xii Contents 
CHAPTER V 
THE THEORY OF NATURAL SELECTION (continued) 
Objections to the Theory of Natural Selection . 
Sterility between Species 
Weismann’s Germinal Selection 
CHAPTER VI 
DarRwIn’s THEORY OF SEXUAL SELECTION 
Sexual Selection 
General Criticism of the Theory of Sexual Selection . 
CHAPTER VII 
THE INHERITANCE OF ACQUIRED CHARACTERS . 
Lamarck’s Theory . : 5 ; a . 
Darwin’s Hypothesis of Pangenesis . : . 
The Neo-Lamarckian School . i % . 
CHAPTER VIII 
CONTINUOUS AND DISCONTINUOUS VARIATION AND HEREDITY 
Continuous Variation 
Heredity and Continuous Variation 
Discontinuous Variation 
Mendel’s Law . 7 5 ‘ P ‘ i 
w The Mutation Theory of De Vries. . é 
Conclusions : ‘ i F ‘ é A 
CHAPTER IX 
EVOLUTION AS THE RESULT OF EXTERNAL AND INTERNAL FACTORS 
The Effect of External Influences 
Responsive Changes in the Organism that adapt it to the New 
Environment . 
Nageli’s Perfecting Principle 
PAGE 
129 
129 
147 
154 
167 
213 
222 
222 
233 
240 
261 
261 
270 
272 
278 
287 
297 
300 
300 
319 
325 
