=Oxygen.= A gas which is one of the constituent parts of water and of atmospheric air. It is essential to animal life. =Oviparous= (L. _ovum_, an egg; _pario_, I bring forth). The animals which bring forth eggs. =Operculum= (from the Latin for lid). Applied to the horny or shelly plate which closes certain univalve shells, as the Whelk, Periwinkle, &c. =Papillæ= (L. _papilla_, a nipple). Soft prominences which resemble in form the teats of animals. =Palpi= (L. _palpo_, I touch). The organs of touch commonly called 'feelers,' developed from the lablum and maxillæ of insects. =Pectinated= (L. _pecten_, a comb). Toothed like a comb. =Physograde= (Gr. _physis_, air; _gradior_, I advance). The acalephes that swim by means of air-bladders. =Phytophagous= (Gr. _phuton_, a plant; _phago_, I eat). Plant-eating animals. =Pulmonigrade= (L. _pulmo_, a lung; _gradior_, I walk). The tribe of Medusæ which swim by contraction of the respiratory disc. =Rotifera= (L. _rota_, a wheel; _fero_, I bear). The name of a class of infusorial animalcules, characterized by the vibratile and apparently rotating ciliary organs upon the heads. =Rhodospermes.= The red-coloured sea-weeds. =Serrated= (L. _serra_, a saw). Toothed like a saw. =Sessile.= Attached by a base. =Silicious= (L. _silex_, a flint). Flinty. =Setæ.= Bristles, or similar parts. =Spicula= (L. _spiculum_, a point or dart). Fine-pointed bodies, like needles. =Tuberculate.= Warty, or carved with small rounded knobs. =Testacea= (L. _testa_, a shell). Molluscs with a shelly covering, as the Oyster, Whelk, &c. =Univalve= (L. _unus_, one; _valvæ_, doors). A shell composed of one calcareous piece, as the Periwinkle. =Umbones.= The base of a shell about the hinge. =Viviparous= (L. _vivus_, alive; _pario_, I bring forth). The animals which bring forth their young alive. See Oviparous. =Whorl.= The spiral turn of a shell. =Zoology= (Gr. _zoon_, animal; _logos_, a discourse). That branch of science that treats of the habits, structure, and classification of animals. =Zoologist.= One who is acquainted with the science of Zoology. =Zoophyte= (Gr. _zoon_, an animal; _phyton_, a plant). The lowest primary division of the animal kingdom, which includes many animals that are fixed to the ground and have the form of plants. INDEX. _Animalculæ_, 37. _Actiniæ_ (Sea anemones), 38, 47. _mesembryanthemum_, 48, 365. _troglodytes_, 51, 62. _bellis_, 56. _dianthus_, 57, 62, 154, 366. _crassicornis_, 61, 100. _coriacea_, 56. _parasitica_, 66. _explorator_, 51. Acorn barnacles, 145. Adductor muscle, 178, 182. Annelids, 154, 191, 315. _Acalephæ_, 203. Alternation of generations, 214. _Aphrodite aculeata_, 267. _Aplysiæ_, 54, 309, 311. _Aquariæ_ (on the formation of marine), 357. _Anomoura_ (Hermit crabs), 69, 92, 130, 133. _Asteriadæ_, 271. Algæ, 97. _A. ventilabrum_, 161. Amphitrite, 162. _Buccinum undutum_, 92.