I have to thank many kind friends for incidental help. Thanks are also due to Professor Flower, who courteously gave permission that some of the exhibits in our great national collection in Cromwell Road might be photographed and reproduced; and to Messrs. Longmans for the use of two or three illustrations from my text-book of "Animal Biology." C. LLOYD MORGAN. UNIVERSITY COLLEGE, BRISTOL, October, 1890. CONTENTS. CHAPTER I. THE NATURE OF ANIMAL LIFE. PAGE The characteristics of animals 2 The relation of animals to food-stuffs 15 The relation of animals to the atmosphere 15 The relation of animals to energy 16 CHAPTER II. THE PROCESS OF LIFE. Illustration from respiration 21 Illustration from nutrition 25 The utilization of the materials incorporated 27 The analogy of a gas-engine. Explosive metabolism 30 CHAPTER III. REPRODUCTION AND DEVELOPMENT. Reproduction in the protozoa 37 Fission in the metazoa 41 The regeneration of lost parts 41 Reproduction by budding 42 Sexual reproduction 42 Illustration of development 51 Parental sacrifice 56 The law of increase 58 CHAPTER IV. VARIATION AND NATURAL SELECTION.