Parallels, axiom of, 157. Pascal, 219. Paul, Hermann, 69, 71. Paulhan, 90, 136. Perception, utility its mainspring, 4. Percepts, 111. Pérez, B., 36. Performing animals, 15. Perrier, E., 105. Physiologist, 119. Phonogram, 71. Photographs, composite, 10, 22. Plato, 222. Plurality, 139. Poincaré, 202. Poinsot, 146. Polymorphism, 207. Practical judgments, 93. Present, the, its nature, 160 et seq. Preyer, 33, 38, 72, 139. Progress, 219. _Quack_, 34. Quantity, measure of, 100. Quatrefages, 205, 206. Ratiocination, 25. Realism, 128. Reasoning, signification of, 23; prior to speech, 38. Réaumur, 14. Recepts, 10, 26, 89. Reflexion, 94. Regnaud, P., 71, 78, 79. Regularity, conception of, 196. Relations, 80, 81. Renan, 59, 69, 71, 76. Renouvier, 145, 146, 175, 181. Representation, 5. Representative faculty, 112. Reproduction, 207. Resemblances, 6, 90. Respiration, 166. Rhythm, 164, 165. Ribot, his observations on general ideas, 135. Riemann, 156, 158. Romanes, 10, 13, 14, 19, 34, 35, 40, 43, 46, 55, 57, 63, 66, 89, 93, 170, 184. Roots, 69 et seq., 75. Rousseau, J. J., 77. Rubicon, passage of the, 92. Sanskrit, 69. Savage languages, 95 et seq. Savage races, time-sense of, 171. Sayce, 67, 70, 73, 75, 77, 96. Schelling, 108. Schleicher, 83. Schmidkunz, 2, 3. Schneider, 7. Sciences, origin of the, 221. Scientists, 135. Scott, 43. Semi-circular canals, 149. Sensation-limits, 166. Sequence of numbers, 142 et seq. Siamese, 62. Sicard, Abbé, 44. Sidgwick, Prof., 125. Sigismund, 33. Signs, logic of, 27; imitative, 43; language of, 49; development of, 92; the importance of, 144 et seq. Sigwart, 199. Similarities, 90, 195. Simplification, 135. Skeleton, abstract thought a, 135. Smith, Adam, 31. Song, speech is derived from, 62. Space, origin of the concept of, 146 et seq.; acoustic, 148; sense of, 148; abstract notion of, 151 et seq.; _n_-dimensional, 156; Euclidean, 157; characterised, 158. Species, origin and growth of the concept of, 203 et seq.; fixity of, 205; constituent elements of the concept of, 206; defined, 206; vary in the course of evolution, 213. Specific characters, 205 et seq. Speech, origin of, 54 et seq., 59 et seq.; development of, 67. Spence, 55. Spencer, Herbert, 7, 62, 80, 137, 150, 165, 175. Stallo, 153, 158, 222. Steinthal, 59. Stern, 26. Stewart, Dugald, 31, 51. Substantive, the, 76. Substitution, 27, 110, 226. Sully, J., 25, 160, 175. Sylvester, 148. Symbolic thought, 132, 226. Symbolism, complete, 109. Symbols, 145. Taine, 33, 34, 73, 87, 129. Temporal signs, 178. Ten, the most convenient arithmetical basis, 143. Thermodynamics, 192.