Duration, 28; duration and time illustrated, 30; illustrated by immunity, 35; more than memory, 155; a factor in responding, 155. Ecdysis, 276. Echinoderms, morphology of, 248. Ectoderm, 177. Effector organs, 158, 271. _Élan vital_, 161. Electromagnetism, 355. Electrons, 304, 355. Elimination, natural, 229. Embryological stages compared with physical phases, 308. Embryology, 127; hypotheses of, 128; physical hypotheses fail, 128; experimental, 128; suggests phylogenetic history, 213. Emulsoids, 108. Endoskeleton, 177, 276. Energetics, first law of, 51; second law of, 113. Energy, 356; available and unavailable, 55; biotic, 325; chemical, 61; and causation, 54; degradation of, 63; dissipation of, 53; electrical, 61; forms of, 325; kinetic, 52, 357; mechanical, 60, 61; potential, 53, 358; of position, 360. Energy-transformations, 54, 371; anabolic, 89; in the animal, 70; compensatory, 88; compensatory organic, 268; irreversible, 59; in physical mechanisms, 58; in the plant, 71. Engelmann, and the artificial muscle, 105. Entelechy, 161, 318; not energy, 329; is power of direction, 329; not spatial but acts into space, 330; an intensive manifoldness, 330; is arrangement, 323; involves regulations, 323; arrests inorganic happening, 327; initiates chemical happening, 327; compared with enzyme action, 327; illustrated by analogy, 322. Entropy, 54; augmentation of, 75; and Carnot engine, 369. Environment, does not select variations, 235; made by the organism, 236. Enzymes, 90; nature of, 92; pancreatic, 93; reversible, 93; activation of, 92. Enzyme activity, 93. Epigenesis in development, 129. Equilibrium, chemical, 102. false, 86, 151. Ether of space, 46, 304, 361; potential energy resides in, 361. Evolution tendencies of, 252, 264, 276, 295; separation of tendencies, 296; a transformation of intensive into extensive manifoldness, 309; a dissociation of tendencies originally coalescent, 305; increases diversity, 310; segregates energy, 311; compared with permutations and combinations, 301; a series of phases in a transforming system, 298; a logical hypothesis, 214; parallel processes in, 234; geological time inadequate for, 237; side paths in, 262; mechanistic hypotheses inadequate, 237; cosmic, 214, 297, 314; of the crust of the earth, 264. Excretory products, 269. Exoskeleton, 276. Exothermic reactions, 86. Experience and duration, 156. Experimental biology proves evolution, 246. Explosive reactions, 101. Extension in space, 18. Extinct groups, 263. Fats, digestion of, 93. Fecundity of animals, 179, 239. Ferments, 92. Fertilisation (in reproduction), 176. Finalism, 216.