Plotheia frontalis, polymorphic, 26,29 Plusia, fixity and variation in, 26 Poephila gouldiae, variation of, 148,149 Polarity of individual, 44 Polia chi, melanic, 138 Polyanthus, short-styled selected, 236 Polydactylism in Cat, 52,53 Polyembryony, 45 Potato, variation in, 91 Poultry, evolution of, 90 Primula obconica, 91 Primula sinensis, flaked, 57 Leaf-shapes, 70 new dominant in, 92 sterility in, 236 "Giants", 236 Primula, species-hybrids, 242 Protective coloration, 140 Pyrrhulagra, local forms, 120 Python, twin-vertebrae, 60 Quiscalus, geographical races of, 156 Rabbit, Angora, 46 colours of, 93 Incompatibility with hare, 242 Raimannia odorata, Macdougal's experiments on, 226 Rats, Variation in, 248 Recessives, origin of, 90 Reciprocal crosses, giving distinct results, 105 et seq. Regeneration, 70 Repulsion, 110 Reversal on Regeneration, 77 Rhamphocoelus, geographical forms, 159,184 Rhinoptera, variation in jaws of, 38 Rhythm in repetition, 69 Ribs, variation of, 68 Rights and Lefts, 57-58 Ripples, analogous to segments, 60,66,67 regeneration of, 79 Rollers, geographical races of, 160 Ruff, polymorphism of male, 28