8o8 GLOSSARY. 



ORAL (Lat. os, mouth). Connected with the mouth. 



ORNITHODELPHIA (Gr. ornis, a bird ; delphus, Avomb). The primary division 



of Mammals comprising the Monotremata. 

 ORNITHOSCELIDA (Gr. ornis, bird ; skelos, leg). Applied by Huxley to the 



Deinosaurian Eeptiles, together with the genus Compsognathus, on account 



of the bird-like characters of their hind-limbs. 

 ORTHOCERATIDJS (Gr. orthos, straight ; keras, horn). A family of the Nau- 



tilidce, in which the shell is straight, or nearly so. 

 ORTHOPTERA (Gr. orthos, straight ; pteron, Aving). An order of Insects. 

 OSCULA (Lat. diminutive of os, mouth). 1. The large apertures by Avhich a 



sponge is perforated ("exhalant apertures"). 2. The suckers with which 



the Tceniada (Tape-worms and Cystic Worms) are provided. 

 OSSICULA (Lat. diminutive of os, bone). Literally small bones. Often used 



to designate any hard structures of small size, such as the calcareous plates 



in the integument of the Star-fishes. 

 OSTRACODA (Gr. ostrakon, a shell). An order of small Crustaceans which are 



enclosed in bivalve shells. 

 OTOLITHS (Gr. ous, ear ; and lithos, stone). The calcareous bodies connected 



with the sense of hearing, even in its most rudimentary form. 

 OVARIAN VESICLES or CAPSULES. The generative buds of the Sertularida. 

 OVARY (OVARIUM). The organ by which ova are produced. 

 OVIPAROUS (Lat. ovum, an egg ; andpario, I bring forth). Applied to animals 



which bring forth eggs, in contradistinction to those which bring forth their 



young alive. 



OVIPOSITOR (Lat. ovum; and pono, I place). The organ possessed by some in- 

 sects, by means of which the eggs are placed in a position suitable for their 



development. 

 OVISAC. The external bag or sac in which certain of the Invertebrates carry 



their eggs after they are extruded from the body. 

 OVOVTVIPAROUS (Lat. ovum, egg ; vivus, alive ; pario, I produce). Applied to 



animals which retain their eggs within the body until they are hatched. 

 OVUM (Lat. an egg). The germ produced within the ovary, and capable under 



certain conditions of being developed into a new individual. 



PACHYDERMATA (Gr. pachus, thick ; derma, skin). An old Mammalian order 

 constituted by Cuvier for the reception of the .Rhinoceros, Hippopotamus, 

 Elephant, &c. 



PALAEONTOLOGY (Gr. palaios, ancient ; onta, beings ; and logos, discourse). The 

 science of fossil remains or of extinct organised beings. 



PALAEOZOIC (Gr. palaios, ancient ; and zoe, life). Applied to the oldest of the 

 great geological epochs. 



PALLIOBRANCHIATA (Lat. pallium, a cloak ; and Gr. Iraychia, gill). An old 

 name for the Brachiopoda, founded upon the belief that the system of tubes 

 in the mantle constituted the gills. 



PALLIUM (Lat. a cloak). The mantle of the Mollusca. Pallial; relating to 

 the mantle. Pallial line or impression; the line left in the dead shell 

 by the muscular margin of the mantle. Pallial shell ; a shell Avhich is 

 secreted by, or contained within, the mantle, such as the "bone" of the 

 Cuttle-fishes. 



PALPI (Lat. palpo, I touch). Processes supposed to be organs of touch, de- 

 veloped from certain of the oral appendages in Insects, Spiders, and Crus- 

 tacea, and from the sides of the moiith in the Acephalous Molluscs. 



PANSPERMY (Gr. pan, all ; sperma, seed). The theory that living beings are 

 never produced except from pre-existent living beings. 



PAPILLA (Lat. for nipple). A minute soft prominence. 



PARAPODIA (Gr.^ara, beside ',podes, feet). The unarticulated lateral locomo- 

 tive processes or " foot-tubercles " of many of the Annelida. 



PARIETAL (Lat. paries, a wall). Connected with the Avails of a cavity or of the 

 body. 



PARIETOSPLANCHNIC (Lat. paries; Gr. splagchna, viscera). Applied to one 

 of the nervous ganglia of the Mollusca, Avhich supplies the Avails of the body 

 and the viscera. 



