104 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* 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, f in an exhaustive study of the Planorbis of 

 Steinheim, shows among other things the eflfect of gravitation as ac- 

 counting 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, J in a memoir on " Archacsthetism," considers 

 the hypothesis of use and effort, the office of consciousness, etc. He 

 attempts to show that consciousness is primitive and a cause of evolu- 

 tion. He sustains his thesis by a series of arguments which, if not 

 beyond my grasp, would be too extensive to pi'esent 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 dis- 

 tinctly said in his first edition of the " Origin of Species," " I am con- 

 vinced 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 as- 

 sumed that this is a law, when, to my mind, it seems the simplest re- 

 sult of natural selection. Instead of overriding it, it is only a con- 

 spicuous result and proof of it. 



* " Proceedings of the Philadelphia Academy of Natural Sciences," 18T8, p. 45. 

 f " American Naturalist," vol. xvi, p. 441. Also "Proceedings of the American 

 Associated Antiquarian Society," vol. xxix, p. 527. 

 X "American Naturalist," vol. xvi, p. 454. 



