T. H. MORGAN _July, 1916_ * * * * * TABLE OF CONTENTS CHAPTER I A REVALUATION OF THE EVIDENCE ON WHICH THE THEORY OF EVOLUTION WAS BASED PAGE PREFACE v 1. THREE KINDS OF EVOLUTION 1-7 2. THE EVIDENCE FOR ORGANIC EVOLUTION 7-27 a. The Evidence from Comparative Anatomy 7-14 b. The Evidence from Embryology 14-23 c. The Evidence from Paleontology 24-27 3. THE FOUR GREAT HISTORICAL SPECULATIONS 27-39 a. The Environment 27-31 Geoffroy St. Hilaire b. Use and Disuse 31-34 From Lamarck to Weismann c. The Unfolding Principle 34-36 Nägeli and Bateson d. Natural Selection 36-39 Darwin CHAPTER II THE BEARING OF MENDEL'S DISCOVERY ON THE ORIGIN OF HEREDITY CHARACTERS 1. Mendel's First Discovery--Segregation 41-52 2. Mendel's Second Discovery--Independent Assortment 52-59 3. The Characters of Wild Animals and Plants Follow the Same Laws of Inheritance as do the Characters of Domesticated Animals and Plants 59-84 a. Sexual Dimorphism 61-64 Eosin eye color of Drosophila 61-62 Color of the Clover Butterfly, Colias philodice 62-63 Color of Papilio turnus 63 Color pattern of Papilio polytes 63-64 b. Duplication of parts 65-66 Thorax of Drosophila 65 Legs of Drosophila 65-66 c. Loss of characters 66-68 "Eyeless" of Drosophila 66-67 Vestigial wings of Drosophila 67 Bar eye of Drosophila 67-68 d. Small changes of characters 68-70 "Speck" 68 Bristles of "club" 70 e. Manifold effects of same factor 71 f. Constant but trivial effects may be the product of factors having other vital aspect 73 g. Sex-linked inheritance 75-80 in Drosophila ampelophila 75-76 in the wild species D. repleta 76 in man 77 in domesticated Fowls 77-78