Mucus, function of, in shell-fish, 114 Mud snail, behavior, 111 Multiple working hypotheses, 55 Muscidæ, Acalyptrate, 78 Museum exhibit of American birds, ecological, 145, 146 Museums, determination of specimens at, 52 relation to ecology, 22 use of ecological ideas, 145, 146 Mussels, artificial propagation of fresh-water, 114, 115 diseases, 119 eaten by _Fulgur_, 110 eaten by _Sycotypus_, 110 enemies, 119 pearly fresh-water, enemies and diseases, 119 pearly fresh-water, habits, 119 pearly fresh-water, protection, 119 reproduction of fresh-water, 114, 115 Mutation theory and ethology, 22 Mutual aid, a factor of evolution, 133 _Mya_ arenaria, growth, 114 life history, 114 Myriapods, collecting, 58 systematic literature, 71 _Nassa obsoleta_, 110 Natural conditions of existence, 96 Natural environments, 26 Natural history, 18 American lobster, 113 _Amia calva_ L., 117 Amphithoe, 113 honey-bee, 109 larvæ of Donaciinæ, 109 starfish, 115 surveys, 23, 30 Natural preserves, 34, 38 Naturalist’s Directory, 53 Nature, and nurture, 17 control, 33 Nature’s foresters, 124 Nearctic Hemiptera-Heteroptera, catalogue, 71 Nearctic spiders, 72 _Necturus_, behavior, 121 Nematocerous Diptera, aquatic, 75 aquatic, stages, 75 _Nepa apiculata_ Uhler, death-feigning, 118 Nervous system, integrative action, 98 origin of, in sponges, 116 regulatory action, 98 Nestling birds, food, 128 Nests, ants, 127 collecting birds’, 58 New Mexico, ecological distribution of animal life in, 148 insects, 148 reptiles, 148 New York, insect galls, 143 State entomologist’s reports, 74 Nomenclature, ecological, for plants, 60 phytogeographical, 22 Non-ecological surveys, 31 Normal, as ideal, 27 conditions, 27 departure from, 98 processes of nature, 26 North Carolina, oyster industry, 112 Notebook, aluminum, 44 Note slips, 37, 44 Note taking, 42, 45, 61 Noxious animals, introducing, 124 Numbering specimens, 50, 51 Numerals, 69 Nurmijärvi Lake, fauna and vegetation, 139 Nurture and nature, 17 Nutrition of Arthropods, affected by cave life, 101 Nymphs, dragon-fly, 76 Mayfly, 76 Zygoptera, keys, 76 Oak gall flies, and oak galls, 143 Oceanography, 21 Odonata, life histories, 76 transformations described, 72 Œcology, _see_ Ecology Oligochæta, 58 Ontario, Entomological Society of, index to thirty annual reports, 72 Optima, 98 development, 94 of Chætognatha, 115 physiological, 27 vital, 27, 94 Optimum, 30, 94 associational, 94 departure from, 98 vital conditions, 99 vital, in caves, 144 Orange, insects affecting the, 75 _Orchestia palustris_, habits and life history, 119