Octopus, eye of, 57, 58, 348-350. _[OE]dicnemus crepitans_, 320. Ontogeny, as recapitulation of phylogeny, 98-104. Orang Outang, _see_ Apes. _Oredon Culbertsoni_, 167. Origin of Species, the, influence exercised by, on ideas of method, 1-9 _Orohippus_, 189. Otaria, eye of, 75. Ovum, 113-142; human, 120-133; amoeboid movements of young, 121-123; segmentation of, 134, 135. Owen, on ear of whale, 65; on natural selection, 333, 334. Owl, eye of, 75. P. Paddle, _see_ Whale, and _Baptanodon discus_. _Pagurus bernhardus_, 64. Pain, in relation to the theory of evolution, 417. Palæontology, 159-203; general testimony of, 156-165; testimony of, in particular cases, 165-203; consideration of objections to theory of evolution founded on grounds of, 156-165, and Appendix. _Palæotherium_, 190, 191. Paley, on natural theology, 98, 412. _Paludina_, successive forms of, 19. Panama, Isthmus of, 219. _Panniculus carnosis_, 77. _Papilio merope_, 330. Parasites, of animals, devoid of beauty, 408. Parsimony, law of, 272. Parthenogenesis, 119. Partridges, 319. Peacock, tail of, 378; courtship of, 383. Peckham, Mr. and Mrs., on courtship of spiders, 388-390. Perissodactyls, 182-192. _Petromyzon marinus_, 148. _Phenacodus primævus_, 184, 185. Phylogeny, _see_ Ontogeny. Physiological selection, 376. Pig, embryology of, 153; feet of, 176, 187; portraits of wild and domesticated, 312. Pigeons, portraits of, 298, 299; feather-footed, 359. Pilot fish, 289. _Planorbis_, transmutations of, 200, 201. Pleasure and pain, in relation to the theory of evolution, 417. _Plica semilunaris_, 75. _Pliohippus_, 189. Polar bear, skeleton of, 174; feet of, 178. Polar bodies, 125, 126. Polar star, 129. Polyps, 114. Porpoises, 24, 25, 50. Poulton, E. B., on warning colours, 325, 326; on mimicry, 331, 332; sexual selection, 400, 401, 449, 450. Poultry, portraits of, 300-302. Pronucleus, 126-128. Prophetic types, 272, 351-362. _Prophysema primordiale_, 140. Protective colouring, 317-323. _Protohippus_, 189. Protozoa, 104. Ptarmigan, 317, 318. _Pterodactyl_, wing of, 56. Purpose, Darwin's use of the word, 281, 340. Puss moth, larva of, 325, 326. Python, 66, 67. Q. Quadrumana, muscles of, 76, 82, 83; perforations of humeri of, 94, 95; hair on phalanges of, 91. R. Rabbit, embryology of, 153; multiplication of, in Australia, 286; portraits of wild and domesticated breeds of, 308; protective colouring of, 319, 320. Radiate form, beauty of, 408, 409. _Raia radiata_, and _batis_, 367-371. Rats, species of, restricted to Old and New Worlds, 212; British and Norwegian, 285, 286. Rattle-snake, tail of, 289. Recognition marks, 271-273. Religion, in relation to Darwinism, 401-418. Reproduction, different methods of, 106-117; essence of sexual, 110; foreshadowing of sexual in unicellular organisms, 115-117.