perature, 239-241; care of, 242; as receptor, 280; 

 and ventilation, 242 



Skull, 15, 271. 567; anteater, 193; armadillo, 193; 

 dog, 193; horse, 193; man, 193, 226 



Slime molds, 127 



Slip, def., 449; 447-449 



Slugs, 54, 55 



Small intestine, 256 



Smallpox, 325-326; cases in U.S., 325-326; epidemic, 

 325-326, 343; immunity, 316; and culture, 340 



Smell, 280 



Smooth (involuntary) muscle, 129, 131, 132, 193, 

 194, 216 



Snails, 40, 53, 54, 54; fossil series, 543; in balanced 

 aquarium, 378-379 



Snakes, 27, 29; poisonous, 27-28; shedding skin, 28, 

 29; sperm, 423; x-ray, 28 



Snapping turtle, 30; hatching, 429 



Soaring, of birds, 21 



Social insects, 46-49, 47, 48 



Sodium, 109; chloride, 109 



Soil, 148 150, 149, bacteria, 376, 377-378; conserva- 

 tion of, 403-405; destruction of, 402-403, 404; 

 erosion, 403; experiment, 137; formation of, 521- 

 523; minerals, 148-150; particles, 150; and tet- 

 anus, 330-331; top, 402, 403; and transpiration, 

 159-160; water in, 150 151 



Soldiers, variation in, 487 



Soluble, 123-124 



Somatic, def., 455 



Somatoplasm, and acquired characters, 487-490; 

 def., 455 



Sore throat, and milk supply, 345 



Sorghum, 476 



Sound and hearing, 282 



Soviet Union, and conservation, 405-406 



Soybean, and selection, 494; uses of, 494 



Spanish moss, 137, 138 



Spawning, 34; def., 424 



Species, causes of variation, 473-474; chromosome 

 number, 459; def., 15, 495-496; 97; origin of. 521- 

 579; and variety, 49.5-496 



Specific antibodies, 316 



Speech, aid to learning, 396 



Sperm, 421, 422, 423; ducts, 422; in fertilization, 

 424, 428, 429-430, 432, 442-443, 446, 447, 461- 

 462; fish, 423; flowering plant, 442, 442; frog, 423; 

 human, 423; maturation, 460-461, 461; snake, 

 423; worm, 423 



Spermary, 421; frog, 422; formation of, 460 



Spermatophytes, 72, 80-90, 81; classification of, 91 



Sphagnum, 78 



Spiders, 41, 41, 50-51; instinctive, 263-264; trap- 

 door, 51; webs, 51 



Spinal column, 271 



Spinal cord, 270-272; in man, 226, 270, 271; in 

 reflex arc, 277-279; in sheep, 271; in vertebrates, 

 273 



Spiracles, of grasshopper, 45 



Spirilla, 312 



Spirogyra, 73, 73, 74; conjugation in, 416; reproduc- 

 tion of, 415-416 



Spleen, 209-210, 222 



"Splints," of horse's leg, 542 



Sponge, 61, freshwater, 40; mus<lc cells, 129 



Spongy cells, of leaves, 138, 139, 139 



Spontaneous f^eneration, def., 411; experiments, 



411-412 

 Sporangium, bread mold, 415; moss, 447 

 Spores, bacteria, 314-315, 330; bread mold, 414; 

 def., 414; malarial protozoan, 350-351 , 350; moss. 



447; pulTball, 557; reproduction by, 414-415, 407; 

 tetanus, 330-331 



Spore cases, fern, 415; mold, 414, 415; moss, 447 



Sporulation, def., 414; 414-415, 417; in various 

 organisms, 415 



Spraying, and apples, 395; and germs, 348 



Sprouting seeds, 150, 438 



Squash, heredity of shape, 469; tendrils, 302 



Squid, 55 



Squirrel, gray, classification of, 100 



Staining, bacteria, 314, 321; cells, 458-459 



Stamens, 439, 439, 441-442, 445, 464 



Stamina te, def., 440; flower, 440 



Stanley, W. M., and viruses, 340 



Starch grains, 143 



Starches, 110, 112; chemical formula of, 141; in diet, 

 174; in diffusion, 124; digestion in plants, 158; 

 plant sources of, 141; production in plants, 140- 

 142; test for, 116 



Starfish, 40, 56, 56; chromosome number, 459 



Statistics, def., 343 



Stems. 153 160, 154, 155, 156, 157; bamboo, 157; 

 chlorophyll in, 139; conducting cells, 155; corn, 

 157; diagram, 163; growth of, 154-157; monocot, 

 157; palm, 157; structure of, 153-154; unequal 

 growth in, 303-304; variations in, 157; white 

 potato, 449 



Sterile, def., 313, 501 



Sterilization, methods, 313; and surgery, 331-332 



Sterilization of human being, 513 



Stickleback, male at nest, 427 



Stigma, 437, 440, 441, 442, 443, 443, 444 



Stimulant, 367 



Stimulus, def., 261; 263, 265, 266, 269, 270; plant 

 responses, 301-306, 301, 302, 303, 305, 306; in 

 reflex arc, 277-278, 278; responses of protozoa, 

 26.5-266, 266, 269; varies responses, 287 



Stock, in grafting. 502, 503; races of man, 573-575 



Stomach, 188, 189, 195, 197; digestion in, 193-196; 

 function, 130; glands, 191; lining, 191; move- 

 ments, 195-196; muscles, 195; structure, 194-195, 

 195; tissues, 194-195 



Stomach poisons, for insects, 393-394 



Stoma ta, 138-139; 139, 140, 159; number, 139; of 

 stems, 153 



Stone Age, artifacts from, 595; history of, 565-573 



Strain, def., 495; bacteria, 338; i)lus and minus in 

 reproduction, 417 



Strata, rock, def., 523, 523, 524, 529 



Strawberry, 86; and selection, 494; vegetative re- 

 production, 448, 449 



Streptococcus, of pus, 312; and sulfa drugs, 333, 334 



Streptomycin, 334 



Striated muscle, 131, 132, 193 (see Voluntai. 

 muscle) 



Structure, def., 3 



Struggle for existence, and evolution, 557 



Style,^^J9, 440 



Successful reproduction, 434 



Sugars, 110, 112, 208; in diet, 174; and diffusion, 

 121-124. 122, 123; and insulin. 250-252; in photo- 

 synthesis, 141-142; and metabolism, 143-144. 145. 

 190, 196, 199; movement in plants, 158; sources 

 of, 141; test for simple, 116 



Sugar cane, 84, 85; breeding of, 501 



Sulfa drugs, 333-334 



Sulfur, 108, 110, HI; "showers," 441 



Sulphuric acid, 110 



Sun, and gene action, 490; and photosynthesis, 142 



Sunburn, 242 

 Sundew, 304-305, 306 



614 



