A work of great value to the biologist has been written by one whose work has led him in the widening path of human physiology and its very title is instinct with meaning. The Integrative action of the Nervous System may not aid the systematist or the student of genetics, but for insight into formative powers, where the former can but record facts and find no interpretation, such a work is of supreme importance. When the plant sealed its fate and enclosed itself in a cell-wall and abandoned a life of movement, it was foreordained that its rival would be that cell and its descendants which could adopt a free life, and that the future of the world would lie at the proud foot of that conqueror who could command and mobilize the resources of a nervous system. And, as we know, it has fallen to man to receive the rewards of this promise and potency of a higher life. If one seeks to understand the steps by which man has arrived at his primacy it can only be by the highway of nervous progress, however much the tracing of certain connecting or collateral paths may throw light on contributing causes. So that man’s place in Nature is nearly synonymous with the structural evolution of his brain, as Huxley has shown in his clear and simple manner. Even if man is to remain still an animal Melchisedec for generations to come, or to put it lower, a foundling, no future discoveries that can be imagined will disprove Huxley’s declaration, “Evolution is no longer an hypothesis, but an historical fact.” And yet if man has become adapted to his world, and, in it, crowned with glory and honour by the unfolding of some original complexity, or as the result of some fortunate mutations in the distant past, the human brain, with its cranial capacity of nearly three times the number of cubic centimetres to that of the gorilla, has been making false claims to a paramountcy over all factors in the wonderful initiative of fresh capacities and their mobilisation for conquest. Nothing less than such a “claim” was understood by the ancients, and, though metaphysics had to supply the lack of anatomy and physiology, it has always been held that mind was lord of matter, and now scientific research has told us why. But no one, even the most hard-shelled scholastic, can refuse to the brain organ its predominant share in the making of man. This is seen even in the frigid sphere of science by the difference of interest there is shown between any great discovery bearing on the evolution of man, or on some new lower animal form. When Sir. H. H. Johnston astonished zoologists in 1901 by his discovery and proof of the existence of an archaic large mammal which had been interned for an incalculable time in the Semliki Forest, the thrill felt at that historic meeting passed off very soon when the leading British biologist had monographed the Okapi, settled its name and surname and introduced it into text-books. This is never the fate of such