While the skull-form thus becomes distinctive of brains possessing or lacking certain faculties, it must not be supposed that this relation is an essential one. The brain will perform its work without reference to the shape of the skull. This is proved by the many tribes who have artificially deformed the head in obedience to fashion or superstition. In America it is noteworthy that the crania thus malformed to the utmost degree are precisely those of the nations of the highest civilisation—the Mayas of Central America and the Quechuas of Peru. _The Nervous System._—Professor Haeckel, in his lectures on “anthropogeny,” lays down the maxim, “All soul-functions or psychical activities depend directly on the structure and composition of the nervous system.” This is illustrated by the biological development of the nerves of special sense,—of sight, hearing, taste, and smell. Originally they were all indifferent touch-nerves, and by slow degrees in indefinite time developed their specific reactions. They are yet by no means the same in all persons, as everyone knows. They also differ widely in groups, nations, and races. The study of the “reaction-times” of the principal races has occupied Cattell, Bache, and other psychologists. The sense of taste is notably different. An Eskimo finds pleasure in castor oil and a Kamchatkan in eating rotten fish. The Annamite is almost insensible to pain from wounds, but suffers intensely from moderate cold and is acutely affected by odours. The Fuegian can sleep naked on the snow with comfort, but is easily disturbed by noises. The intellectual differences between both individuals and races arise not so much from relative mental capacity as from varying reaction to mental stimuli. They all have pretty much the same power to pursue knowledge, if they choose to exert it. The difference is one involving the general nerve-tracts. Perception and attention were the forces which in the history of organisms developed all the special senses from nerves of touch; and the growth of the intellect is consequently closely conditioned by the qualities of nerve-sensations. _The Osseous System._—To be asked to define the ethnic life of a group from the bones exhumed in its cemeteries would seem a hopeless task. Yet it is possible, for on the osseous system the whole bodily structure is built up, and the activity of the brain is conditioned. Races differ in their skeletons. That of the African black is heavy, the flat bones thick, the pelvis narrow, and presents many peculiarities which are termed “pithecoid” or ape-like. Contrasting with these are small-boned, delicately formed skeletons of the Indonesians and Japanese, resembling those of the female in other stocks. It would not be difficult to bring the ethnic into relation to these skeletal traits.