Hereditary Mass, 41, 43, 44, 46, 51. Hereditary Mass, reduction of, 46. Hereditary Threads, 31, 41. Hereditary Units, ancestral, 43, 45. Hereditary Units, maternal, 42. Hereditary Units, paternal, 42. Heredity, xiii. 39, 53, 54, 72, 73, 74, 75, 76. Heredity, examples of, 40. Heritages, atavistic, 49. Heritages, augmentation of, 47. Heritages, blending of, 47. Heritages, latent, 49. Heritages, mutually exclusive, 47. Heritages, prepotency of, 47. Heritages, struggle of, 48. Heritages, totality of, 75. Herons, 134. Hesperornis, 238. Hippopotamus, 111. Hog, 111. Holocephali, 236. Holothuroidea, 232. Hominidæ, 242, 243. Homo delinquens, 52. Homo sapiens, 52. Honey-suckers, 148. Horse, 112, 121, 122. Horse, feet of, 113. Horse, swiftness of, 122. Horsetails, 100, 102, 244. Hyaloplasm, 5. Hydra, 231. Hydroids, 231. Hydrozoa, 231. Hylobatinæ, 244. Hylobates, 243, 244. Hypoblast, 32. Hyracoidea, 239. Ichthyornis, 238. Ichthyosauria, 107, 238. Idioblasts, 6. India, 141. Infancy, 217, 218. Infant, grasping power of, 192. Infection, congenital bacterial, 53. Infection, prenatal, 54. Infusoria, 42, 230. Insecta, 233. Insectivora, 107, 239. Insects, 100, 102, 110, 135, 137, 141, 143, 144, 147, 161, 162, 163, 164, 165. Insect selection, 160, 164. Invertebrates, 96, 234. Irish elk, 114. Isolation, geographical, 166. Isolation, sexual, 166. Java, 140, 142. Jukes, the, 41. Kaffir Boom, 130. Kallima, 139, 140. Kerivoula picta, 130. Labyrinthodonts, 103, 104. Lacertilia, 238. Lagena, 13, 23. Lamellibranchiata, 234. Lampreys, 101. Lampshells, 96, 232. Lancelet, 235. Larva, of Georgia butterfly, 138. Law of battle, 158, 159. Leaf-hoppers, 141. Leaf insects, 140. Leaf thrushes, 127. Leeches, 233. Lemuroidea, 111, 240. Lepidosiren, 237. Lepidosteus, 236. Leptocardii, 234, 235. Lichens, 244. Life-forms, transmutations of, 93. Life-forms, typical animal, 95. Limestone, 13. Lions, 127, 160. Lislet-Geoffrey, 48. Liverworts, 244. Lizards, 144, 146, 158. Locusts, palatable, 146. Locusts, unpalatable, 146. Longicornia, 147. Lung-fishes, 103, 104, 237. Macacus, 243. Macaques, 243. Magnolias, 111. Malay Archipelago, 148. Mammalia, 23, 240. Mammals, 96, 107, 109, 111, 113, 144, 152, 160. Mammals, Age of, 111. Mammals, land, 165. Mammals, placental, 239. Mammals, reptilian, 106, 107, 111. Mammals, snake-eating, 147, 149. Man, 146, 216. Man, age of, 114. Man, ancestors of, 185, 186. Man, brutish instincts of, 219. Man, evolution of, 180, 188. Man, imperfect adaptations of, 190. Man, primitive, 187. Man, quaternary, 114. Mantis, 141. Marmosets, 242. Marsipobranchii, 234, 235. Marsupials, 106, 107, 239. Mastodon, 114.