Photosynthesis, 70, 76, 86. Phototaxis, 144. Phyla animal, 247; morphology of, 247; relations between, 252; ancestries of, 252. Phylogenies, 253; are summaries of morphological results, 254; indicative of directions of evolution, 254; criteria of, 253. Phylogeny, 246. Phylum, 210. Physical basis of life, 84. Physico-chemical reactions, 80; are directed, 118; the means of development and behaviour in the organism, 160. Physico-psychical parallelism, 160. Physics, a statistical science, 116, 377. Physiology Galenic, 122; an analysis of organic activity, 120, 328. Plants, geological history of, 261; characterised by immobility, 277; contrasted with animals, 277. Platonic ideas, 204. Platyhelminths, morphology of, 248. Poikilothermic animals, 68. Poincaré, and Brownian movement, 119. Polar bodies, 198. Polyzoa, 164. Porifera, 248. Potential, 61. Potential energy, 58, 114. Preformation an embryological hypothesis, 128. Probability, 350. Proteids, digestion of, 90. Proto-forms, 254. Protoplasm, nature of, 106; artificial, 106; disintegration of, 107; activities of, 107; similar in plant and animal, 294. Protozoa, 247; behaviour of, 293. Pterodactyls, 274. Races (in specific groups), 194. Radiation, 355; of sun, 51; transformation of energy of, 57. Radio-activity, 56, 359. Reality, objective, 43. Reception, 3; organs of, 271; by specialised sense-organs, 11. Recessiveness, Mendelian, 196. Reflex action, 4, 272; concatenated, 150; a complex series of actions, 6; not necessarily accompanied by perception, 155; the basis of instincts, 150; a schematic description, 5; in decapitated frog, 6; frictionless cerebral activity, 8; involves a limited part of the environment, 50. Reflex arcs, 272. Regeneration, 142; in Hydra, 164; in sea-urchin embryo, 164; in Planaria, 164. Regression, 189. Reinke, and structure of protoplasm, 106. Reintegration in development, 171. Rejuvenescence, 175. Releasing agencies, 157. Reproduction, 167; asexual, 175; by brood-formation, 173; by conjugation, 173; sexual, 174; by division, 172; compared with minting machine, 242; of the tissues, 180. Responses of organisms, 217; directed, 269; of magnet, 279; of green plant, 279. Reversibility, physical, 369. Rodewald, chemical nature of protoplasm, 106. Roux, experimental embryology, 131; development the production of a visible manifoldness, 307. Saliva, secretion of, 96. Salivary glands, metabolism of, 96. Salivary secretion, not a purely mechanistic process, 112. Sea, not really rich in life, 306. Sea-urchin gastrula, 170. Secretion described mechanistically, 98. Secretion, psychical, 99. Segmentation of the ovum, 129.