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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, &c, 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. (esophagus.—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 Mollusca 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 Dmbelliferte 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, &c.

Paljeozoic—The oldest system of fossiliferous rocks.

Palpi.—Jointed appendages to some of the organs of the mouth in Insects and Crustacea

Papilionace^:.—An order of Plants (see Leguminos.s:).—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 unhnpreg

nated eggs or seeds. Pedunculated.—Supported upon a stem or stalk. The pedunculated oak

has its acorns borne upon a footstalk. Peloria or Pelorism.—The appearance of regularity of structure in the

flowers of plants which normally bear irregular Bowers. 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.

They are usually of delicate texture and brightly coloured. Phyllodineous.—Having flattened, leaf-like twigs or leafstalks instead of

true leaves.

Pigment.—The colouring material produced generally in the superficial

parts of animals. The cells secreting it are called pigment-cells. Pinnate.—Bearing leaflets on each side of a central stalk. Pistils.—The female organs of a flower, which occupy a position in the

centre of the other floral organs. The pistil is generally divisible into

the ovary or germen, the style and the stigma. Placentalia, Placentata, or Placental Mammals.—See Mammalia. 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 newlygerminated 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 formed by the cells of the Pplyzot,

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. Pup^e).—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 apr proaches maturity, becomes less perfectly organised than might b.i 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 rootlike 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 Genas.

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 vertebra? 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. Scutell^:.—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. Seoments.—The transverse rings of which the body of an articulate

animal or Annelid is composed. Sepals.—The leaves or segments of the calyx, or outermost envelope of

an ordinary flower. They are usually green, but sometimes brightly

coloured.

Serratures.—Teeth like those of a saw.
Sessile.—Not supported on a stem or footstalk.

Silurian System.—A very ancient system of fossiliferous rocks belonging to the earlier part of the Paleozoic series.

Specialisation.—The setting apart of a particular organ for the performance of a particular function.

Spinal Chord.—The central portion of the nervous system in the Vertebrata, which descends from the brain through the arches of the vertebrse, and gives off nearly all the nerves to the various organs of the body.

Stamens.—The male organs of flowering plants, standing in a circle within the petals. They usually consist of a filament and an anther, the anther being the essential part in which the pollen, or fecundating dust, is formed.

Sternum.—The breast-bone.

Stigma.—The apical portion of the pistil in flowering plants.

Stipules.—Small leafy organs placed at the base of the footstalks of the

leaves in many plants. Style.—The middle portion of the perfect pistil, which rises like a column

from the ovary and supports the stigma at its summit. Subcutaneous.—Situated beneath the skin. Suctorial.—Adapted for sucking.

Sutures (in the skull).—The lines of junction of the bones of which the skull is composed.

Tarsus (pi. Tarsi).—The jointed feet of articulate animals, such as Insects.

Teleostean Fishes.—Fishes of the kind familiar to us in the present day, having the skeleton usually completely ossified and the scales horny.

Tentacula or Tentacles —Delicate fleshy organs of prehension or touch possessed by many of the lower animals.

Tertiary.—The latest geological epoch, immediately preceding the establishment of the present order of things.

Trachea.—The wind-pipe or passage for the admission of air to the lungs.

Tridactyle.—Three-fingered, or composed of three movable parts attached to a common base.

Tbilobites.—A peculiar groupof extinct Crustaceans, somewhat resembling the Woodlice in external form, and, like some of them, capable of rolling themselves up into a ball. Their remains are found only in the Palseozoic rocks, and most abundantly in those of Silurian age.

Trimorphic—Presenting three distinct forms.

Umbellifer.e.—An order of plants in which the flowers, which contain five stamens and a pistil with two styles, are supported upon footstalks which spring from the top of the flower stem and spread out like the wires of an umbrella, so as to bring all the flowers in the same head (umbel) nearly to the same level. (Examples, Parsley and Carrot.)

Ungulata.—Hoofed quadrupeds.
Unicellular.—Consisting of a single cell.

Vascular.—Containing blood-vessels.
Vermiform.—Like a worm.

Vertebrata: or Vertebrate Animals.—The highest division of the animal kingdom, so called from the presence in most cases of a backbone composed of numerous joints or vertebrae, which constitutes the centre of the skeleton and at the same time supports and protects the central parts of the nervous system.

WfiORLS.—The circles or spiral lines in which the parts of plants are

arranged upon the axis of growth. Workers.—See Neuters.

Zoea-stage.—The earliest stage in the development of many of the higher Crustacea, so called from the name of Zoea applied to these young animals when they were supposed to constitute a peculiar genus.

Zooms. —In many of the lower animals (such as the Corals, Medusse, &c.) reproduction takes place in two ways, namely, by means of eggs and by a process of budding with or without separation from the parent of the product of the latter, which is often very different from that of the egg. The individuality of the species is represented by the whole of the form produced between two sexual reproductions; and these forms, which are apparently individual animals, have been called zooids.

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