The book is dedicated to that group of freethinkers, including d’Alembert, Diderot, Holbach, and Voltaire, who first dared to follow the consequences of a mechanistic science--incomplete as it then was--to the rules of human conduct and who thereby laid the foundation of that spirit of tolerance, justice, and gentleness which was the hope of our civilization until it was buried under the wave of homicidal emotion which has swept through the world. Diderot was singled out, since to him the words of Lord Morley are devoted, which, however, are more or less characteristic of the whole group. J. L. The Rockefeller Institute for Medical Research, _August, 1916_ CONTENTS PAGE CHAPTER I Introductory Remarks 1 CHAPTER II The Specific Difference between Living and Dead Matter and the Question of the Origin of Life 14 CHAPTER III The Chemical Basis of Genus and Species: 40 I.--The Incompatibility of Species not Closely Related 44 II.--The Chemical Basis of Genus and Species and of Species Specificity 53 CHAPTER IV Specificity in Fertilization 71 CHAPTER V Artificial Parthenogenesis 95 CHAPTER VI Determinism in the Formation of an Organism from an Egg 128 CHAPTER VII Regeneration 153 CHAPTER VIII Determination of Sex, Secondary Sexual Characters, and Sexual Instincts: I.--The Cytological Basis of Sex Determination 198 II.--The Physiological Basis of Sex Determination 214 CHAPTER IX Mendelian Heredity and its Mechanism 229 CHAPTER X Animal Instincts and Tropisms 253 CHAPTER XI The Influence of Environment 286 CHAPTER XII Adaptation to Environment 318 CHAPTER XIII Evolution 346 CHAPTER XIV Death and Dissolution of the Organism 349 Index 371 The Organism as a Whole CHAPTER I INTRODUCTORY REMARKS