Philosophy, function of, 640. _Phyciodes Tharos_ and _P. Marcia_, seasonal dimorphism of, 4; experiments with, 140. Phylogeny, conclusions from, 270; and ontogeny of Sphinx-markings, 177; of insects, 493. _Pierinæ_, seasonal dimorphism of, 13; analogous seasonal dimorphism in, 60, 108; experiments with, 122. _Pieris Napi_, experiments with, 13; summer form the younger, 29; reversion of, caused by mechanical vibration, 38; var. _Bryoniæ_, the potential winter form, 39; experiments with this var., 40; this var. the parent form of _Napi_, 41; a climatic var., 41; very variable, 43; variability due to crossing, 43; var. _æstiva_ more variable than var. _vernalis_, 43; _P. Napi_, summer and winter forms compared, 56; incongruence in this species, 457; _P. Krueperi_, seasonal dimorphism of, 78; _P. Brassicæ_, larva rejected by lizards, 337; constant in three stages, 405; photographic sensitiveness of pupa, 405; _P. Napi_, variable in two stages, 405. Plants, cultivated, 107; sterility of reverted, 596. Plastidule theory, 667. _Plebeius amyntas_ and _P. polysperchon_, seasonal dimorphism, 2; _P. Alexis_, do., 3; _P. pseudargiolus_ and _P. violacea_, do., 4; _P. agestis_, do., 50; polymorphism of females in this genus, 251. Pluvial period, 621. Polar animals, colour of, 658, 660. _Polyommatus phlæas_, distribution and climatic variation, 49; seasonal dimorphism, 50; Italian summer and winter forms compared, 55. _Polyptychus dentatus_, larva, 244. Ptarmigan, seasonal colours of, 6. _Pterogon_, larvæ of, 255; _P. ænotheræ_, larva, 256. _Pulmonifera_, functional change in lungs, 590. _Pygæra bucephala_, larva rejected by lizards, 337. Q. Quatrefages, De, spermatozoa of _Amblystoma_, 593. R. _Rana temporaria_ of Upper Engadine, 618. Ratzeburg, larva of _Anc. Pinastri_, 265. Reproduction and growth, 664. Reversion, of species, 611; two modes of, 612; periodic, 613. _Rhopalocera_, characters of, 433, 471. _Rhytina Stelleri_, extinction of, 651. Riley, C. V., descriptions of caterpillars referred to, 437, 521, 522; on sexual dimorphism in caterpillar, 535. Ring-spots, 325; development, 327; signs of distastefulness, 341; resembling berries, 344. Rösel, breeding of _Aras. Levana_ by, 6; on larva of _Deil. Euphorbiæ_, 206; of _D. Galii_, 213; of _Smer. Tiliæ_, 236; of _S. ocellatus_, 240; of _Anc. Pinastri_, 265, 268. Roux, Dr. W., struggle of parts in the organism, 689. Rutherford, D. G., colour variations of _Ater. meleagris_, 8. S. Sacc, on sterility of _Amblystoma_, 593. Salamanders, habits of Italian land species, 617; oviposition of, 630. _Salamandra atra_, experiments with, 615. _Salamandrina_, characters of, 577; _S. perspicillata_, habits of, 617.