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THE POPULAR SCIENCE MONTHLY.

specialization determined by the manner of the distribution of strains as is so often found among the lower groups, such as the horses, sloths, jumping-mice, and even-toed ungulates."

In another memoir[1] Dr. Ryder considers the mechanical motion in forming and modifying teeth. Considering first the simplest form of movement in the mammal's jaw, opening and closing, without fore and aft or lateral movement, he shows the successive changes going on coincident with the more complex movements of the jaw, and that the enamel foldings, ridges, crests, etc., have apparently been modified in conformity with the ways in which the force used in mastication was exerted.

Professor A. Hyatt,[2] in an exhaustive study of the Planorbis of Steinheim, shows among other things the effect of gravitation as accounting for the form of the mollusk-shell, citing examples from all the classes, and even drawing examples from other subkingdoms to support his views.

Professor E. D. Cope,[3] in a memoir on "Archæsthetism," considers the hypothesis of use and effort, the office of consciousness, etc. He attempts to show that consciousness is primitive and a cause of evolution. He sustains his thesis by a series of arguments which, if not beyond my grasp, would be too extensive to present here. I can only repeat the regret I expressed in the Buffalo address, namely, that neither Professor Cope nor Professor Hyatt has yet been induced to present to the public an illustrated and simple outline of their theories. Such a demonstration, I am sure, would be acceptable not only to the public but to many scientific students as well. While these two eminent naturalists believe fully in the derivative theory, they insist that Darwin's theory is inadequate to explain many of the phenomena and facts which they encounter in their studies. Darwin has distinctly said in his first edition of the "Origin of Species," "I am convinced that natural selection has been the main but not the exclusive means of modification"; and in his sixth edition of the same work, in quoting these words, he laments that he is still misunderstood on this point. The theory of acceleration and retardation of these authors is, if I understand it rightly, a very plain case of natural selection. It was inevitable that those individuals that matured the quickest were better prepared to defend themselves, were quicker in the field, were able to give their offspring an earlier start in the season, were in every way more fitted to survive than those which matured later. It is assumed that this is a law, when, to my mind, it seems the simplest result of natural selection. Instead of overriding it, it is only a conspicuous result and proof of it.

  1. "Proceedings of the Philadelphia Academy of Natural Sciences," 1878, p. 45.
  2. "American Naturalist," vol. xvi, p. 441. Also "Proceedings of the American Associated Antiquarian Society," vol. xxix, p. 527.
  3. "American Naturalist," vol. xvi, p. 454.