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(I am indebted to the kindness of Mr. W.S. Dallas for this Glossary, whichhas been given because several readers have complained to me that some ofthe terms used were unintelligible to them. Mr. Dallas has endeavoured togive the explanations of the terms in as popular a form as possible.)

ABERRANT.--Forms or groups of animals or plants which deviate in importantcharacters from their nearest allies, so as not to be easily included inthe same group with them, are said to be aberrant.

ABERRATION (in Optics).--In the refraction of light by a convex lens therays passing through different parts of the lens are brought to a focus atslightly different distances--this is called SPHERICAL ABERRATION; at thesame time the coloured rays are separated by the prismatic action of thelens and likewise brought to a focus at different distances--this isCHROMATIC ABERRATION.

ABNORMAL.--Contrary to the general rule.

ABORTED.--An organ is said to be aborted, when its development has beenarrested at a very early stage.

ALBINISM.--Albinos are animals in which the usual colouring matterscharacteristic of the species have not been produced in the skin and itsappendages. Albinism is the state of being an albino.

ALGAE.--A class of plants including the ordinary sea-weeds and thefilamentous fresh-water weeds.

ALTERNATION OF GENERATIONS.--This term is applied to a peculiar mode ofreproduction which prevails among many of the lower animals, in which theegg produces a living form quite different from its parent, but from whichthe parent-form is reproduced by a process of budding, or by the divisionof the substance of the first product of the egg.

AMMONITES.--A group of fossil, spiral, chambered shells, allied to theexisting pearly Nautilus, but having the partitions between the chamberswaved in complicated patterns at their junction with the outer wall of theshell.

ANALOGY.--That resemblance of structures which depends upon similarity offunction, as in the wings of insects and birds. Such structures are saidto be ANALOGOUS, and to be ANALOGUES of each other.

ANIMALCULE.--A minute animal: generally applied to those visible only bythe microscope.

ANNELIDS.--A class of worms in which the surface of the body exhibits amore or less distinct division into rings or segments, generally providedwith appendages for locomotion and with gills. It includes the ordinarymarine worms, the earth-worms, and the leeches.

ANTENNAE.--Jointed organs appended to the head in Insects, Crustacea andCentipedes, and not belonging to the mouth.

ANTHERS.--The summits of the stamens of flowers, in which the pollen orfertilising dust is produced.

APLACENTALIA, APLACENTATA or APLACENTAL MAMMALS.--See MAMMALIA.

ARCHETYPAL.--Of or belonging to the Archetype, or ideal primitive form uponwhich all the beings of a group seem to be organised.

ARTICULATA.--A great division of the Animal Kingdom characterised generallyby having the surface of the body divided into rings called segments, agreater or less number of which are furnished with jointed legs (such asInsects, Crustaceans and Centipedes).

ASYMMETRICAL.--Having the two sides unlike.

ATROPHIED.--Arrested in development at a very early stage.

BALANUS.--The genus including the common Acorn-shells which live inabundance on the rocks of the sea-coast.

BATRACHIANS.--A class of animals allied to the Reptiles, but undergoing apeculiar metamorphosis, in which the young animal is generally aquatic andbreathes by gills. (Examples, Frogs, Toads, and Newts.)

BOULDERS.--Large transported blocks of stone generally embedded in clays orgravels.

BRACHIOPODA.--A class of marine Mollusca, or soft-bodied animals, furnishedwith a bivalve shell, attached to submarine objects by a stalk which passesthrough an aperture in one of the valves, and furnished with fringed arms,by the action of which food is carried to the mouth.

BRANCHIAE.--Gills or organs for respiration in water.

BRANCHIAL.--Pertaining to gills or branchiae.

CAMBRIAN SYSTEM.--A series of very ancient Palaeozoic rocks, between theLaurentian and the Silurian. Until recently these were regarded as theoldest fossiliferous rocks.

CANIDAE.--The Dog-family, including the Dog, Wolf, Fox, Jackal, etc.

CARAPACE.--The shell enveloping the anterior part of the body inCrustaceans generally; applied also to the hard shelly pieces of theCirripedes.

CARBONIFEROUS.--This term is applied to the great formation which includes,among other rocks, the coal-measures. It belongs to the oldest, orPalaeozoic, system of formations.

