Polarity, 106 Potencies, complex, 112, 120 explicit, 84 implicit, 84 primary, 84, 111 prospective, 77 ff., 83, 89, 118, 125, 241 secondary, 84, 110 Poulton, 198 Precipitin, 207 f. Pressure experiments, 63, 141 Primary potency, 84, 111 purposefulness, 146, 287 regulation, 85, 174, 188 Progress, 305 Pronuclei, 55 Prospective potency, 77 ff., 83, 89, 118, 125, 241 value, 77 f., 80, 122 Protista (Protozoa), 27, 130, 236 Protoplasm, 28, 30 morphogenetic rôle of, 67 Przibram, 112, 248 Rádl, 247 Rauber, 235 Reaction, answering, 181 Reciprocity of harmony, 156 f. Re-differentiation, 75, 111, 163 Regeneration, 55, 74, 105, 111, 221 super-, 115 f. Regulation, 68, 73, 85, 111, 165 defined, 166 metabolic, 198 f. secondary, 85, 165, 188 Reinke, 146 Restitution, 21, 74, 110, 112 ff. defined, 166 and Darwinism, 267 and Lamarckism, 286 of second order, 158 Retina, 191 Retro-differentiation, 163 f. Rhumbler, 93 Ribbert, 114 Rickert, 315 ff. Roux, 26, 48, 55 ff., 66 f., 76, 89, 92 f., 108, 161, 176 f., 241 Rubner, 193 Sachs, 117 Sadebeck, 279 *Salamandra*, 175, 281 Schneider, 146 Schultz, E., 200 Schultze, O., 67 Schwendener, 177 Science, 14, 297 natural, 1 ff. rational, 12 Sea-urchin, *see* Echinus Secondary potency, 84, 110 regulation, 85, 165, 188 Secretion, internal, 116, 200 Segmentation, 35 Selective qualities (of tissues), 186 Self-differentiation, 108 Semon, 216 f. Sex, 107 Single, the, 315 ff. Skeleton, 40 ff., 44, 47, 92 Spemann, 105 Spermatozoon (spermia), 32 ff. Splitting (of hybrids), 229 f. Stahl, 197 Standfuss, 278 Starfish, 44, 81, 122 Starling, E., 116, 204, 212 *Stentor*, 131 Stimuli, directive, 102 ff. formative, 102 ff., 113, 118, 133 of restitutions, 113 f. Structure of protoplasm, 66, 69, 72 f. 85, 88 Substance, living, 17 Sumner, 196 Super-regeneration, 115 f. Surface-tension, 91 Sutton, 230 Symmetry, 39, 68, 70, 72, 89, 98 System, combined types of, 153 ff. complex, 219 f. complex-harmonious, 155 equipotential, 120 harmonious-equipotential, 121 ff., 151 f. mixed-equipotential, 154 morphogenetic, 119 f., 163, 241 Systematics, 14 ff., 21, 243 f., 253, 264, 293, 296 Taine, 308, 310 Theology, natural, 1 ff. Thomson, J. A., 16 Thymus, 204 Thyroid, 204 Tissue, 38 Toxins, 207 f. Transformism, 251 Truth, 7 Tschermak, 228 *Tubularia*, 126 ff., 133, 158 ff. Type, 48, 247 f., 282, 291 “Understanding” (historically), 302 Universality, postulate of, 148 f. Universe, 5 Univocality, principle of, 161 “Values,” 317 ff. prospective, 77 f., 80, 122 Variation, 218, 237 f., 276 Variation, fluctuating, contingent, 264 f., 273 f., 282, 290 Vernon, 232, 238