Shark, basking, 270, 280; hammer-headed, 280; man-eating, 280. Sharks, 280. Shearwaters, 345. Sheep-fluke, 138. Sheep, Rocky Mt., *383, 397. Shipworm, 251. Shoveller, 347. Shrews, 391. Shrimp, 151, 152. Silk-worm, anatomy of, *178. Siphonophore, 98. _Siren_, 297, 298. _Sistrurus_, 322. Skate, barn-door, 281; common, 280, *281. Skates, 280. Skeleton of coral, 105. Skeletons, preparing, 452. Skink, blue tailed, *317. Skin of toad, structure of, 40. Slipper-animalcule, *35; structure and life of, 34. Slug, giant yellow, *252. Slugs, 252, 253. Snake coral, 321. Snake, garter, *320; life of, 307; structure of, 303; gopher, *322. Snake king, *321. Snakes, 316. Snails, 252, 253. Snapping-turtle, 314. Snipes, 349. Snowflakes, *358. Snow-goose, 347. Social life, 410. _Somateria_, 347. Songs of birds, 364. Sora, 349. Sound making of orthoptera, 193. Spadefoot, 300. Sparrow, English, dissection of, (facing), *327; life-history and habits of, 335; structure of, 327; western chipping, *360. Sparrow-hawk, 353. _Spatula clypeata_, 347. Species, defined, 69. Species-extinguishing, 442. Species-forming, 408, 442. _Speotyto cunicularia_, 353. _Sphinx chersis_ larva, *431. Sphinx-moth, pen-marked, larva, *431 _Sphyma_, 280. Spicules, sponge, 85. Spider and web, *237. Spider, crab, *235; jumping, *235; long-legged, *233; running, *234; running with egg-sac, *234; triangle, and web, *238. Spider-crab, 154. Spiders, 229; hunting, 233; sedentary, 233; trap-door, 233; wandering 233; web weaving, 233. Spinnerets of spider, *233. _Spizella socialis arizonæ_, *360. Sponge, commercial, 86; fresh-water, 84; glass, *87; skeleton of, 88; structure of, 88. Sponges, 84; calcareous ocean, 85; classification of, 91; development and life-history of, 89; feeding habits of, 88; form and size of, 87; of commerce, 90. Spongin, 86. _Spongilla_ sp., 84. Springtail, American, *181. Squamata, 312, 316. Squid, great, *257. Squids, 255, 257. Squirrels, 391. Starfish, *109; cross-section of, *112. Starfishes, 108, 121. _Stentor_ sp., *79. _Sterna_, 345. _Sterna maxima_, 194. Sting-ray, 281. Stone-fly, *182. _Strix pratincola_, 353. _Strongylocentrotus_ sp., structure of, 113. _Strongylocentrotus franciscanus_, *115, 122; structure of, 115. Struggle for existence, 406. _Struthio camelus_, 342. Sub-species, 69. Suckers, 283. Sucking-bugs, 197. Sun animalcule, *78. Sunfish, dwarf, 271; golden, dissection of, (facing) *263; life of, 270; structure of, 263. Supplies, obtaining laboratory, 453. Swans, 347. Swarming of honey-bee, 219. Swell-fish, 285. Swift, common, 316. Sword-fish, 285.