CAUDAL.--Of or belonging to the tail.

CEPHALOPODS.--The highest class of the Mollusca, or soft-bodied animals,characterised by having the mouth surrounded by a greater or less number offleshy arms or tentacles, which, in most living species, are furnished withsucking-cups. (Examples, Cuttle-fish, Nautilus.)

CETACEA.--An order of Mammalia, including the Whales, Dolphins, etc.,having the form of the body fish-like, the skin naked, and only the forelimbs developed.

CHELONIA.--An order of Reptiles including the Turtles, Tortoises, etc.

CIRRIPEDES.--An order of Crustaceans including the Barnacles and Acorn-shells. Their young resemble those of many other Crustaceans in form; butwhen mature they are always attached to other objects, either directly orby means of a stalk, and their bodies are enclosed by a calcareous shellcomposed of several pieces, two of which can open to give issue to a bunchof curled, jointed tentacles, which represent the limbs.

COCCUS.--The genus of Insects including the Cochineal. In these the maleis a minute, winged fly, and the female generally a motionless, berry-likemass.

COCOON.--A case usually of silky material, in which insects are frequentlyenveloped during the second or resting-stage (pupa) of their existence. The term "cocoon-stage" is here used as equivalent to "pupa-stage."

COELOSPERMOUS.--A term applied to those fruits of the Umbelliferae whichhave the seed hollowed on the inner face.

COLEOPTERA.--Beetles, an order of Insects, having a biting mouth and thefirst pair of wings more or less horny, forming sheaths for the secondpair, and usually meeting in a straight line down the middle of the back.

COLUMN.--A peculiar organ in the flowers of Orchids, in which the stamens,style and stigma (or the reproductive parts) are united.

COMPOSITAE or COMPOSITOUS PLANTS.--Plants in which the inflorescenceconsists of numerous small flowers (florets) brought together into a densehead, the base of which is enclosed by a common envelope. (Examples, theDaisy, Dandelion, etc.)

CONFERVAE.--The filamentous weeds of fresh water.

CONGLOMERATE.--A rock made up of fragments of rock or pebbles, cementedtogether by some other material.

COROLLA.--The second envelope of a flower usually composed of coloured,leaf-like organs (petals), which may be united by their edges either in thebasal part or throughout.

CORRELATION.--The normal coincidence of one phenomenon, character, etc.,with another.

CORYMB.--A bunch of flowers in which those springing from the lower part ofthe flower stalks are supported on long stalks so as to be nearly on alevel with the upper ones.

COTYLEDONS.--The first or seed-leaves of plants.

CRUSTACEANS.--A class of articulated animals, having the skin of the bodygenerally more or less hardened by the deposition of calcareous matter,breathing by means of gills. (Examples, Crab, Lobster, Shrimp, etc.)

CURCULIO.--The old generic term for the Beetles known as Weevils,characterised by their four-jointed feet, and by the head being producedinto a sort of beak, upon the sides of which the antennae are inserted.

CUTANEOUS.--Of or belonging to the skin.

DEGRADATION.--The wearing down of land by the action of the sea or ofmeteoric agencies.

DENUDATION.--The wearing away of the surface of the land by water.

DEVONIAN SYSTEM or FORMATION.--A series of Palaeozoic rocks, including theOld Red Sandstone.

DICOTYLEDONS, or DICOTYLEDONOUS PLANTS.--A class of plants characterised byhaving two seed-leaves, by the formation of new wood between the bark andthe old wood (exogenous growth) and by the reticulation of the veins of theleaves. The parts of the flowers are generally in multiples of five.

DIFFERENTATION.--The separation or discrimination of parts or organs whichin simpler forms of life are more or less united.

DIMORPHIC.--Having two distinct forms.--DIMORPHISM is the condition of theappearance of the same species under two dissimilar forms.

DIOECIOUS.--Having the organs of the sexes upon distinct individuals.

DIORITE.--A peculiar form of Greenstone.

DORSAL.--Of or belonging to the back.

EDENTATA.--A peculiar order of Quadrupeds, characterised by the absence ofat least the middle incisor (front) teeth in both jaws. (Examples, theSloths and Armadillos.)

