XI 1 



Contents 



CHAPTER V 



The Theory of Natural Selection {continued) 

 Objections to the Theory of Natural Selection . 

 Sterility between Species ..... 

 Weismann's Germinal Selection 



129 

 129 

 147 

 154 



CHAPTER VI 



Darwin's Theory of Sexual Selection . 



Sexual Selection ...... 



General Criticism of the Theory of Sexual Selection 



167 

 167 



213 



CHAPTER VII 



The Inheritance of Acquired Characters .... 222 



Lamarck's Theory . 222 



Darwin's Hypothesis of Pangenesis 233 



The Neo-Lamarckian School ....... 240 



CHAPTER VIII 



Continuous and Discontinuous Variation and Heredity 

 Continuous Variation 

 Heredity and Continuous Variation 

 Discontinuous Variation . 

 Mendel's Law .... 

 The Mutation Theory of De Vries 

 Conclusions .... 



261 

 261 

 270 

 272 

 278 

 287 

 297 



CHAPTER IX 



Evolution as the Result of External and Internal Factors 300 



The Effect of External Influences 300 



Responsive Changes in the Organism that adapt it to the New 



Environment . • • 3 X 9 



Nageli's Perfecting Principle ....... 325 



