592 GLOSSARY. 



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



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



the Tteniada (Tapeworms 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. 

 OSTKACODA (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 gonophores or generative buds of the 



Hydrozoa. 



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

 OVIPAROUS (Lat. ovum, an egg; and par io, 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. 

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



their eggs after they are extruded from the body. 

 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 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 ; 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. 



PALLIUM (Lat. pallium, a cloak). The mantle of the Molly sea. Pallial : re- 

 lating 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. bragchia, gill). An old name for 

 the Bracldopoda, 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, de- 

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

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



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



PARAPODIA (Gr. para, beside ; poda, feet). The unarticulated lateral locomo- 

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



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

 the body. 



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

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

 and the viscera. 



PARTHENOGENESIS (Gr. partlienos, 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. 



PATAGIUM (Lat. the border of a dress). Applied to the expansion of the in- 

 tegument by which Bats, Flying Squirrels, and other animals support them- 

 selves in the air. 



PATELLA. The knee-cap or knee-pan. A sesamoid bone developed in the 

 tendon of insertion of the great extensor muscles of the thigh. 



