804 MANUAL OP ZOOLOGY. 



ORTHOPTERA (Or. orthos, straight ; pteron, wing). An order of Insects. 



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

 sponge is perforated (' exhalent 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 con- 

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



OVARIAN VESICLES or CAPSULES. The gonophores or generative buds of 

 the Hydruzoa. 



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



OVIPAROUS (Lat. ovum, an egg ; and pario, I bring forth). Applied to ani- 

 mals 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 

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

 their development. 



OVOVIVIPAROUS (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 OA T ary, and capable 

 under certain conditions of being developed into a new individual. 



PALEONTOLOGY (Gr. palaios, ancient ; and logos, discourse. The science of 

 fossil remains or of extinct, organised beings. 



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

 the great geological epochs. 



PALLIUM (Lat. pallium, 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 

 which is secreted by, or contained within, the mantle, such as the ' bone ' 

 of the Cuttle-fishes. 



PALLIOBRANCHIATA (Lat. pallium ; and Gr. hragchia, gill). An old name for 

 the Brachiopoda, founded upon the belief that the system of tubes in 

 the mantle constituted the gills. 



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

 developed from certain of the oral appendages in Insects, Spiders, and 

 Crustacea ; and from the sides of the mouth in the Acephalous Molluscs. 



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



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

 the body. 



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

 of the nervous ganglia of the Mollusca, which supplies the walls of the 

 body and the viscera. 



PARTHENOGENESIS (Gr. parthenos, a virgin; and gignomai, to be born). 

 Strictly speaking, confined to the production of new individuals from 

 virgin females by means of ova, without the intervention of a male. 

 Sometimes used also to designate asexual reproduction by gemmation or 

 fission. 



PECTINATE (Lat. pecten, a comb). Comb-like ; applied to the gills of cer- 

 tain Gasteropods, hence called Pectinibranchiata. 



PEDAL (Lat. pes, the foot). Connected with the foot of Mollusca. 



PEDICELLARI.E (Lat. p'.dicellus, a louse). Certain singular appendages found 



