A Theory of Development and Heredity. By Henry B. Orr,
Ph.D. (Macmillan and Co.)—The author thinks that recent authors have attributed too much influence to natural and sexual selection in the gradual evolution of species, and argues that the constant action of surrounding forces upon the organism has been under- rated. The organism would respond more easily to impressions from without the oftener they were repeated ; and by inherited force of habit and association, the earlier phases of development thus induced would take place further and further back, thus enabling fresh influences to act upon the organism, to produce fresh results. This view the author thinks of general application to all daises of phenomena, and likewise thinks that constant stimuli are necessary to insure development. The degraded forms which parasites sometimes assume, and the rudimentary eyes of cave-animals, he likewise regards as due, not so much to disuse, or to the economising of vital forces, as to the absence of the stimuli necessary to produce or to maintain proper development.
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