Factors, primary, secondary, 110; three kinds, 111; congenital, 113. Falls of St. Anthony, 86. Fishes, lowest among common vertebrates, 46; trunk-fish, cow-fish, puff-fish, mouse-fish, flounder, 46; most primitive backboned animals, 92; 94; 157; embryos of, 171. Fiske, 139. Flies, may, 259. Flounder, a variant of the fish theme, 66. Fossilization, conditions of, 77-78. Fossils, 73-105; remains of, 73; groups, 77; 78, 79; order of succession, 91; oldest rocks devoid of, 92; forms, 99. Fowl, game cock, 138; pigeons, 138. Frog, 45; eggs of, larva, development of, 58, 59, 60, 68. Galapagos Islands, 102, 103, 104. Galton, 142, 147; heredity of mental qualities, 232. Gametes, 252. Gastrula, 68. Gemmules, 143. Genera, 32. Generation, spontaneous, 78. Geographical distribution, 32. Geological agencies, rain, rivers, glaciers, 88; construction, volcanoes, 88. Geology, data of, 83, 84. Germ, Bonnet's idea of, 70; cells, 144, 146; plasm, 145, 146. Gibbon, 163. Gills, 58, 62. Gill-slits, bars, clefts, 61, 62, 64; in embryos of lizards, birds, mammals, 69; 171. Giraffe, 133. Glaciers, alterations made by, 87. Goats, 157. Gorilla, 163, 165, 195. Grand Canon of the Colorado, 85, 90. Gravitation, 155. Guinea-pigs, Brown-Sequard's, 148. Gulick, 103. Haeckel, 63, 71, 184. Haemoglobin, 22. Hapalidae, 160. Harvey, 70. Hawaiian Islands, 103; snails of, 104. Heredity, 142; a real human process, 175; instinct determined by, 206; Anglo-Saxon, 213; of mental qualities, 232. Heron, 44. Hesperornis, 99. Hippopotamus, 42. Hominidae, 160. Homo sapiens, 183. Hoofed animals, 95, 96, 97. Hornets, communities of, larvae of, 260. Horse, 41, 42, 65; place of in zooelogical science, 95, 96; development of, 97; perfection of one type of, 136, 157; 167; intelligence of, 209. House-fly, eggs of, 67. Human faculty, 212; its three constituents, 212. Huxley, 6, 26, 30, 63, 184. Hydra, 50, 51, 52, 53, 68, 69; comparative study of, 204, 205, 206; 254; cells of, 255; 256, 257, 258, 261, 262, 263, 265, 266. Hydrogen, 25, 27. Hyracotherium, 96. Ichthyornis, 99. Ichthyosaurus, 94. Indians, American, pictography of, 223, 224; of Brazil, 227; life of, 272. Individual development, a resume of history of species, 63. Inertia, 155. Infant, human, activities of, 216. Ingestive structures, 17. Inheritance, 110, 131; biological laws of, 142; paternal and maternal basis of, 144; 145; Mendelian phenomena of, 146; Galton's Law of, 147; laws of, in mental phenomena, 203; strength of, in mental traits, 232; physical, provides mechanism of intellect, 233. Insects, butterflies, beetles, bees, grasshoppers, spiders, scorpions, 49; 66; eggs of common house-fly, 67; 82; nervous mechanism of, 205; communities of, 207, 258-260, 267; nervous system of, 256, 257.