involuntary (smooth), 131-132, 132, 193, 194- 

 195; nervous control of, 279; number in body, 

 273; in reflex arc, 278-279; tissue, 131; voluntary 

 (striated), 131, 132. 132, 193 



Mushrooms, 73, 75, 75 



Musk-ox, 540 



Mustard, 87 



Mutant, dof., 480; evening primrose, 482; fern, 499; 

 fruit fly, 480; mink, 498; rye, 480; sheep, 498; 

 tobacco, 498 



Mutation, barley, 480; and breeder, 497-499: def., 

 479; 479-481; effect of, 480; fern, 499; and evo- 

 lution, 555; fox, 499; fruit fly, 480; human, 509; 

 mink, 498; and organism studied, 480; sheep, 498; 

 tobacco, 498; and x-ray, 480 



Mutation theory, of evolution, 555, 561 



Naphthalene, 395 



Napthalene-acetic acid, 308 



Narcotic, def., 366 



National Association of Audubon Societies, 406 



Natural immunity, 316 



Natural selection, Darwin's theory, 556-559 



Neandertal man, 568-569; head of, 567; hunting, 



569 

 Nebraska, in Cenozoic period, 539 

 Nectar, 43, 48, 86 

 Needles, cedar, 82; evergreen, 81-82, 91; hemlock, 



82; pine, 82 

 Negative tropisms, def., 301; in Paramecium, 266 

 Negroid (stock), 574 

 Neolithic, def., 572 

 Nerve, auditory, 282; cell, 132, 274, 276, 277; def., 



275; fiber, 275-276; and nerve cells, 275-276; 



optic, 280; tissue, 131 

 Nerve centers, of man, 270 273; protective, 271 

 Nerve impulse, 270, 276-277; path, 275, 277, 277; 



in reflex arc, 277-279 

 Nerves, 270; earthworm, 57; man, 270; skin, 240 

 Nervous system, autonomic, 270; central, 270, 270- 



279, 279-282; involuntary, 270; of bee, 275; of 



man, 269-285; and syphilis, 332 

 Nests, ant, 46-47; bird, 25, 432; fish, 427, 427; tent 



caterpillar, 393; wasp, 263 

 Neuron, 274-279, 274; afl'erent, 278; efferent, 278; 



of human cortex, 276; intermediary, 278; motor, 



278; sensory, 278 

 Neurosis, 368 

 Newts, 31 



New Stone Age, 572-573; artifacts from, 565 

 New York City, diphtheria death rate, 330; tuber- 

 culosis, 321, 322; water supply, 345 

 New York Hospital, 369 

 Niacin, 179, 183; in common foods, 173 

 Nicotine, and insect control, 394-395; effects of, 366 

 Nicotinic acid, 179, 183 (see Niacin) 

 Nitric acid, 116 

 Nitrifying bacteria, 377 

 Nitrogen, 108, 110, 111; and bends, 233; cycle, 376- 



378 

 Nitrogen-fixing bacteria, 377-378, 377 

 Nitrogenous wastes, 237 

 Nocliluca, 64 



Nodules, def., 378; of peanut, 377 

 North America, in Paleozoic era, 534 

 Nuclear division, 456-459; in animal cell, 458; in 



plant cell, 457 

 Nuclear membrane, 107 

 Nucleolus, 107, 108 

 Nucleoplasm, 107 

 Nucleus, 106, 106, 107, 107-108, lU, 132; of egg. 



422, 423; of neuron, 275; of sperm, 423, 423; of 



white corpuscle, 208 

 Nutrient, def., 167 

 Nymph, insect, 42 



Oak, 101, 105; cork of. 153; leaf, 85; seedling, 438 



Oats, 84; breeding difficulties, 502 



Octopus, 53, 54 



Oesophagus, of earthworm, 57; of man, 188, 189, 226 



Offspring, 41-49, 352, 411-453, 455-519 



Oil glands, of skin, 240, 241-242 



Oils, 217 



Old Stone Age, 571-572; artifacts from, 575 



Olfactory lobes, of vertebrates, 273 



Olive oil, 197 



Olives, fats in, 143 



One-celled organisms (see Algae, Bacteria, Protozoa) 



Onion, ciiromosome number of, 459; experiment 

 with, 465; mitosis in root tip, 463; skin cells, 133 



Opossum, 552; reproduction, 433 



Opsonins, 316 



Optic lobes, of vertebrates, 273 



Optic nerve, in man, 280, 280 



Orange, seedless mutation, 499 



Orchids, 83, 148 



Order, in classification, 15, 99 



Organ, def., 130 



Organ system, def., 131 



Organic evolution (see Evolution) 



Organisms, behavior of, 260-309; classification of, 

 95-103; def., 3; and disease, 311-371; functioning 

 of, 137-309; heredity in, 454-519; origin of, 520- 

 579; relationships of, 373-409; and reproduction, 

 411-453; structure of, 105-135; survey of, 15-94 



Organs, bird, 21; breathing, 206-236; circulatory, 

 206-225; digestive, 188-205; earthworm, 57; ex- 

 cretory, 237-245; grasshojjper, 45; of nervous 

 system, 269-285; origin in embryo, 426; repro- 

 ductive, 421-453; structure of, 105-135; table of 

 activities, 256 



Origin, earth, 521; of species, 553-563 



Ornithology, 3 



Osmosis, 122 (see Diffusion) 



Ostrich, 22 



Outbreeding, 496-497 



Ova, 421 



Ovary, def.. 440; 421; formation of, 460; growth of 

 plant, 444; of flower, 439 



Overgrazing, and soil erosion, 403 



Overproduction, and evolution, 557; daisy, 558 



Oviducts, 422; fish, 424; frog, 422 



Ovules, def., 440; 441 



Owls, 21, 22 



Oxidation, 118-119, 121. 125, 143-144, 168; in cells, 

 120-121; chemical equation, 143; compared with 

 photosynlhesis, 143-145; and excretion, 237; 

 rapid, 118 119; slow, 118-119; and thyroid, 247 



Oxide, def., 119 



Oxygen. 108, 109, 111, 218, 219; and artificial res- 

 piration. 232-233; and breathing, 226, 231; cycle, 

 375, 376; and high alliludes, 233-234; in oxida- 

 tion, 118-119; in photosynthesis, 142 



Oxyhemoglobin, 209 



Oyster, 54 



Pi, def., 467 



Pain, and drugs, 332 



Paleolithic, def.. 571 (see Stone Age) 



Paleontology, def., 525-526 



Paleozoic era, 533, 534, 535-537 



Palisade cells, of leaves, 138, 139, 139 



610 



