We have on another occasion explained that sensations are sense-impressions which have acquired meaning.[18] Rays of light are reflected from an object and fall upon the retina of an eye. Here they produce a disturbance of nervous substance which is transmitted to the brain where it is felt as the image say of a tree. Now the ether-waves are not sight, but a certain form of ether-waves corresponds to a certain form of sight, and the latter comes to stand for the former. The mental picture of a tree becomes a symbol for a special object outside of us and it is projected to the place where experience has taught us to expect that object. In naming objects we repeat the process of expressing by symbols. Sensations are symbols, and names are symbols of symbols. The name and concept tree is not the composite picture of all the trees I have seen, but it is the symbol of this composite picture of sense-impressions. Sensations are like the chords of a piano and the concepts are like the keys. The key is different in kind from the chord which belongs to it. When I touch the key the chord will sound: when I pronounce a name the composite sensation of all its analogous memories will be awakened. * * * * * Can there be any question that difference in kind can originate by degrees? Professor Romanes uses the phrase “different in kind” as synonymous with “different in origin” and therefore declares that human reason and animal intelligence are “different in degree” only. The word “kind,” it is true, is at least as vague as the word species and a naturalist may often be doubtful where to draw the line. Man and monkey are different in kind, and they are also more different in origin than Carl Vogt assumed, for man is not the descendant of any of the monkey families now existent. But this does not disprove that they are of a still remoter common origin or at least that they originated in the same way in some amœboid form as simple life-substance. New formations which originate through combining are as much new creations, i. e. things new in kind, as if they were produced through special-creation acts of God which are said to be creations out of nothing and not mere transformations.