bryo, 538; muscle, 214; structure of, 213-214, 

 213; valves of, 220; work of, 213, 218, 219, 220 



Heart failure, and adrenin, 253 



Heartwood, 156 



Heat, different from temperature, 168; form of 

 energy, 119, 168-169; loss from body, 241; unit 

 of, 169 



Heath hen, extinction of, 405 



Heidelberg man, 568 



Hemlock, 82 



Hemoglobin, 209, 231; and resemblances, 550 



Hemophilia, def., 473; heredity of, 473 



Hemorrhage, cerebral, 217 



Hemp, 89, 383 



Hepatica, 407 



Herbs, def., 80; and disease, 332 



Heredity, 454-519; and acquired characters, 488- 

 490; and breeding, 493-507: diagram of simple 

 case, 467; in dihybrids, 470-472; and disease, 370; 

 of disease in man, 510; and environment, 485- 

 491; and gene theory, 464-484; and improve- 

 ment of man, 508-519; in man, 508-519; mental 

 traits in man, 511-512; and organisms studied, 

 470; and reproduction, 454-463; of sex, 472-473; 

 sex-linked, 473; and variation, 485-491 



Herelle, d' Felix H., and bacteriophage, 340-341 



Herring, 33 



Hessian fly, 44 



Hibernation, 26 



Hickory, leaf, 85 



Hilum, def., 451 



Himalayas, 538 



Hippopotamus, and young, 461 



Hobbies, 8, 9 



Hog (see Pig) 



Hog-nosed snake, 29 



Homo heidelbergensis, 568; neanderthalensis, 568- 

 569; rhodesiensis, 568; sapiens, 569-571 



Honeybee, 48-49, 48 



Honeycomb, of bees, 48, 141 



Honeydew, ant food, 47 



Hooke, Robert, 105, 125 



Hookworm, 40, 57; disease, 354 



Hormones, def., 200; 208, 246-258; and growth, 

 303-304; and plant reproduction, 450; and sec- 

 ondary sex characters, 422; sex, 255 



Hornlessness, in cattle, 484, 497-499 



Horse, and antitoxin, 328-329; and bacteria, 374; 

 bleeding for antitoxin, 329; breeding of, 493; and 

 colts, 410; fossil history, 542-543; leg bones, 542; 

 skeleton, 541; skull, 193; teeth, 193; and tetanus, 

 330-331; thoroughbred, 493; wild, 493 



Horse chestnut twig, 155 



Horsetails, 80, 91 



Host, def., 311; 316, 320 



Housefly, 44, 348; chromosome number of, 459 



Howard, L. O., and insect menace, 391 



Human, brain, 271; gametes, 423; history, 564-573; 

 races, 573-577 



Humus, def., 399; 150 



Hundred-legger, 41, 41 



Hunger, cause of, 280 



Huntington's chorea, 510 



Huxley, Thomas Henry, 126 



Hybrid, def., 466; vigor, 496-497, 497 



Hybridization, def., 499; animal, 499-501; in cattle, 

 500; plant, 501-502; used by breeders, 499-501 



Hydra, 59; egg, 423; green, 380 



Hydrochloric acid, 194; of stomach, 194, 196, 315 



Hydrogen, 108, 109, 111; cycle, 375, 376, 377 



Hydrophobia (see Rabies), 324 



Hydrotropism, 302 

 Hypha, 414, 414 

 Hypocotyl, 451 



Ice, river of (glacier), 522; sheets, 539-540, 540 



Ichneumon fly, and adaptation, 561 



Identical twins, 514-515, 514 



Igneous rock, 521 



Immune serum, and disease, 331 



Immunity, acquired, 316; active, 326-327; to an- 

 thrax, 324; to chicken cholera, 323-324; to 

 measles, 327; natural, 316; passive, acquired, 328- 

 329; to rabies, 324-325; to scarlet fever, 327; to 

 smallpox, 325-326; to typhoid, 326-327; to 

 whooping cough, 327 



Impetigo, 243 



Impulse, in nerve, 270, 276-277 



Inbreeding, def., 496 



Incisor, 203, 203 



Incomplete dominance, def., 468 



Incomplete metamorphosis, 42 



Incubator, 313 



Independent assortment, 470-472 



Indians, and food preservation, 384 



Indol-acetic acid, 308 



Indol-butyric acid, 308 



Industrial absence, 362-364 



Industrial revolution, and tuberculosis, 321-322 



Infant care, 369-370 



Infantile paralysis, 230, 340; and carriers, 347 



Infectious disease, new problems, 338-342 



Influenza, 328, 340; epidemic, 343; immunity, 316; 

 virus, 339, 339 



Inhaling, 228-230, 228 



Inheritance of variations, and evolution, 558 



Inner ear, 281-282, 281 



Inoculation, for immunity, 323—325, 327—329, 331 



Insanity, 368 



Insect-eating plants, 306 



Insects, 41-50; as allies, 396; classification, 40, 41, 

 65; communities, 46-49; control, 391-397: cost 

 of damage, 391; as disease carriers, 348-349; eco- 

 nomic efl'ects, 389-391; importations, 396-397; 

 in insect control, 396; life cycle of, 41-42, 42, 

 43, 47; and man, 389-398; mouth parts, 43, 43, 

 45, 68; noises, 49-50; number of, 39; origin of 

 problem, 389; parental care, 430; repellents, 395; 

 scale, 46; scaly winged, 43-44; social, 46-49; 

 stomach poisons, 393-394; structure, 41, 44, 45; 

 usefulness of spraying, 395 



Insoluble substances, def., 123-124 



Instinct, 263-265; shown by wasp, 263 



Instinctive behavior, def., 263; 263-265 



Insulin, 250-252; injection of, 251 



Intelligence, def., 510; of identical twins, 515; tests, 

 510 



Intelligence quotient, def., 510, 511; graph, 511 



Intercellular material, 130, 130, 132 



Intermediary neuron, 278 



Intermediate products, of digestion, 190 



Internal secretions (hormones), 246-258 



Intestinal, glands, 191, 196, 198; juice, 196 



Intestine, absorption in small, 197-198; digestion 

 in small, 196-197; of earthworm, 57; large, 188, 

 198; of man, 189; small, 188, 195 



Invertebrates, def., 15; 39-71; examples of, 40, 64; 

 jointed legged, 41-53; number of, 39; soft-bodied, 

 53-55; spiny skinned, 55-56; table of classifica- 

 tion, 65-66 



Involuntary muscle, 129, 131-132. 132; of air pas- 

 sages, 228 



607 



