Ovisac

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, etc.

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. bragchia, 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 which 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, developed from certain of the oral appendages in Insects, Spiders, and Crustacea, and from the sides of the mouth 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. para, beside; podes, feet). The unarticulated lateral locomotive 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. splagchna, viscera). Applied to one of the nervous ganglia of the Mollusca, which supplies the walls of the body and the viscera.

Parthenogenesis

(Lat. 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.

Patagium

(Lat. the border of a dress). Applied to the expansion of the integument by which Bats, Flying Squirrels, and other animals support themselves 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.

Pauropoda

(Gr. pauros, little ; podes, feet). An order of Myriapoda.