of the nervous system into two or more systems each of which functions independently of the