Charles Darwin: The Origin of Species by means of Natural Selection

GLOSSARY 1. GLOSSARY OF THE PRINCIPAL SCIENTIFIC TERMS USED IN THE PRESENT VOLUME. (continued)

OPERCULUM.--A calcareous plate employed by many Molluscae to close the aperture of their shell. The OPERCULAR VALVES of Cirripedes are those which close the aperture of the shell.

ORBIT.--The bony cavity for the reception of the eye.

ORGANISM.--An organised being, whether plant or animal.

ORTHOSPERMOUS.--A term applied to those fruits of the Umbelliferae which have the seed straight.

OSCULANT.--Forms or groups apparently intermediate between and connecting other groups are said to be osculant.

OVA.--Eggs.

OVARIUM or OVARY (in plants).--The lower part of the pistil or female organ of the flower, containing the ovules or incipient seeds; by growth after the other organs of the flower have fallen, it usually becomes converted into the fruit.

OVIGEROUS.--Egg-bearing.

OVULES (of plants).--The seeds in the earliest condition.

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.

PEDUNCULATED.--Supported upon a stem or stalk. The pedunculated oak has its acorns borne upon a footstool.

PELORIA or PELORISM.--The appearance of regularity of structure in the flowers of plants which normally bear irregular flowers.