ELYTRA.--The hardened fore-wings of Beetles, serving as sheaths for themembranous hind-wings, which constitute the true organs of flight.

EMBRYO.--The young animal undergoing development within the egg or womb.

EMBRYOLOGY.--The study of the development of the embryo.

ENDEMIC.--Peculiar to a given locality.

ENTOMOSTRACA.--A division of the class Crustacea, having all the segmentsof the body usually distinct, gills attached to the feet or organs of themouth, and the feet fringed with fine hairs. They are generally of smallsize.

EOCENE.--The earliest of the three divisions of the Tertiary epoch ofgeologists. Rocks of this age contain a small proportion of shellsidentical with species now living.

EPHEMEROUS INSECTS.--Insects allied to the May-fly.

FAUNA.--The totality of the animals naturally inhabiting a certain countryor region, or which have lived during a given geological period.

FELIDAE.--The Cat-family.

FERAL.--Having become wild from a state of cultivation or domestication.

FLORA.--The totality of the plants growing naturally in a country, orduring a given geological period.

FLORETS.--Flowers imperfectly developed in some respects, and collectedinto a dense spike or head, as in the Grasses, the Dandelion, etc.

FOETAL.--Of or belonging to the foetus, or embryo in course of development.

FORAMINIFERA.--A class of animals of very low organisation and generally ofsmall size, having a jelly-like body, from the surface of which delicatefilaments can be given off and retracted for the prehension of externalobjects, and having a calcareous or sandy shell, usually divided intochambers and perforated with small apertures.

FOSSILIFEROUS.--Containing fossils.

FOSSORIAL.--Having a faculty of digging. The Fossorial Hymenoptera are agroup of Wasp-like Insects, which burrow in sandy soil to make nests fortheir young.

FRENUM (pl. FRENA).--A small band or fold of skin.

FUNGI (sing. FUNGUS).--A class of cellular plants, of which Mushrooms,Toadstools, and Moulds, are familiar examples.

FURCULA.--The forked bone formed by the union of the collar-bones in manybirds, such as the common Fowl.

GALLINACEOUS BIRDS.--An order of birds of which the common Fowl, Turkey,and Pheasant, are well-known examples.

GALLUS.--The genus of birds which includes the common Fowl.

GANGLION.--A swelling or knot from which nerves are given off as from acentre.

GANOID FISHES.--Fishes covered with peculiar enamelled bony scales. Mostof them are extinct.

GERMINAL VESICLE.--A minute vesicle in the eggs of animals, from which thedevelopment of the embryo proceeds.

GLACIAL PERIOD.--A period of great cold and of enormous extension of iceupon the surface of the earth. It is believed that glacial periods haveoccurred repeatedly during the geological history of the earth, but theterm is generally applied to the close of the Tertiary epoch, when nearlythe whole of Europe was subjected to an arctic climate.

GLAND.--An organ which secretes or separates some peculiar product from theblood or sap of animals or plants.

GLOTTIS.--The opening of the windpipe into the oesophagus or gullet.

GNEISS.--A rock approaching granite in composition, but more or lesslaminated, and really produced by the alteration of a sedimentary depositafter its consolidation.

GRALLATORES.--The so-called wading-birds (storks, cranes, snipes, etc.),which are generally furnished with long legs, bare of feathers above theheel, and have no membranes between the toes.

GRANITE.--A rock consisting essentially of crystals of felspar and mica ina mass of quartz.

HABITAT.--The locality in which a plant or animal naturally lives.

HEMIPTERA.--An order or sub-order of insects, characterised by thepossession of a jointed beak or rostrum, and by having the fore-wings hornyin the basal portion and membranous at the extremity, where they cross eachother. This group includes the various species of bugs.

HERMAPHRODITE.--Possessing the organs of both sexes.

HOMOLOGY.--That relation between parts which results from their developmentfrom corresponding embryonic parts, either in different animals, as in thecase of the arm of man, the fore-leg of a quadruped, and the wing of abird; or in the same individual, as in the case of the fore and hind legsin quadrupeds, and the segments or rings and their appendages of which thebody of a worm, a centipede, etc., is composed. The latter is calledserial homology. The parts which stand in such a relation to each otherare said to be homologous, and one such part or organ is called thehomologue of the other. In different plants the parts of the flower arehomologous, and in general these parts are regarded as homologous withleaves.

