(Examples, grasses, lilies, orchids, palms, etc.) MORAINES .-- The accumulations of fragments of rock brought down by glaciers.
MORPHOLOGY .-- The law of form or structure independent of function.
MYSIS-STAGE .-- A stage in the development of certain crustaceans (prawns), in which they closely resemble the adults of a genus (Mysis) belonging to a slightly lower group.
NASCENT .-- Commencing development.
NATATORY .-- Adapted for the purpose of swimming.
NAUPLIUS-FORM .-- The earliest stage in the development of many Crustacea, especially belonging to the lower groups.

In this stage the animal has a short body, with indistinct indications of a division into segments, and three pairs of fringed limbs.

This form of the common fresh-water CYCLOPS was described as a distinct genus under the name of NAUPLIUS.
NEURATION .-- The arrangement of the veins or nervures in the wings of insects.
NEUTERS .-- Imperfectly developed females of certain social insects (such as ants and bees), which perform all the labours of the community.
Hence, they are also called WORKERS.
NICTITATING MEMBRANE .-- A semi-transparent membrane, which can be drawn across the eye in birds and reptiles, either to moderate the effects of a strong light or to sweep particles of dust, etc., from the surface of the eye.
OCELLI .-- The simple eyes or stemmata of insects, usually situated on the crown of the head between the great compound eyes.
OESOPHAGUS .-- The gullet.
OOLITIC .-- A great series of secondary rocks, so called from the texture of some of its members, which appear to be made up of a mass of small EGG-LIKE calcareous bodies.
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.
PELVIS .-- The bony arch to which the hind limbs of vertebrate animals are articulated.
PETALS .-- The leaves of the corolla, or second circle of organs in a flower.