CONTENTS. ix 



PAGE 



first glance apparently indifferent in character found on 

 more careful inspection to be of advantage, 166. Slight 

 characters aided by co-related differences, 167. The prin- 

 ciple of the change of function, 168. Characters of in- 

 different valus under one condition of environment, 

 .suddenly made important by a change in life-conditions, 

 169. Organs of universal character which can become 

 modified in various directions, 169. Lamarckian factors 

 called to the aid of Darwinism, 170. Answers to the 

 objection based on the improbability of the appearance of 

 the right variations at the right time for the progressive 

 perfecting or development of an organ, 170. Selection 

 directs itself according to variation, not variation accord- 

 ing to any assumed needs of selection, 171. Selection 

 works with plural variations, not single ones, 172. The 

 same selective value can often be attained through combi- 

 nations of various peculiarities and the same effect 

 reached by various means, 172. The element of chance 

 not peculiar to the Darwinian explanation of co-adap- 

 tations, 175. Answers to the objection based on the 

 assumed improbability that during the course of the 

 development of a complex organ or whole body-part, or 

 during the perfecting of a changing adaptation the 

 numerous necessary adaptations will occur in such a suc- 

 cessive series as to make possible any harmonious correla- 

 tion of the various single variations, 176. Plate's reliance 

 on the Lamarckian factor of the inheritance of characters 

 acquired through use, disuse, and other functional stimuli, 

 178. The attainment of selective value by various means, 

 178. Weismann's theory of germinal selection unaccept- 

 able, 180. Weismann's principle of amphimixis of great 

 importance, 180. The necessity of concessions admitted 

 181. The necessity of invoking auxiliary or aiding prin- 

 ciples to support the natural selection theory, 182. 



APPENDIX: Conn's discussion of selective value, 182. 

 References to papers on correlation, 184. Cope's proof 

 that natural selection cannot originate new characters, 185. 



CHAPTER VIII. 



OTHER THEORIES OF SPECIES-FORMING: THEO- 

 RIES AUXILIARY TO SELECTION . . . .187 



The presentation of theories to aid the selection theories 

 or others to replace them really a continuation of the 