HOMOPTERA.--An order or sub-order of insects having (like the Hemiptera) ajointed beak, but in which the fore-wings are either wholly membranous orwholly leathery, The Cicadae, frog-hoppers, and Aphides, are well-knownexamples.

HYBRID.--The offspring of the union of two distinct species.

HYMENOPTERA.--An order of insects possessing biting jaws and usually fourmembranous wings in which there are a few veins. Bees and wasps arefamiliar examples of this group.

HYPERTROPHIED.--Excessively developed.

ICHNEUMONIDAE.--A family of hymenopterous insects, the members of which laytheir eggs in the bodies or eggs of other insects.

IMAGO.--The perfect (generally winged) reproductive state of an insect.

INDIGENES.--The aboriginal animal or vegetable inhabitants of a country orregion.

INFLORESCENCE.--The mode of arrangement of the flowers of plants.

INFUSORIA.--A class of microscopic animalcules, so called from their havingoriginally been observed in infusions of vegetable matters. They consistof a gelatinous material enclosed in a delicate membrane, the whole or partof which is furnished with short vibrating hairs (called cilia), by meansof which the animalcules swim through the water or convey the minuteparticles of their food to the orifice of the mouth.

INSECTIVOROUS.--Feeding on insects.

INVERTEBRATA, or INVERTEBRATE ANIMALS.--Those animals which do not possessa backbone or spinal column.

LACUNAE.--Spaces left among the tissues in some of the lower animals andserving in place of vessels for the circulation of the fluids of the body.

LAMELLATED.--Furnished with lamellae or little plates.

LARVA (pl. LARVAE).--The first condition of an insect at its issuing fromthe egg, when it is usually in the form of a grub, caterpillar, or maggot.

LARYNX.--The upper part of the windpipe opening into the gullet.

LAURENTIAN.--A group of greatly altered and very ancient rocks, which isgreatly developed along the course of the St. Laurence, whence the name. It is in these that the earliest known traces of organic bodies have beenfound.

LEGUMINOSAE.--An order of plants represented by the common peas and beans,having an irregular flower in which one petal stands up like a wing, andthe stamens and pistil are enclosed in a sheath formed by two other petals. The fruit is a pod (or legume).

LEMURIDAE.--A group of four-handed animals, distinct from the monkeys andapproaching the insectivorous quadrupeds in some of their characters andhabits. Its members have the nostrils curved or twisted, and a clawinstead of a nail upon the first finger of the hind hands.

LEPIDOPTERA.--An order of insects, characterised by the possession of aspiral proboscis, and of four large more or less scaly wings. It includesthe well-known butterflies and moths.

LITTORAL.--Inhabiting the seashore.

LOESS.--A marly deposit of recent (Post-Tertiary) date, which occupies agreat part of the valley of the Rhine.

MALACOSTRACA.--The higher division of the Crustacea, including the ordinarycrabs, lobsters, shrimps, etc., together with the woodlice andsand-hoppers.

MAMMALIA.--The highest class of animals, including the ordinary hairyquadrupeds, the whales and man, and characterised by the production ofliving young which are nourished after birth by milk from the teats(MAMMAE, MAMMARY GLANDS) of the mother. A striking difference in embryonicdevelopment has led to the division of this class into two great groups; inone of these, when the embryo has attained a certain stage, a vascularconnection, called the PLACENTA, is formed between the embryo and themother; in the other this is wanting, and the young are produced in a veryincomplete state. The former, including the greater part of the class, arecalled PLACENTAL MAMMALS; the latter, or APLACENTAL MAMMALS, include theMarsupials and Monotremes (ORNITHORHYNCHUS).

MAMMIFEROUS.--Having mammae or teats (see MAMMALIA).

MANDIBLES.--in insects, the first or uppermost pair of jaws, which aregenerally solid, horny, biting organs. In birds the term is applied toboth jaws with their horny coverings. In quadrupeds the mandible isproperly the lower jaw.

MARSUPIALS.--An order of Mammalia in which the young are born in a veryincomplete state of development, and carried by the mother, while sucking,in a ventral pouch (marsupium), such as the kangaroos, opossums, etc. (seeMAMMALIA).

