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The author deals in an interesting manner with the importance of certain psychical factors in evolution, most of his examples being taken from bird life. Psychical Selection occurs when certain qualities attributes or tendencies acquire survival value through the impression which they make on others; the impression made on one individual being correlated with the expression of another. 'In psychical selection there is preferential appeal of the best expression; under other forms of natural selection there is differential weeding out, the incidence of which falls initially on the worst individuals, those which are bionomically deficient. Psychical selection works from above downwards; natural elimination works from below upwards. But the net result in either case is the preservation of efficiency'. Psychical Selection is perhaps most clearly manifested in courtship and thus forms an important mechanism in a large proportion of the cases coming under Darwin's Sexual Selection. The greater part of the present paper is concerned with a detailed consideration of the psychology of expression and impression within this field.