CONTENTS 



I. INTRODUCTION 1 



II. REFLEX Aeno:, 11 



III. THE TROPISMS 18 



IV. THE BEHAVIOR OF PROTOZOA . . . . ; 63 



V. INSTINCT 91 



VI. THE EVOLUTION OF INSTINCT * . 115 



VII. THE XON-INTELLIGENT MODIFICATIONS OF BEHAVIOR . . . 139 



VIII. PLEASURE, PAIN, AND THE BEGINNINGS OF INTELLIGENCE . 164 



IX. PRIMITIVE TYPES OF INTELLIGENCE IN CRUSTACEANS AND 



MOLLUSCS 180 



X. INTELLIGENCE IN INSECTS 191 



XI. INTELLIGENCE IN THE LOWER VERTEBRATES 218 



f XII. THE INTELLIGENCE OF MAMMALS 232 



XIII. THE MENTAL LIFE OF APES AND MONKEYS 260 



i 



INDEX . 283 