MAXILLAE.--in insects, the second or lower pair of jaws, which are composedof several joints and furnished with peculiar jointed appendages calledpalpi, or feelers.

MELANISM.--The opposite of albinism; an undue development of colouringmaterial in the skin and its appendages.

METAMORPHIC ROCKS.--Sedimentary rocks which have undergone alteration,generally by the action of heat, subsequently to their deposition andconsolidation.

MOLLUSCA.--One of the great divisions of the animal kingdom, includingthose animals which have a soft body, usually furnished with a shell, andin which the nervous ganglia, or centres, present no definite generalarrangement. They are generally known under the denomination of"shellfish"; the cuttle-fish, and the common snails, whelks, oysters,mussels, and cockles, may serve as examples of them.

MONOCOTYLEDONS, or MONOCOTYLEDONOUS PLANTS.--Plants in which the seed sendsup only a single seed-leaf (or cotyledon); characterised by the absence ofconsecutive layers of wood in the stem (endogenous growth), by the veins ofthe leaves being generally straight, and by the parts of the flowers beinggenerally in multiples of three. (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 aslightly 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 ashort body, with indistinct indications of a division into segments, andthree pairs of fringed limbs. This form of the common fresh-water CYCLOPSwas described as a distinct genus under the name of NAUPLIUS.

NEURATION.--The arrangement of the veins or nervures in the wings ofinsects.

NEUTERS.--Imperfectly developed females of certain social insects (such asants 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 drawnacross the eye in birds and reptiles, either to moderate the effects of astrong light or to sweep particles of dust, etc., from the surface of theeye.

OCELLI.--The simple eyes or stemmata of insects, usually situated on thecrown of the head between the great compound eyes.

OESOPHAGUS.--The gullet.

OOLITIC.--A great series of secondary rocks, so called from the texture ofsome of its members, which appear to be made up of a mass of small EGG-LIKEcalcareous bodies.

OPERCULUM.--A calcareous plate employed by many Molluscae to close theaperture of their shell. The OPERCULAR VALVES of Cirripedes are thosewhich 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 whichhave the seed straight.

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

OVA.--Eggs.

OVARIUM or OVARY (in plants).--The lower part of the pistil or female organof the flower, containing the ovules or incipient seeds; by growth afterthe other organs of the flower have fallen, it usually becomes convertedinto 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, andincluding the elephant, rhinoceros, hippopotamus, etc.

PALAEOZOIC.--The oldest system of fossiliferous rocks.

PALPI.--Jointed appendages to some of the organs of the mouth in insectsand Crustacea.

PAPILIONACEAE.--An order of plants (see LEGUMINOSAE), The flowers of theseplants are called PAPILIONACEOUS, or butterfly-like, from the fanciedresemblance 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 unimpregnatedeggs or seeds.

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

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

PELVIS.--The bony arch to which the hind limbs of vertebrate animals arearticulated.

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 oftrue leaves.

PIGMENT.--The colouring material produced generally in the superficialparts 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 thecentre of the other floral organs. The pistil is generally divisible intothe 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, likethe 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 ofnewly-germinated plants.

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

POLLEN.--The male element in flowering plants; usually a fine dust producedby the anthers, which, by contact with the stigma effects the fecundationof 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 othershermaphrodite. The unisexual (male and female) flowers, may be on the sameor on different plants.

POLYMORPHIC.--Presenting many forms.

POLYZOARY.--The common structure formed by the cells of the Polyzoa, suchas the well-known seamats.

PREHENSILE.--Capable of grasping.

PREPOTENT.--Having a superiority of power.

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

PROCESSES.--Projecting portions of bones, usually for the attachment ofmuscles, ligaments, etc.

PROPOLIS.--A resinous material collected by the hivebees from the openingbuds of various trees.

PROTEAN.--Exceedingly variable.

PROTOZOA.--The lowest great division of the animal kingdom. These animalsare composed of a gelatinous material, and show scarcely any trace ofdistinct organs. The Infusoria, Foraminifera, and sponges, with some otherforms, belong to this division.

