Now, consciousness is regarded by an influential school of thinkers as a sort of _deus ex machina_, which, sitting enthroned, and crowned with a capital letter as Will, directs, like a being from another sphere, the doings of the body. It was against the doctrines of this school that Huxley took up arms. They do not concern us here. The will, or volition, as an underlying cause, stands outside the pale of scientific inquiry. It belongs to the wide realm of metaphysics; its plea must be heard in another court. In this part of his contention Huxley was, we believe, unquestionably right from the scientific standpoint. Neither will, nor impulse, nor instinct, nor consciousness itself, should be introduced into any scientific description or explanation of phenomena as a cause of their existence or being, for as such it does not enter into the sequence of events; it is that which metaphysics claims as their _raison d’être_--that which gives them being. Science in this matter should be frankly agnostic--neither affirming nor denying aught. This, of course, is not equivalent to saying that the agnostic position is the true end of human reason. That would only be so on the assumption that the problems of science are the only problems with which that reason can deal. To exclude metaphysics from science is not to exclude it from human thought. As a matter of fact such exclusion is neither possible nor reasonable. But to clearly distinguish the problems of science from those of metaphysics is absolutely necessary, if we are to prevent hopeless confusion of issues. In contending, however, against the introduction of metaphysical doctrines into the region of scientific explanation, Huxley seems to have been carried too far by the force of his own attack. So long as he held to the position that every conscious state has, as its concomitant, a molecular change in the brain, he had all the forces of evolution on his side. But when he said that consciousness is merely the steam-whistle of life’s locomotive, or merely answers to the sound which the animal-bell gives out when it is struck, he takes up another position of far less strategical strength. For whereas the frog from which the physical centres of consciousness have been removed sits crouched and motionless, and “will starve sooner than feed itself, although food put into its mouth is swallowed;” the frog in which conscious situations can take form in unmutilated cerebral hemispheres behaves in a very different manner. It is nothing less than pure assumption to say that the consciousness, which is admitted to be present, has practically no effect whatever upon the behaviour. And we must ask any evolutionist who accepts this conclusion, how he accounts on evolutionary grounds for the existence of a useless adjunct to neural processes.