Nitrifying bacteria, 16 ff. Non-Mendelian inheritance, genus and species characters, 70, 151, 251; rate of segmentation, 246; first development, 247 Northrop, 366 _Nostocaceæ_, 21 Nussbaum, M., 149 Nuttall, G. H. F., 56 ff. _Ocneria dispar_, 225 _Œnotherus_, 369 Onslow, H., 249 Organ-forming substances or hormones in regeneration, 154 ff.; causing metamorphosis in tadpoles, 155-157; decidua formation, 158; development of milk glands, 158; Sachs’s theory of, 159 Organisms from eggs, 128 ff. Origin of life, 14 ff., 33 ff. Osborne, 23 Osterhout, W. J. V., 312 Ostwald, Wo., 29, 305, 312 Oudemans, 225 Overton, 123 _Palæmon_, 193 _Palæmonetas_, 193; geotropism of, 270 _Palinurus_, 193 _Pandorina_, 277 Parker, G. H., 264, 269 Parthenogenesis, artificial, 95 ff.; “spontaneous,” 107 Pasteur, 14 ff., 24, 33, 38 Patten, B., 264 ff Pauli, W., 289 Pavy, 350 Payne, F., 322 Pearl, R., 203, 244 _Penicillium_, 289 _Pennaria_, 192 Pepsin, synthetic action of, 28, 62, 63 Pfeffer, 92 ff. Phagocytosis, 367 _Planaria_, 173 ff., 177 _Planorbis_, 142 Plants, heteroplastic grafting in, 47 ff.; regeneration in, 160 ff. _Polygordius_, 280 Polymorphism, 222 _Porthesia_, 256, 280 ff. Preadaptation, 12, 324 Precipitin reaction, 54 ff. Preformation of organism in egg, 128 ff., 142-145 Presence and absence theory, 230 ff. _Primula_, 243 Proteins, specific reactions of, 54 ff.; and species specificity, 68; and evolution, 70, 348 _Protenor_, 200 ff., 208 _Proteus_, 325 ff. Przibram, H., 176 Pure lines, 333, 334 _Pycnopodia spuria_, 74 _Pyrrhocoris_, 198 Radiation pressure, rôle in transmission of spores through interstellar space, 34 ff. _Rana, esculenta_, 46; _palustris_, 46; _virescens_, 46 Rate of segmentation, a non-Mendelian hereditary character, 246 Rau, 366 Reaction, tropistic, 11 ff., 92 ff., 147, 178, 187, 255 ff.; precipitin, 54 ff.; anaphylaxis, 61 ff. Regeneration, 9 ff., 153 ff.; in plants, 160 ff.; in _Bryophyllum_, 161-167; in animals, 167 ff.; in _Tubularia_, 167-170; in _Cerianthus_, 171 ff.; in Planarians, 173-176; in _Alpheus_, 176; and autolysis, 178-181; of lens, 182, 183; external influences on, 192 ff.; of gonads in hermaphrodites, 219 Regulation, 139, 140, 141; in regeneration, _see_ Regeneration. Reichert, E. T., 64 ff. _Reseda_, 90 Resistance of spores, 36; seeds, 36 ff. Reversibility of development, in _Campanularia_, 178 ff.; in Ascidians, 180; in egg, 189 ff.; in _Antennularia_, 194 _Rhabdonema nigrovenosum_, 213 Richet, C., 61 Richter, 34 Ringer solution, 99 Robertson, T. B., 28 ff., 62 ff., 104, 311 Roentgen rays, 45 Roscoe, _see_ Bunsen Rotifers, determination of sexual cycle by food, 224