PUPA (pl. PUPAE).--The second stage in the development of an insect, fromwhich it emerges in the perfect (winged) reproductive form. In mostinsects the PUPAL STAGE is passed in perfect repose. The CHRYSALIS is thepupal state of butterflies.

RADICLE.--The minute root of an embryo plant.

RAMUS.--One half of the lower jaw in the Mammalia. The portion which risesto articulate with the skull is called the ASCENDING RAMUS.

RANGE.--The extent of country over which a plant or animal is naturallyspread. RANGE IN TIME expresses the distribution of a species or groupthrough the fossiliferous beds of the earth's crust.

RETINA.--The delicate inner coat of the eye, formed by nervous filamentsspreading from the optic nerve, and serving for the perception of theimpressions produced by light.

RETROGRESSION.--Backward development. When an animal, as it approachesmaturity, becomes less perfectly organised than might be expected from itsearly stages and known relationships, it is said to undergo a RETROGRADEDEVELOPMENT or METAMORPHOSIS.

RHIZOPODS.--A class of lowly organised animals (Protozoa), having agelatinous body, the surface of which can be protruded in the form ofroot-like processes or filaments, which serve for locomotion and theprehension 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 ofchisel-like cutting teeth in each jaw, between which and the grinding teeththere is a great gap.

RUBUS.--The bramble genus.

RUDIMENTARY.--Very imperfectly developed.

RUMINANTS.--The group of quadrupeds which ruminate or chew the cud, such asoxen, sheep, and deer. They have divided hoofs, and are destitute of frontteeth in the upper jaw.

SACRAL.--Belonging to the sacrum, or the bone composed usually of two ormore united vertebrae to which the sides of the pelvis in vertebrateanimals are attached.

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

SCUTELLAE.--The horny plates with which the feet of birds are generallymore 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 animalor annelid is composed.

SEPALS.--The leaves or segments of the calyx, or outermost envelope of anordinary 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 tothe earlier part of the Palaeozoic series.

SPECIALISATION.--The setting apart of a particular organ for theperformance of a particular function.

SPINAL CORD.--The central portion of the nervous system in the Vertebrata,which descends from the brain through the arches of the vertebrae, andgives off nearly all the nerves to the various organs of the body.

STAMENS.--The male organs of flowering plants, standing in a circle withinthe petals. They usually consist of a filament and an anther, the antherbeing the essential part in which the pollen, or fecundating dust, isformed.

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 theleaves in many plants.

STYLE.--The middle portion of the perfect pistil, which rises like a columnfrom 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 theskull is composed.

TARSUS (pl. TARSI).--The jointed feet of articulate animals, such asinsects.

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 touchpossessed by many of the lower animals.

TERTIARY.--The latest geological epoch, immediately preceding theestablishment of the present order of things.

TRACHEA.--The windpipe or passage for the admission of air to the lungs.

TRIDACTYLE.--Three-fingered, or composed of three movable parts attached toa common base.

TRILOBITES.--A peculiar group of extinct crustaceans, somewhat resemblingthe woodlice in external form, and, like some of them, capable of rollingthemselves up into a ball. Their remains are found only in the Palaeozoicrocks, and most abundantly in those of Silurian age.

TRIMORPHIC.--Presenting three distinct forms.

UMBELLIFERAE.--An order of plants in which the flowers, which contain fivestamens and a pistil with two styles, are supported upon footstalks whichspring from the top of the flower stem and spread out like the wires of anumbrella, so as to bring all the flowers in the same head (UMBEL) nearly tothe 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 animalkingdom, so called from the presence in most cases of a backbone composedof numerous joints or VERTEBRAE, which constitutes the centre of theskeleton and at the same time supports and protects the central parts ofthe nervous system.

WHORLS.--The circles or spiral lines in which the parts of plants arearranged upon the axis of growth.

WORKERS.--See neuters.

ZOEA-STAGE.--The earliest stage in the development of many of the higherCrustacea, so called from the name of ZOEA applied to these young animalswhen they were supposed to constitute a peculiar genus.

ZOOIDS.--In many of the lower animals (such as the Corals, Medusae, etc.)reproduction takes place in two ways, namely, by means of eggs and by aprocess of budding with or without separation from the parent of theproduct 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 formproduced between two sexual reproductions; and these forms, which areapparently individual animals, have been called ZOOIDE.