The law of persistence 61 The occurrence of variations 63 Application of the law of increase 76 Natural selection 77 Elimination and selection 79 Modes of natural elimination illustrated 80 Protective resemblance and mimicry 82 Selection proper illustrated 93 The effects of natural selection 95 Isolation or segregation 99 Its modes, geographical, preferential and physiological 99 Its effects 108 Utility of specific characters 110 Variations in the intensity of the struggle for existence 112 Convergence of characters 117 Modes of adaptation: Progress 119 Evolution and Revolution 120 CHAPTER V. HEREDITY AND THE ORIGIN OF VARIATIONS. Heredity in the protozoa 123 Regeneration of lost parts 124 Sexual reproduction and heredity 129 The problem of hen and egg 130 Reproductive continuity 131 Pangenesis 131 Modified pangenesis 134 Continuity of germ-plasm 138 Cellular continuity with differentiation 142 The inheritance or non-inheritance of acquired characters 146 Origin of variations on the latter view 149 Hypothesis of organic combination 150 The extrusion of the second polar cell 153 The protozoan origin of variations 156 How can the body influence the germ? 159 Is there sufficient evidence that it does? 162 Summary and conclusion 175 CHAPTER VI. ORGANIC EVOLUTION.