Symbiosis, 155, 413. Symmetry, bilateral, 5; radial, 108. _Sympetrum illotum_, *196. _Syngnathus fuscum_, 285. Tadpole, 55. Tadpoles, *296. _Tænia solium_, 139. Tapeworm, 139. Teal, blue-winged, 347; green-winged, 347. Teleostomi, 282. Tell-tale, 349. Teredo, 251. Tern, 194. Terns, 345. Terrapin, diamond-back, 314; red-bellied, 314; yellow-bellied, 314. _Testudo_ sp., *315. _Tetragnatha_ sp., *233. _Thalarctos maritimus_, 398. _Thamnophis_ sp., life of, 307; structure of, 303. _Thamnophis parietalis_, *320. Theridiæ, 235. _Therioplectes_ sp., cornea of compound eye of, *186. Thomisidæ, 235. Thrasher, sickle-billed, *371. Thrush, russet-backed, *363. _Thymallus signifer_, 284. Ticks, 229. Tiger-beetles, 209. Toad, cellular structure of, 40; development of, 55; garden, dissection of, 5; horned, 317; skeleton of, *11. Toads, 299, 300. Torpedo, 281. Tortoise, Galapagos giant, *315. Tortoises, 313. Tortoise-shell, 315. _Totanus melanoleucus_, 349. Trachea, *184. Tree-frogs, 300. Tree-toads, 300. Trepang, 124. Trichina, 140. _Trichina spiralis_, 141, *141. Trichinosis, 141. _Triopha modesta_, *254. Tripoli rock, 82. Triton, green, 297. _Trochilus colubris_, 356; nest and eggs of, *357. Trout, rainbow, *283. Tumble bugs, 209. _Turdus ustulaius_, *363. Turkeys, wild, 350. Turtle, green, 315; hawk-bill, 315; logger-head, 315. Turtle-dove, 351. Turtles, 313. _Tympanuchus americanus_, 350. _Tyroglyphus siro_, *230. Ungulata, 393. _Unio_ sp., life-history and habits of, 243; structure of, 239. _Uria troile californica_, *344. _Ursus americanus_, 398. _Ursus horribilis_, 398. _Varanus niloticus_, 318. Variation, 406. Variety, 69. Venation of wings of insects, 174; of wings of Monarch butterfly, *175. _Venus mercenaria_, 247. Vermes, 127; life-history and habits of, 132; classification of, 135. Vertebrate, defined, 30; brains of, 376; eye of, *379. Vertebrates, 259; structure of, 259. Vespidæ, 217. Vinegar-eel, 140, *140. Viper, 324; blowing, 321. _Vipera cerasta_, 324. _Vorticella_ sp., *76. _Vorticella_, structure and life of, 75. _Vulpes pennsylvanicus_, 398. Walking-stick, 193, 194. Wapiti, *394. Wasps, 212; digger, 217; solitary, 217. Water-beetle, predaceous, 210. Water-beetles, 206. Water-boatman, *199. Water-boatmen, 197. Water-flea, 148, *149. Water-dog, 298. Water-snake, 320. Water-strider, 197, 199, *199. Water tiger, 212, *214. Weevils, 209. Whalebone, 393. Whales, 393. Wheel-animalcule, *143. Whip-poor-will, 356. Whitefish, 284. Wild-cat, 398. Wings of Monarch butterfly showing venation, *175. Wolf, 398. Woodchuck, 391. Wood-duck, 347. Wood-frog, 300.