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This is an address which was delivered at the Leyden Congress of Zoologists on September 19, 1895. The author writes throughout in direct opposition to Weismann. The view, which Weismann maintains, that natural selection is omnipotent, is "a mere exaggeration of Darwinism" and implicitly involves the other view that all existing characters of animals have some utility. Professor Eimer, on the other hand, contends that the law of definitely directed evolution, or orthogenesis, dominates the transformations of the animate world." The variations of living beings follow, in perfect conformity to law, a few definite directions, and do not take place accidentally in the most diverse or in all possible directions. "Natural selection, therefore, cannot play the chief part in the production of forms, for it implies the constant presence of all possible characters. If only a few definite tendencies of evolution predominate, they shape the organic world, and selection has only a subordinate task. The causes of definitely directed evolution are contained in the effects produced by outward circumstances upon the constitution of a given organism. But through the agency of outward influences the constitution must gradually get changed, and thus new directions of development will be produced. The directions of evolution have nothing to do with utility. The facts prove beyond question that numberless characters are produced in living beings which are not useful at all. Professor Eimer defends his view with skill and vigor, and brings forward a large number of facts in support of his contention.

In this volume the literature on the subject is brought together and presented in a popular way. Though the book does not evince any special originality, it is an interesting exposition of the problems connected with the phenomena of sleep. In the first chapter the writer discusses the physical and mental conditions which prevail during sleep, and gives a critical account of the various theories of sleep. The next chapter deals with insomnia, hypnotism, somnambulism, and double personality. The theory is maintained that "the most elaborate and developed states of multiple personality are simply states of total somnambulism." Hypnagogic visions, the elements of the dream consciousness, premonitory dreams, atavistic dreams, etc., are treated in the concluding chapter. The writer believes that "in the psychic life of sleep we are brought into a vaguer and larger world than we are conscious of during waking life, the world of our once-forgotten past, and the world, it may be also, of the forgotten past of the race." A very full bibliography is appended to each chapter.