PACHYDERMS. — A group of Mammalia, so called from their thick skins, and including the elephant, rhinoceros, hippopotamus, etc.

PALAEOZOIC. — The oldest system of fossiliferous rocks.

PALPI. — Jointed appendages to some of the organs of the mouth in insects and Crustacea.

PAPILIONACEAE. — An order of plants (see LEGUMINOSAE), The flowers of these plants are called PAPILIONACEOUS, or butterfly-like, from the fancied resemblance of the expanded superior petals to the wings of a butterfly.

PARASITE. — An animal or plant living upon or in, and at the expense of, another organism.

PARTHENOGENESIS. — The production of living organisms from unimpregnated eggs or seeds.