Sensory nerves, 277 



Separation layer, 91 



Septic tank, 631 



Septicemia (sep'ti se'me a), 618 



Serum (se'rwm), 187; dried, 197; antitoxic, 



237 ; reactions of, 240 ff. ; specific, 242 

 Sewage disposal, 630 ff. 

 Sex, energy needs related to, 116; determi- 

 nation of, 492 

 Sex characters, primary, 388 f. ; secondary, 



391 f. 

 Sex-linked characters, 488 f. ; in man, 500 

 Shares of nutrients, 126 f., 128 ff.; require- 

 ments in, 130; nutritive values in, 131 

 Sharks, 210 

 Sheep tick, 177 

 Shellfish, 32 



Sherman, Henry C. (1875- ), 109 

 Shoot, 11, 12 

 Shorthorn, 7 

 Shrimp, 359 



Sickness, and health, 426 ; measurement of, 

 605 f.; poverty and, 607 f., 611; and 

 ignorance, 608 f . 

 Simians (sim'iSnz), 699 

 Simpson, Joseph Y. (1811-1870), 659 

 Siphon of clam, 92, 209 

 Skeleton, 48; minerals in, 123 

 Skin, of mammals, 14; colors of, 63, 517; 

 ridges on, of fingers, 73 ; of lizard, 90 ; of 

 salamander, 90; function of, 216 f.; sec- 

 tion of, 2177- irritants of, 637 

 Skunk, 548 



Sleep, metabolism during, 114 

 Slime molds, frontispiece, 36, 687 

 Slips, 370 



Smallpox, 235 f., 237, 445 

 Snail, 92 ; balancing organ of, 288 ; fossils 



of, 454 

 Snakes, 4, 211,422, 696 

 Sneeze reflex, 288 

 Social organism, man as, 554 

 Social sensitivity, 667 

 Sociality, 56 



Sodium, 100; and heart action, 124 

 Soil, and seeds, 81 ; aeration of, 83 ; evapo- 

 ration from, 83; character of, 98, 100; 

 conservation of, 156, 645 ; fertility of, 644 

 Soma (so'mfl), 507 

 Sorting, 29 ff. 

 Sparrow, English, 589 



Specialization, 529 ff. ; in Volvox, 419 

 Species, 36 ff. ; origin of, 446 ff., 506 ff. ; re- 

 lationship of, 455 ff. 

 "Speedup", 224 



Spemann, Hans (1869-1941), 363 

 Spencer, Herbert (1820-1903), 466 

 Sperm, 376 



Spermaries, 305, 307, 377 

 Spermatophytes (spur'mo to fits'), 398 ff., 



412, 690 f. 

 Sperti, George (1900- ), 230 

 Spicules (spik'ulz), 195 

 Spiders, 693 f. 



SpiUman, W. J. (1869-1931), 480 

 Spinal cord, 275, 278, 279, 280, 294 

 Spiracles (spir'a k'lz), 16 

 Spireme, 368 

 Spirogyra, 374, 688 

 Sporangia, 375 

 Spores, 370 f., 375 

 Sporophyte, 385 

 Sporozoa, 370, 692 

 "'Sports", 496, 509 

 Sprouting of seeds, 81 ff. 

 Squash bug, 352 

 Squid, 552 



Stalk, 12; tissue of, 91 

 Stamens, 400 

 Starch, 98, 125; manufacture of, 140; test 



for, 157 ; and sugar in plant, 165 

 Starfish, 32, 228, 693 ; regeneration in, 230 



Starling, Ernest H. (1866-1927), 303 



Statocyst (stat'6 sist), 285 



Stature, variation in, 63, 69 ; inheritance of, 

 483, 484 



Stems, 11,12; tissue of, 91; types of, 145 f. ; 

 circulation through, 146 ff.; dicot, 147; 

 storage in, 180 



Stigma, 399 



Stiles, Charles W. (1867-1941), 616 



Stimuli, 284 ff.. 290 ff. 



Stock, in grafts, 369 



Stockard, Charles R. (1879-1939), 357 



Stoma (sto'mc), 141, 143, 302 



Stomach, human, 166; of fish, 173; of 

 lobster, 173 ; of cow, 174 



Stone Age, 55 



Storage, of vitamins, 132; of food, 180; in 

 plants, 215 f. 



Struggle for existence, 466, 540 ff. ; mean- 

 ing of, 544 ; patterns of, 552 f. 



717 



