420 



I'RINCIPLES OF ANIMAL BIOLOGY 



Nervoufs tissue, 81, 85 



Nests, 186, 187 



Neural arch, 91 



Neural canal, 91 



Neural crest, 205, 209, 212 



Neural folds, 207, 208, 209, 212 



Neural groove, 209 



Neural spine, 91 



Neurilemma, 143, 148 



Neuromuscular cells, in Hydra, 72 



Neuron, 143, 144 



Neutron, 31 



Niacin, 111 



Nicotinic acid. 111 



Nomenclature, rules of, 249 



Nostril, 214 



Notochord, 205, 208, 209, 210, 212 



as an organizer, 219 

 Nuclear membrane, 25, 26 

 Nuclear sap, 26 

 Nucleolus, 26 

 Nucleus, 23, 26 



membrane of, 25 



reconstruction of, 59, 60, 61 



shape of, 25 

 Nutrition, cause of structural change, 288 



dependence of animals on plants for, 

 287 



in ecological relations, 287-288 



Order, 245, 248 



Ordovician, 330, 332, 335 



Organ, 85 



Organic compounds, 40-42 



Organismal theory, 66, 74 



Organizers, 219, 220 



Origin, of muscle, 94 



"Origin of Species," 18 



Ornithologist, 257 



Orthocone, suture of, 343 



Osculum, 261 



Osmosis, 43, 44 



Ostracoderms, 332 



dtozoa, 247 



Ovary, 153, 156, 157, 177, 178, 179, 183 



of earthworm, 168 



of Hydra, 72 

 Oviduct, 177, 178, 179, 183 



of earthworm, 168 

 Oviparous, 183, 185 

 Ovisac, of earthworm, 168 

 Ovoviviparous, 183-185 

 Ovum, 160 

 Oxidation, 37 



as source of energy, 48, 49 

 Oxygen, atom of, 32, 33 



mechanism of collection of, 118 



molecule of, 33 



O 



Obelia, reproduction of, 173, 175 

 Ocean currents, 301, 303 

 Oenothera, mutation in, 354, 355 

 Offspring, care of, 189, 190 

 Oken, Lorenz, 247 

 Olfactory organ, 214 

 Oligocene, 330, 335 

 Oligochaeta, 270 

 Onychophora, 274 

 Oocyte, 194, 196, 197 

 Oogenesis, 193, 194, 196-198 

 Oogonium, 59, 193, 194 

 Open ocean, 302, 303 

 Operculum, 116 



of tadpole, 214 

 Ophiurodica, 268 

 Ophthalmozoa, 247 

 ()pistho('0(>l()us vertebrae, 92 

 Optic nerve, 211, 213 



Paedogenesis, 166 

 Paleomastodon, 336, 339 

 Paleontology, 14, 21, 325-348 



and interrelated evolutions, 328, 329 

 Paleozoic, 330, 335 



Pallas's sand grouse, migration of, 319 

 Palolo, 270 

 Pancreas, 103, 105, 153, 155 



in embryo, 211, 212 

 Pancreatic juice, 105 

 Pandorina, reproduction of, 162 



spheroid colony in, 68 

 J^aramecium, 260, 261 



conjugating strains of, 164 



fission in, 169 



food vacuole in, 101 



reproduction of, 162, 163, 164, 1()8 



size of, 24 

 I'arasitisni, 287, 290, 291 

 Parathyroids, 163, 154 



