Electric organs, 365-373. Elephant, foot of, 185, 186; rate of propagation of, 261, 262. Elk, 196-198, 199. Embryo, human, _see_ Man. Embryogeny, _see_ Ontogeny. Embryology, 98-155. Embryos, comparative series of, 152, 153. _Encyclopædia Britannica_, eighth ed., on instinct, 289-291. Encystation of Protozoa, 115. Endoderm, 137-142. Equatorial plate, 129. _Equus_, _see_ Horse. _Erythrolamprus venustissimus_, 330. Evolution, organic, fact of, Section I; Method of, Section II; ideas upon, prior to Darwin, 253-258; divergent, 266, 267. Ewart, Professor Cossar, on electric organ of skate, 364, 367. Existence, _see_ Struggle for. Eye, of octopus, 57, 58, 347-350; absence of, in dark cave animals, 70-72; nictitating membrane of, 74, 75; development of, from cutaneous nerve-ending, 352-354. F. Feet, 51-59, 66, 77-80, 174-192, 197. Fertilization of ova, 127, 128; of flowers by insects, 406. Fish, embryology of, 143-155; palæontology of, 163, 165, 169-171; brain of, 194-197; distribution of, 224-246; flying, 355. Fission, reproduction by, 106, 107. Flat fish, 317. Float, _see_ Swim-bladder. Flowers, fertilization of, by insects, 406. Fly, imitating a wasp, 329. Flying-fish, and squirrels, 355. _Foraminifera_, 346. Forbes, H. O., on scapulo-coracoid bones of _Dinornis_, 60. Fortuitous, Darwin's use of the word, 340. Fossils, _see_ Palæontology. Frogs, 317. G. Galapagos Islands, 227-231, 236, 237. _Galeus_, eye of, 75. Galls, vegetable, 293-295, 446-448. Gastræa, 137-140. _Gastrophysema_, 138. Gastrulation, 137, 140. Gegenbaur, 147, 181. Gemmation, reproduction by, 106, 107, 110, 111. Generalization, 5. Generalized types, 33. Genesis, classification of organic nature in, 23. Genial tubercle, 96. Geographical distribution, 204-248; _see_ Glacial period, Barriers Transport of organisms, Oceanic islands, &c. Geology, record of imperfect, 156-160, and Appendix; _see_ Palæontology. Germs, prophetic, 272, 351-362. Gesner, on classification, 24; on canaries, 313. Gill-arches, 146, 147, 150, 151. Gill-slits, 146, 147, 150-153. Gills, of young salamanders, 102; origin of, in embryo, 144; of fish, 150, 152. Giraffe, neck of, in relation to Lamarck's theory, 254. Glacial periods, effects of, on distribution of plants and animals, 209, 210, and Appendix. Goose, Frizzled, portrait of, 304. Gorilla, _see_ Apes. Gray, Professor Asa, 337 Great-toe, in man and apes, 79-81. Grouse, 317-319 Growth, correlation of, 357, 362. _Gymnotus_, 365, 367. H. Häckel, on analogy between species and languages, 32; on reproduction as discontinuous growth, 105, 106; his ideal primitive vertebrate, 143, 144. Hair, vestigial characters of, in man, 89-92. Hales, 3. Haller, 3. Hamilton, Sir William, 272. Hands, 51-55, 66, 80-82, 174-192. Hare, 318, 319. Hartmann, on flattening of early human tibiæ, 96. Harvey, on Lord Bacon's writings, 2. Heart, development of, 154.