Blood, of insects, 78. Boll weevil, 95, 96. Boll worm, 95, 96. Brain, of fish, 118. Breathing, of bird, 161; of insect, 76. Bureau of entomology, 95. Butterfly, 83. Cabbage butterfly, 84, 86, 87. Camel, 214. Candle, 5. Carbon dioxide, 24. Carp, 112, 117, 123. Cat, 184. Caterpillar, tent, 84. Cell, 6, 7. Celom, 46. Cephalopod, 106. Chelonia, 143. Chimpanzee, 219, 221. Chirping, 66. Chitin, 77. Cilia, 14, 20, 101, 103. Ciliated chamber, 17. Circulation, in amœba, 12; in insect, 77; in fish, 117. Clam, hardshell, 104; softshell, 104. Class, 9. Classification, of animals, 8, 125; of birds, 177; insects, 82; mammals, 193. Click beetle, 91. Clitellum, 43, 47. Cloaca, 18. Clothes moth, 84, 92, 93. Cockroach, 71. Cocoon, 84. Codling moth, 84, 86, 87, 95. Cœlenterata, 28. Coleoptera, 82. Collecting insects, 72. Colorado beetle, 90, 91. Coloration, warning, 84, 146; protective, 34, 37, 49. Colours of flowers, 85. Comparative study, 85, 108, 122, 223; moth and butterfly, 85. Copper head, 145. Coral, 31. Coralline, 31. Coral snake, 145, 146. Cricket, 71. Cross-fertilization, 25. Cuckoo, 179. Cuttlefish, 107. Cypræa, 104. Cysts, 13. Darwin, 48, 148. Devil’s horse, 71. De Vries, 148, 224. Digits, 222. Diptera, 82. Division of labour, 27, 29. Dog, 224. Dolphin, 209. Doodle bug, 91. Dorsal, 43. Dove, 179. Dragon fly, 93. Duckbill, 196. Ear, of bird, 151; of frog, 131; of fish, 112. Earthworm, 42. Echinoderms, 9, 34, 125. Economic importance of birds, 167; insects, 93; molluscs, 105; rodents, 206. Ectoderm, 26, 87. Ectoplasm, 11, 14. Egg, of insect, 81. Endoderm, 26, 27, 37. Endoplasm, 11, 14. Energy, in amœba, 12; organic, 2, 3; plant, 2, 3, 5. Environment, 148. Epidermis, of mussel, 98. Excretion, 12. Eye, of bird, 150; of frog, 30; of grasshopper, 67, 79; of fish, 111. Family, 8. Fangs, venomous, 145. Farmers’ bulletins, 95. Feather, 155. Fertilization, cross, 85. Field study, 10, 22, 42, 71, 72, 97, 127, 165, 166, 167, 184. Fins, 110, 113. Flagellum, 21, 27. Flatworm, 49. Flea, 92, 93. Flight, of bird, 157, 175; of moth, 84. Fly, horse, 81; house, 92, 93. Food, of birds, 177. Food tube, of bird, 163; of fish, 116; of insect, 76; of mussel, 102. Foraminifera, 15, 18. Frog, 128. Function, 1. Ganglion, 45. Gasteropod, 108. Gastrula, 7. Genus, 8. Geographical barriers, 148. Gila monster, 147. Gills, of mussel, 100; of fish, 115. Gnawing mammals, 203. Gopher, pouched, 204. Gorilla, 221. Grantia, 18. Grasshopper, 70. Gypsy moth, 95. Hands, defined, 220. Heart, insect, 77. Hemiptera, 82. Heredity, 147, 153. Hessian fly, 95. Horned toad, 140. House fly, 92, 93. Human species, 220. Hydra, 22. Hydranth, 29. Hydroid, 28, 29, 30. Hymenoptera, 82.