The Theory of Evolution (continued) 58 – The Evidence from Embryology 58 – – The Recapitulation Theory 58 – Conclusions 84 CHAPTER IV Darwin’s Theories of Artificial and 91 of Natural Selection – The Principle of Selection 91 – Variation and Competition in 104 Nature – The Theory of Natural Selection 116 CHAPTER V The Theory of Natural Selection 129 (continued) – Objections to the Theory of 129 Natural Selection – Sterility between Species 147 – Weismann’s Germinal Selection 154 CHAPTER VI Darwin’s Theory of Sexual Selection 167 – Sexual Selection 167 – General Criticism of the Theory 213 of Sexual Selection CHAPTER VII The Inheritance of Acquired 222 Characters – Lamarck’s Theory 222 – Darwin’s Hypothesis of Pangenesis 233 – The Neo-Lamarckian School 240 CHAPTER VIII Continuous and Discontinuous 261 Variation and Heredity – Continuous Variation 261 – Heredity and Continuous Variation 270 – Discontinuous Variation 272 – Mendel’s Law 278 – The Mutation Theory of De Vries 287 – Conclusions 297 CHAPTER IX Evolution as the Result of External 300 and Internal Factors – The Effect of External Influences 300 – Responsive Changes in the 319 Organism that adapt it to the New Environment – Nägeli’s Perfecting Principle 325 CHAPTER X The Origin of the Different Kinds 340 of Adaptations – Form and Symmetry 340 – Mutual Adaptation of Colonial 350 Forms – Degeneration 352 – Protective Coloration 357 – Sexual Dimorphism and Trimorphism 360 – Length of Life as an Adaptation 370 – Organs of Extreme Perfection 371