Sensations are, then, by no means such original and simple elements of mind as often conceived; but they are developed forms of some general undifferentiated cognitive state, sensation as bare apprehension of bodily disturbance, and this itself cannot be accounted absolutely original. The evolution into particular modes of sensation, as sense of heat, hunger, light, pressure, etc., is in the struggle for existence gradually achieved, and also therewith the evolution of special sense-organs. And we must always bear in mind that it is not the sense-organ that develops the sensation, but on the contrary the effort at sensing that produces, maintains, and improves the sense-organ. The eagle’s eye has been developed by unceasing straining as incited by the necessities of existence felt in pain and pleasure. It is natural for us at our stage of development to suppose that the organs of sense _give_ sensations and to explain the sensation by the physiological organ; but when we reflect that sensations _come_ to us from the organ only up to the measure of the momentum from heredity, we see the insufficiency of purely physiological interpretation. Evolution to-day is on the same basis as evolution at any period, and as it always has been, it always will be, dependent upon a ceaseless _nisus_. It is only by painstaking effort—labour—that man progresses in sensibility, and this effort has always an incentive in some form of interest that is pleasure-pain basis. Thus it is that the astronomer’s eye, the microscopist’s eye, the artist’s eye, is formed. The multiform sensibility of the tea-taster is attained by assiduous tasting, and the development in organ only follows _pari passu_. What is seemingly simple and original in sensation for us was, no doubt, like the very special forms of sensibility acquired by our specialist, achieved by the lower forms painfully and toilfully, and passed on to us. Our highest feats of sensation and insight may likewise for our remote descendants be intuitions, whose apparently simple nature may be asserted as the basis of philosophic systems. A genius is one who antedates the general stage of progress of his period by having as intuitions, as seemingly direct and simple knowledges and sensations, what is beyond or barely within the intensest effort of his contemporaries, though it may become common and easy for all men of later ages.