INDEX 



Nostrils, 48; of Agnatha, 555 



Notochord, 153, 538, 542; of Branchwstoma, 



552; of vertebrates, 553 

 Nuclear envelope, see Nuclear membrane 

 Nuclear membrane, 21, 41 

 Nucleic acid, 22, 27, 618 

 Nucleolus, 21, 41 

 Nucleoproteins, 27, 28 

 Nucleotide, 27 

 Nucleus, 12, 38, 39, 146; differentiation of, 



165; o[ Amoeba, 228 

 Nudibranchia, 385 

 Numbers of species, arthropods, 424 

 Nutrition, of Mesozoa, 512; of Porifera, 512 

 .\yciotherus, 257 

 Nvmph, of locust. 453, 454; of paurometab- 



olous insects, 455; of squash bug, 463 

 .\ymf)hon, 480 



Oahu, land snails of, 652 



Ohelia, 301-302, 528 



Oceanic islands, 632; isolation of, 608 



Ocelli, 451 



Octopus, 270, 392 



Oculomotor nerve, 101 



Odonata, 459, 460, 485 



Odontognathae, 577 



Olfactory epithelium, 91, 109 



Olfactory nerve, 91 



Olfactory organ, 103 



Oligochaeta, 216, 396, 402-417; asexual re- 

 production in, 415; reproductive systems 

 of, 533 



Oligotrichida, 258 



Olvnthus, 274, 275 



Ommatidia, of crayfish eye, 435, 436, 437; 

 of insect eye, 452 



Omiis, 464 



Onagers, 625 



Ontogeny, 633 



Onychophora, 216, 219, 221, 449, 483-484; 

 water relations of, 602 



Oogenesis, 135, 138 139; in Hydra, 298 



Oogonium, 138 



Ofmlma, 257 



Open circulatory system, 515 



Operculum, of gastropods, 383 



Ophidia, 567, 573 



Ophiopholis, 498 



Ophiopluteus larva, 498, 499, 501 



Ophiuroidea, 216, 486, 497-499 



Opisthosoma, of chelicerates, 480 



Opossum, 162, 579, 582, 583, 585, 608 



Optic chiasma, 103 



Optic cups, 154, 167 



Optic lobes, 102 



Optic nerve, 91, 103 



Optic tracts, 103 



Optic vesicles, 154 



Oral disk, 307 



Oral groove, 249 



Oral pharynx, 48 



Orangutan, 587, 638 



Orconectes, 425 



Ordovician Period, and early fishes, 555; and 



origin of chordates, 540 

 Oreasler, 497 

 Organ culture, 17 

 Organic compounds, 22 



Organic evolution, 616, 619; Theory of, 655 

 Organismal Theory, 12 

 Organ of Corti, 108, 110 

 Organs, 10, 47, 58, 69; of Hydra, 292; of 



invertebrates, 510; of special sense, 87, 91 

 Organ systems, of invertebrates, 510 

 Organ systems, vertebrate, related to coor- 

 dination, 87-91; related to metabolism, 



47-58; related to reproduction, 128-132 

 Origin of Species, 218, 648 

 OrmthorhytKhm, 131, 579, 581, 630 

 Ornithosuchus. 575 

 Orthoncctida. 270, 271 

 Orthoptera, 443, 457, 461, 462 

 Osculum, 274 

 Osmosis, 601 

 Osphradium, 374 

 Osseous tissue, see Bone 

 Osteichthyes, 216, 541, 555, 557-560 

 Ostia, of gills, pelecypods, 372; of heart, 



arthropods, 515; of heart, cravfish; 432; 



of heart, locust, 450; of heart, pelecvpods, 



515 

 Ostium, 130; of sponge, 278 

 Ostracoda, 437 

 Ostracodermi, 541, 555 

 Ostrich, 574, 577, 578 

 Otolith membrane, 109 

 Otter, 587 



Ovary, 122, 130; o{ Hydra, 298 

 Oviducts, 130; of mammals, 134 

 Oviparity, 131 

 Oviparous reproduction, in lizards and snakes, 



571; in prototherians, 579; in reptiles, 565 

 Oviposition, of locust, 453 

 Ovisac, 131 

 Ovoviviparity, 131 

 Ovoviviparous reproduction, in Diptera, 534; 



in JVatrix, 571; in reptiles, 566 

 Ovulation, 131 

 Ovum, 134, 139, 143, 192 

 Oxidative metabolism, 20 

 Oxygen, 37, 54, 79, 81, 114; as environmental 



factor, 599-601 

 Oxyhemoglobin, 81 

 Oxytocic principle, 118 

 Oyster, 376, 379, 380 



/\ generation, 175 

 Paddlefish, 558 

 Pain, 91, 103 



698 



