292 G. J. BOMANES'S MENTAL EVOLUTION IN ANIMALS. This is now explained to mean that, while " a stimulus which evokes a reflex action is at most a sensation," on the other hand " a stimulus which evokes an instinctive action is a perception ". It might be expected from this that Dr. Eomanes would agree with Lewes in speaking of unconscious sensations. But he refers to Lewes's definition of a sensation, as simply the reaction of a sense-organ, only to reject it, and goes on to say that " the diffi- culty of determining whether or not this or that particular low form of life has the beginnings of Sensation is one and the same as the question whether it has the beginnings of Consciousness " . (p. 79). According to this statement, wherever there is sen- sation there is consciousness ; and from this it seems to follow that some reflex actions that is to say, those which are excited by sensations are accompanied by consciousness. But, according to the definition, these are instincts. Instinct, therefore, by the definition (as it is now interpreted), seems indistinguishable from reflex action. The constructive and psychological part of the present volume is less successful than the part that serves as a supplement to Animal Intelligence. Apart from all differences of opinion on purely philosophical questions, which the author desires to avoid, the treatment of the fundamental question of the relation of Mind and Body can hardly be described as satisfactory. It is quite possible, without implying any metaphysical doctrine, to regard mental and physical changes always as concomitants, never as causes and effects of one another. In some places Dr. Eomanes seems to be unwilling to take up this position for fear of com- mitting himself to some definite system of metaphysics. In the following passage his words imply that its evidence is that of a directly observed fact. " We know by immediate or subjective analysis that consciousness only occurs when a nerve-centre is engaged in such a focussing of vivid or com- paratively unusual stimuli as have been described, and when as a prelimi- nary to this focussing or act of discriminative adjustment there arises in the nerve-centre a comparative turmoil of stimuli coursing in more or less unaccustomed directions, and therefore giving rise to a comparative delay in the occurrence of the eventual response. But we are totally in the dark as to the causal connexion, if any, between such a state of turmoil in the ganglion arid the occurrence of consciousness " (p. 75). Notwithstanding the statement in the last sentence, Dr. Eomanes sometimes appears to think that the occurrence of con- sciousness is somehow explained if it can be shown to arise when there is an increase in the time taken up by the transmission of a stimulus. " Consciousness," he says, " is but an adjunct which arises when the physical processes owing to infrequency of repe- tition, complexity of operation, or other causes involve what I have before called ganglionic friction" (p. 113). When the nerve-centre has become "a seat of comparative turmoil among molecular forces " it " begins to become conscious of its own work-
