NDEX 



713 



rate, 608 

 Mutualism, 96, 97, 242 

 iMyelecephalon, 307, 308, 420 

 Myelinated sheath, 411 

 Myofibrils, 72 

 Myopia, 402, 613 

 Myosin, 389 

 Myxedema, 442 



N. See Haploid 



Nagana, 126 



Naiad, 244 



Nail, 368 



Nares, internal, 310, 312 



external, 305 

 Nasal chambers, 477 

 Natural Selection, Theory of, 652-656 

 Nautilus, 264, 265, 627, 644 

 Neanderthal, 355, 356 

 Neanthes, 185-188 

 Nearsightedness. See Myopia 

 Necator americaniis, 179, 180, 181 

 Negroid, 359 

 Nemathelminthes, 175 

 Nematocyst, 141, 142, 143, 144 

 Nematodes, 175, 176 



parasitic, 176, 177 

 Nemertinea, 183, 184 

 Nephridiopore, 188, 191, 192, 194 

 Nephridium, 163, 258, 259 



protonephridium, 163 

 Nephrostome, 188 

 Nereis. See Neanthes 

 Nerve, afferent, 192, 195 



efferent, 192, 195 



cranial, 307, 308, 310 



motor, 410, 411 



spinal, 309, 312 



sensory, 410, 411 

 Nerve cord, ventral, 192, 194 



dorsal tubular, 278, 280 

 Nerve impulse, 412, 414 

 Nerve net, 144 

 Nerve pathways, 418, 419 

 Nerve tissue, 74, 75 

 Nervous systems, crayfish, 216, 218 



earthworm, 192, 194 



frog, 307-312 



grasshopper, 226, 227 



hydra, 144 



man, 410-429 



planaria, 164 

 Neural canal, 380 

 Neurohumor, 428 

 Neuromuscular cells, 68, 383, 384 

 Neurons, 74, 75, 411, 412 



association, 195, 412 



motor, 195, 411, 412 



sensory, 195, 411, 412 

 Neuroptera, 221 

 Neurospora, 586 

 Neutrophil, 494 

 Neutrons, 26 



Niacin, 471, 472 



Night crawlers. See Earthworm 



Night blindness, 470 



Nitrates, 92, 93 



Nitrites, 92, 93 



Nitrogen, 485 



Nitrogen cycle, 92, 93 



Noctiluca, 123 



Node, auricular-ventricular, 500 



sinus, 500 

 Nordic, 359 



Normal frequency curve, 599 

 Nostrils, 302 

 Notochord, 280, 562 

 Nuclear membrane, 57 

 Nuclear sap, 58 

 Nucleoplasm, 58 

 Nucleoprotein, 58 

 Nucleus, 38, 57 

 Nudibranch, 264, 265 

 Nuptial pads, 299 

 Nutrition, 60 

 Nymphs, 228, 246 



Obelia, 149, 150, 158 

 Occipital lobe, 424, 425 

 Occipito-vertebral artery, 314 

 Ocellus, 224, 225 

 Octopus. See Devilfish 

 Oculomotor nerve, 307 

 Odonata, 221 

 Olfactory cells, 395 



lobe, 307, 310 



nerve, 307, 308, 309 



tract, 395 

 Oligocene (epoch), 625 

 Ommatidium, 218, 219 

 Omosternum, 305 

 Ontogeny, 560-580 

 Onychophora, 201 



Oocyte, primary and secondary, 557, 558 

 Oogenesis, 557, 558 

 Opisthobranchiata, 263 

 Opisthorchis sinensis, 167, 168 

 Opossum, 338, 340, 341, 644 

 Optic chiasma, 309, 420 

 Optic lobes, 307, 310 

 Optic nerve, 218, 219, 307 

 Oral, 270 

 Orangutan, 353 

 Order, 106, 107 

 Ordovician (period), 625 

 Organ, 75 



of Corti, 406 



systems, 75, 365-547 

 Organism, 75 

 Organized animal, 75 

 Organogeny, 567-570 

 Orrgin, muscle, 303, 304, 385 

 OrnithorJiynchis anatinus, 337, 338, 339 

 Orthogenesis, 656, 657, 658 

 Orthoptera, 221 

 Osculum, 138, 139 



