666 



INDEX 



Sex chromosomes, 429 



Sex determination, 467, 471 



Sex hormones, 471 



Sex reversal, 471 



Sexual reproduction 



invertebrates, 411 



vertebrates, 414 

 Sexual selection, 527 

 Shaler, 531 

 Shark sucker, 56 

 Shaw, G. B., 527 

 Sheep, 509, 515, 519 



effect of, grazing on trees, 20 

 Shelford, V. E., 6, 27 

 Shellfish, destruction of, 598 

 Shells, 493 

 Shin-bone, 332 

 Shrews, 534 

 Shrubs, 240, 493 

 Sight, insect, 205, 206 

 Silicon, 277 



Silurian period, 476, 513 

 Simian shelf, 551 

 Simple reflex arc, 341 

 Sinanthropus, 556 

 Siphonaptera, 102 

 Sirenia, 117 

 Skates, 423 

 Skeletal devices, 327 

 Skeletons, 234, 498 



appendicular, 329, 332 



axial, 329, 332 



for protection, 334 



for support, 333 



functions of, 333 



human, 331 



kinds of, 328 



use in movement, 334 



visceral, 329 

 Skin, 322 

 Skin color, 563 

 Skull, 329, 345 



bones of human, 330 

 Slime fungi, 71 

 Slime molds, 71 

 Sloth, 508 

 Slugs, 97, 103 

 Small intestine, 291 

 Smallpox, mS-629 

 Smell, 357, 545 

 Smiley and Gould, 611 

 Smith, Wm., 480 

 Smuts, 73, 228 



Snails, 97, 103, 328, 334, 436, 523, 531 

 Snakes, 103, 111, 490, 499, 533 

 Snake venom, antitoxin against, 634 

 Snapdragon, 239 

 Social life, 492 

 Sodium, 277 



Soft palate, 284 

 Soil, 435 



acid and alkali, effects, 15 

 Solar plexus, 354 

 Sollas, estimate of geological time by, 



553, 554 

 Soma cells, 412 

 Somatic characters, 450 

 Somatoplasm, 438, 453 

 Somatopleure, 426 

 Somites, 425 (See Metameres) 

 Space, 473 

 Spallanzani, 406 

 Spaniards, 561 

 Sparrows, 520 

 Species, 506 



concept of, 66-69 



history of, 64-69 

 Species Plantarum, 65 

 Speech, 551 

 Speman, 432 

 Sperm, 466 

 Spermary, 412 

 Spermatids, 430 

 Spermatocyte, primary, 429 

 Spermatogenesis, 428 

 Spermatogonia, 428 

 Spermatozoa, 415 

 Spermists, 467 

 Sphagnum, 73 

 Sphenisciformes, 113 

 Sphenodon, 111 

 Sphenopsida, 75 

 Sphincter, pylorus, 289 

 Spicules, 334 

 Spiders, 48, 99, 102, 103, 500, 514. 520. 



532 

 Spinal column, 329 

 Spinal cord, 341, 353 

 Spinal nerves, 353 

 Spines, 493 



Spiny-headed worm, 219 

 Spiracles, 315 



insect, 210 

 Spiral valve, 283 

 Spireme, 141, 1^3 

 Spirillum, 71, 165 

 Spirogyra, 69, 170-171 



conjugation, 170 

 Splanchnic layer, 419 

 Splanchnopleure, 426 

 Splenic fever, 622 



Sponges, 79, 103, 328, 334, 342, 491, 531 

 Spongilla, 79 



Spontaneous generation, 406 

 Sporangia, mold, 173, 174 

 Sporangiophores, 173, 174 

 Spores, 490 

 Sporocysts, 414 



