Radium, poisoning by, 231 ; as occupational 



hazard, 636 

 Range of variation, 74 

 Raptores (rap to'rez), 30 

 Rats, growth of, 105 ; formulas for diet for, 

 112; appendix of, 175; and bubonic 

 plague, 625, 628 

 Recapitulation theory, 356 

 Receptacle, 406 

 Receptors, 275 ; touch, 285 

 Recessive characters, 475 ; in plants, 480 ; 



in animals, 481 ; in man, 500 

 Rectum, 167 



Redi, Francesco (1626-1697), 341 

 Reduction division, 402, 403 

 Reflexes, 262 ff., 277 ; brain and, 282 

 Regeneration, 228 ff., 370 

 Regulators, chemical, 124; vitamins as, 133 

 Reproduction, 20 ; in animals, 1 7 ; of plants, 

 17; and growth, 367 ff. ; vertebrate, 

 377 f.; of amphibians, 378; in flowering 

 plants, 398 fif. ; and heredity, 483 ff. 

 Reptiles, frontispiece, 696; breathing of, 



211 ; development of, 421 

 Resin, 215, 216 

 Respiration, and photosynthesis, 142 ; in 



roots, 202 f. ; external and internal, 208 

 Respiration calorimeter, 118, 120 

 Rest, metabolism during, 114; phvsiology 



of, 222 

 Restraints, 665 

 Retina, cells of, in insects, 15; in embrj^o, 



363 

 Rhizomes (ri'zomz), 395 

 Rhubarb, 12 

 Riboflavin, 108, 128, 132 

 Ribs, 14, 48, 206 

 Rice, polished, 104 ff. 

 Rings of tree, 581 

 Ringworm, 612 

 Rocky Mountain fever, 626 

 Rodents, 698 

 Roe, 377 



Root, 11, 12 ; hairs of, 86, 87, 142, 144 ; work 

 of, 142 f. ; structure of, 143 ff. ; storage 

 in, 180; respiration in, 202 f. 

 Rose, Mary S. (1874-1941), 128 

 Rotation of crops, 151 f. 

 Rotting, 341 

 Roundwbrms, 692 

 Roux, fimile (1853-1933), 240 



716 



Rumen (roo'men), 172 

 Ruminants, 698 

 Runners, 395 

 Rust of wheat, 544, 595 



Sacculina (sak'ti li'nc), 461 



Salamander, 38, 355 ; skin of, 90; regenera- 

 tion in, 229 



Saliva, 165 



Salts in protoplasm, 98 



Sap, circulation of, 146 ff. 



Saussure, Nicholas de (1767-18^5), 642 



Scale-lice, 581 



Scales, 90 



Scallops, ridges of, 69 



Scar tissue, 229 



Scarlet fever, 235 



Schick test, 242 



Schizophytes (skiz'6 fits), 688 



Schleiden, Matthias (1804-1881), 22 



Schwann, Theodor (1810-1832), 22 



Sciatic (si at'ik) nerve, 282 



Scion of grafts, 369 



Scurvy, 103 ff. 



Sea anemone (a nem'6 ne), 92, 382 



Sea water, modification by, 357, 360 



Seal, teeth of, 177 



Seashore, organisms of, 92 



Seasons, changes of, 89, 92; response to, 



251 ff. 

 Seaweeds, 92, 688 

 Secondary sexual characters, 314; flowers 



as, 408 f. 

 Secretin (se kre'tin), 303 

 Secretions, by glands, 169; internal, 304 ff. 

 Seedless fruit, 406 

 Seedling, 140, 144 

 Seeds, 11, 12, 400, 404 ff. ; sprouting of, 



81 ff. ; scattering of, 409 ff. 

 Segmentation of egg, 361 

 Segregation, law of, 475 f. ; Mendel's ex- 

 planation of, 485 

 Selection, natural, 466 

 Selenium (se le'ni um) poisoning, 102, 103 

 Self-pollination, 406 f. 

 Self-sufficiency, limitations of, 653 f. 

 Semicircular canals, 286 

 Semipermeable membrane, 85 

 Sensitivity, 19 f., 284 ff., 551; of animals, 



17; of plants, 17; chemical, 287 ff. ; to 



light, 289 f. 



