Fishes, distribution of, 261. Fluctuating variations, 200. Food-stuffs, absorption of, 89. Force, 354. Form, accidental and essential, 167, 353; geological, 168; crystalline, 168. Frequency distributions, 22, 187, 350. Frog, development of egg of, 131. Functionality, 343; in physical systems, 307. Galvanotropism, 145. Gases, compression of, 362; kinetic theory of, 117, 361. Gastrea-theory, 177; illustrated, 255; limitations of, 256. Genera, stability of, 186. Geometry, Cartesian, 25; Euclidean, 19, 25; perceptual and conceptual limits, 21. Geotropism, 144. Germ-cells, 175; and soma, 179. Germinal selection, 241. Germ-layers, 177; theory of, 256. Germ-plasm, a mixture, 240; stability of, 240. Givenness, 47. Gonads, 179. Growth law of, in the organism, 172; by accretion, 169; by ecdysis, 276; geometrical, 169; physical, 167; of crystals, 167; and differentiation, 170; variability of, 172. Haeckel, the Gastrea-Theorie, 177, 254. Harmonic analysis, 11. Harvey, and the circulation of the blood, 121. Heat, flow of, 117; production of, in physical changes, 114. Heliotropism, 144. Heredity, 181. Hertzian waves, 355. Homoiothermic animals, 67. Hormones, 225. Human activity, tends to arrest dissipation of energy, 312. Huxley, 84; and mechanistic biology, 127; and the physical basis of life, 113; and mechanism, 106; and universal mathematics, 215. Hybrids, Mendelian, 196; infertility of, 195; between Linnean species, 194. Hydra, regeneration of, 162. Idants, 183. Idealism founded on pure reasoning, 45; of Berkeley, 45. Ids, 183. Immunity, 35. Individual, 162; definition of, 167. Individuality, orders of, 163; physical concept of, 165; morphologically an artificial concept, 166; in societies, 171. Inertia, 354. Infinity, a definition of, 342. Inorganic happening abolishes diversity, 310. Instinct, a problem for naturalists, 283; an inheritable adaptation of behaviour, 287. Instinct and intelligence, 283; distinction not absolute, 294; may coexist, 306. Instinct and functioning, 286. Instinctive actions not necessarily unconscious, 283; not learned, 286; not necessarily perfect, 284; effective from the first, 285; capable of improvement, 285. Intelligent actions, non-inheritable adaptations of behaviour, 287; involve deliberation, 50, 287; involve conscious relations with the environment, 288; involve use of tools, 284. Intensity-factors, 61. Intensive multiplicity, 303. Irreversibility, 62. Irritability, 100. Isothermal changes, 361. James, William (and academic philosophies), 80. Jennings, and physiological states, 154; behaviour of Protozoa, 293; animal movements, 149; the avoiding reaction, 149. Katabolism, 90.