Maturation, of ovum, 46. Medulla, 199. Mesencephalon, 199. Mesenchyme, 231, 232. Mesoblast, 32. Mesoglœa, 230. Mesoshippus, 113. Metaphyta, 244. Metaplasm, 4, 5. Metazoa, 229, 230. Metencephalon, 199. Mice, 127. Microgromia socialis, 22. Microlestes, 106. Midas, 242. Mimicry, 128, 147. Mind, 216. Miohippus, 113. Misumena vatia, 142. Mitosis, 7, 25. Moles, 127, 157. Mollusca, 96, 98, 99, 100, 232, 233. Monera, 230. Monism, 208. Monkeys, Capuchin, 242. Monkeys, howling, 242. Monkeys, New World, 241. Monkeys, Old World, 241. Monkeys, primitive, 111. Monkeys, spider, 242. Monkeys, squirrel, 242. Monocotyledones, 245. Monodelphia, 233. Monotheism, 210. Monotremes, 106, 107, 239. Morula, 31. Mosses, 244. Moths, 59, 61, 102. Mountains, Appalachian, 87. Mountains, Coast Range, 89. Mountains, Colorado, 88. Mountains, Wahsatch, 88. Multituberculata, 111. Musk sheep, 151. Mycetes, 242. Myriapoda, 233. Natural Selection, 119, 120, 124, 131, 132, 134, 137, 138, 141, 143, 147, 149, 152, 153, 158, 160, 162, 165, 225. Nautiloids, 98. Nautilus, 98. Nemathelminthes, 232. Nemertina, 233. Newfoundland, 121. Nicaragua, 146. Noctiluca, 18, 230. North America, development of, 85. Notochord, 234, 235. Nucleus, 6, 41, 44, 51. Nucleus, as formative center, 8. Nucleus, hermaphroditic, 43. Nucleus, reduction of, 46. Oaks, 245. Odontornithes, 238. Olfactory lobes, 199. Optic lobes, 199. Ontogeny, 178, 179, 180. Onychophora, 233. Oösperm, 31, 173. Oösperm, segmentation of, 31. Operculum, 196. Ophidia, 238. Opponens Hallucis, 190, 191. Orangs, 243, 244. Orchis, 141, 163. Ornithodelphia, 239. Orohippus, 113. Orthoceratites, 98, 99, 100. Osteoblasts, 13. Osteoclasts, 13. Ostracoderms, 100, 101. Ova, 56. Ovum, fertilized, 180. Ovum, human, 28, 31. Ovum, maturation of, 29, 43, 46. Oyster, 234. Palms, 245. Pandorina morum, 24, 31. Pangenesis, 66, 69. Pangenesis, modified, 68, 71. Pangennæ, 6. Paramecium, 230. Parrots, 127. Parthenogenesis, 42, 59. Partridge, 134. Paupers, 223. Peacocks, 152. Pelicans, 134. Perception, 207. Perennibranchiata, 177, 238. Period, Cambrian, 85, 96. Period, Carboniferous, 85, 87, 102. Period, Cretaceous, 85, 88, 108, 110. Period, Devonian, 85, 87, 100. Period, Jurassic, 85, 88, 106, 110. Period, Ordovician, 96. Period, Permian, 104. Period, Quaternary, 85, 89, 113. Period, Silurian, 85, 87, 96, 98. Period, Tertiary, 85, 112. Period, Triassic, 85, 105, 110. Peripatus, 233. Phanerogams, 244. Pheasants, 134, 152. Phosphorescence, 20. Phrynocephalus mystaceus, 141. Phylogeny, 178, 179, 180. Pig, domesticated, 121. Pigeons, Wild Rock, 120. Pigeons, fantail, 120. Pigeons, fruit-eating, 127.