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PLANTIGRADES Quadrupeds which walk upon the whole sole of the foot, like the Bears.

PLASTIC Readily capable of change.

PLEISTOCENE PERIOD The latest portion of the Tertiary epoch.

PLUMULE (in plants) The minute bud between the seed-leaves of newly-germinated plants.

PLUTONIC ROCKS Rocks supposed to have been produced by igneous action in the depths of the earth.

POLLEN The male element in flowering plants; usually a fine dust produced by the anthers, which, by contact with the stigma effects the fecundation of the seeds. This impregnation is brought about by means of tubes (pollen-tubes) which issue from the pollen-grains adhering to the stigma, and penetrate through the tissues until they reach the ovary.

POLYANDROUS (flowers) Flowers having many stamens.

POLYGAMOUS PLANTS Plants in which some flowers are unisexual and others hermaphrodite. The unisexual (male and female) flowers, may be on the same or on different plants.

POLYMORPHIC Presenting many forms.

POLYZOARY The common structure for the Polyzoa, such as the well-known Sea-mats.

PREHENSILE Capable of grasping.

PREPOTENT Having a superiority of power.

PRIMARIES The feathers forming the tip of the wing of a bird, and inserted upon that part which represents the hand of man.

PROCESSES Projecting portions of bones, usually for the attachment of muscles, ligaments, &c.

PROPOLIS A resinous material collected by the Hive-Bees from the opening buds of various trees.

PROTEAN Exceedingly variable.

PROTOZOA The lowest great division of the Animal Kingdom. These animals are composed of a gelatinous material, and show scarcely any trace of distinct organs. The Infusoria, Foraminifera, and Sponges, with some other forms, belong to this division.

PUPA (pl PUPÆ). The second stage in the development of an Insect, from which it emerges in the perfect (winged) reproductive form. In most insects the pupal stage is passed in perfect repose. The chrysalis is the pupal state of butterflies.

RADICLE The minute root of an embryo plant.

RAMUS One half of the lower jaw in the Mammalia. The portion which rises to articulate with the skull is called the ascending ramus.

RANGE The extent of country over which a plant or animal is naturally spread. Range in time expresses the distribution of a species or group through the fossiliferous beds of the earth’s crust.

RETINA The delicate inner coat of the eye, formed by nervous filaments spreading from the optic nerve, and serving for the perception of the impressions produced by light.

RETROGRESSION Backward development. When an animal, as it approaches maturity, becomes less perfectly organised than might be expected from its early stages and known relationships, it is said to undergo a retrograde development or metamorphosis.

RHIZOPODS A class of lowly organised animals (protozoa), having a gelatinous body, the surface of which can be protruded in the form of root-like processes or filaments, which serve for locomotion and the prehension of food. The most important order is that of the Foraminifera.

RODENTS The gnawing Mammalia, such as the Rats, Rabbits, and Squirrels. They are especially characterised by the possession of a single pair of chisel-like cutting teeth in each jaw, between which and the grinding teeth there is a great gap.

RUBUS The Bramble Genus.

RUDIMENTARY Very imperfectly developed.

RUMINANTS The group of Quadrupeds which ruminate or chew the cud, such as oxen, sheep, and deer. They have divided hoofs, and are destitute of front teeth in the upper jaw.

SACRAL Belonging to the sacrum, or the bone composed usually of two or more united vertebrae to which the sides of the pelvis in Vertebrate animals are attached.

SARCODE The gelatinous material of which the bodies of the lowest animals (Protozoa) are composed.

SCUTELLÆ The horny plates with which the feet of birds are generally more or less covered, especially in front.

SEDIMENTARY Formations Rocks deposited as sediments from water.

SEGMENTS The transverse rings of which the body of an articulate animal or Annelid is composed.

SEPALS The