=Œ-soph´a-gus= [Gr. _oiso_, will bear; _phagein_, eat.] The gullet; the membranous tube through which food passes from the pharynx to the stomach. =On-tog´e-ny= [Gr. _on_, being; _genesis_, origin.] The history of the evolution of the individual; the development of the individual. =On-to-ge-net´ic= [Gr. _on_, being; _genesis_, origin.] Pertaining to ontogeny. =On-y-choph´o-ra= [Gr. _onyx_, claw; _pherein_, bear.] Arthropods including only a single genus, the curious caterpillar-like Peripatus. =Oösperm= [Gr. _oon_, egg; _sperma_, semen.] A fertilized ovum. The first stage in the existence of a human being is called oösperm. =O-per´cu-lum= [Lat. lid.] The gill-cover. =O-phid´i-a= [Gr. _ophis_, serpent.] Serpents; snakes. =Op-po´nens Hal-lu´cis= [Lat. _ob_, _pono_, to place over against; _hallux_, great toe.] The name of a muscle in the foot. =Or-do-vi´cian= [_ordovices_, ancient Celtic tribe in Wales.] =Or-nith-o-del´phi-a= [Gr. _ornis_, bird; _delphys_, womb.] A sub-class of oviparous mammals. =Or-o-hip´pus= [Gr. _oros_, mountain; _hippos_, horse.] =Or-tho-cer´a-tites= [Gr. _orthos_, straight; _keras_, horn.] =Os´te-o-blasts= [Gr. _osteon_, bone; _blastano_, sprout.] =Os´te-o-clasts= [Gr. _osteon_, bone; _klao_, destroy.] =Os´tra-co-derms= [Gr. _ostrakon_, shell; _derma_, skin.] =Ovum= [Lat. _egg_.] Female germ-cell; female, encysted, sexual cell. =O-vip´a-rous= [Lat. _ovum_, egg; _pairo_, produce.] Producing eggs that mature and are hatched outside the body. =Pal´li-um= [Gr. _mantle_.] =Pa-læ-o-lith´ic= [Gr. _palaios_, ancient; _lithos_, stone.] =Pa-læ-o-zo´ic= [Gr. _palaios_, ancient; _zoe_, life.] =Pan-do-ri´na mor´um= [Gr. Pandora; _moron_, mulberry.] =Pan-gen´e-sis= [Gr. _pas_, all; _genesis_, origin.] =Par-a-me´ci-um= [Gr. _paramekes_, of longish shape.] =Par-then-o-gen´e-sis= [Gr. _parthenos_, virgin; _genesis_, origin.] Production of a new individual from a virgin female without intervention of a male; reproduction by means of unfertilized eggs. =Per-en-ni-bran-chi-a´ta= [Lat. _perennis_, perpetual; _branchia_, gills.] =Per-en-ni-bran´chi-ates= [Vid. Perennibranchiata.] =Ped´al= [Lat. _pes_, foot.] =Per´mi-an= [Perm, Russia.] =Phan´er-o-gams= [Gr. _phaneros_, visible; _gamos_, marriage.] Flowering plants. =Phos-phor-es´cence.= =Phryn-o-ceph´a-lus mys-ta´ce-us.= =Phy-log´e-ny= [Gr. _phylon_, tribe; _genesis_, origin.] The history of the evolution of a species or group; distinguished from ontogeny. =Phy-lo-ge-net´ic= [Vid. phylogeny.] Pertaining to phylogeny. =Pith´e-coid= [Gr. _pithekos_, ape; _eidos_, like.] =Pith-e-can-thro´pus= [Gr. _pithekos_, ape; _anthropos_, man.] =Pla-gi-os´to-mi= [Gr. _plagios_, oblique; _stoma_, mouth.] A division of Elasmobranchii, including sharks and rays. =Pla-cen´tal= [Lat. _placenta_, cake.] So called on account of its shape. Pertaining to the _placenta_, the organ of attachment of higher vertebrate (monodelph) embryos to the wall of the uterus of the female.