  Zoology is that branch of Natural History which treats of animals, and embraces not only their structure and functions, their habits, instincts, and utility, but their names and systematic arrangement. Various systems have been proposed by different naturalists for the scientific arrangement of the animal kingdom, but that of Cuvier, with some modifications, is now thought the best, and a sketch of it will be found under the head of the Modern System in this Introduction. As, however, the System of LinnÆus was formerly in general use, and is still often referred to, it has been thought advisable to give a sketch of it first; that the reader may be aware of the difference between the old system and the new one. LINNÆAN SYSTEM.According to the system of LinnÆus, the objects comprehended within the animal kingdom were divided into six classes: Mammalia or Mammiferous Animals, Birds, Amphibia or Amphibious Animals, Fishes, Insects, and Worms, which were thus distinguished: Classes.
ORDERS OF MAMMALIA.The first class, or Mammalia, consists of such animals as produce living offspring, and nourish their young ones with milk supplied from their own bodies; and it comprises both the quadrupeds and the cetacea. This class was divided by LinnÆus into seven Orders: viz. primates, bruta, ferÆ, glires, pecora, belluÆ, and cetacea (this order was called Cete by LinnÆus) or whales. The characteristics of these were founded, for the most part, on the number and arrangement of the I. Primates.—Having the upper front teeth, generally four in number, wedge-shaped, and parallel; and two teats situated on the breast, as the apes and monkeys. II. Bruta.—Having no front teeth in either jaw; and the feet armed with strong hoof-like nails, as the elephant. III. FerÆ.—Having in general six front teeth in each jaw; a single canine tooth on each side in both jaws; and the grinders with conic projections, as the dogs and cats. IV. Glires.—Having in each jaw two long projecting front teeth, which stand close together; and no canine teeth in either jaw, as the rats and mice. V. Pecora.—Having no front teeth in the upper jaw; six or eight in the lower jaw, situated at a considerable distance from the grinders; and the feet with hoofs, as cattle and sheep. VI. BelluÆ.—Having blunt wedge-shaped front teeth in both jaws; and the feet with hoofs, as horses. VII. Cetacea.—Having spiracles or breathing-holes on the head; fins instead of fore feet; and a tail flattened horizontally, instead of hind feet. This order consists of the narvals, whales, cachalots, and dolphins. ORDERS OF BIRDS.The second class, or Birds, comprises all such animals as have their bodies clad with feathers. Their jaws are elongated, and covered externally with a horny substance, called a bill or beak, which is divided into two parts called mandibles. Their eyes are furnished with a thin, whitish, and somewhat transparent membrane, that can at pleasure be drawn over the whole external surface like a curtain. Their organs of motion are two wings and two legs; and they are destitute of external ears, lips, and many other parts which are important to quadrupeds. That part of Zoology which treats of Birds is called Ornithology. LinnÆus divided this class into six Orders: 1. Land Birds.I. Rapacious Birds (Accipitres).—Having the upper mandible hooked, and an angular projection on each side near the point, as the eagles, hawks, and owls. II. Pies (PicÆ).—Having their bills sharp at the edge, somewhat compressed at the sides, and convex on the top, as the crow. III. Passerine Birds (Passeres).—Having the bill conical and pointed, and the nostrils oval, open, and naked, as the sparrow and linnet. IV. Gallinaceous Birds (GallinÆ).—Having the upper mandible arched, and covering the lower one at the edge, and the nostrils arched over with a cartilaginous membrane, as the common poultry. 2. Water Birds.V. Waders (GrallÆ).—Having a roundish bill, a fleshy tongue, and the legs naked above the knees, as the herons, plovers, and snipes. VI. Swimmers (Anseres).—Having their bills broad at the top, and covered with a soft skin, and the feet webbed, as ducks and geese. ORDERS OF AMPHIBIA.Under the third class, or Amphibia, LinnÆus arranged such animals as have a cold, and, generally, naked body, a lurid colour, and nauseous smell. They respire chiefly by lungs, but they have the power of suspending respiration for a long time. They are extremely tenacious of life, and can repair certain parts of their bodies which have been lost. They are also able to endure hunger, sometimes even for months, without injury. The bodies of some of them, as the turtles and tortoises, are protected by a hard and horny shield or covering; those of others are clad with scales, as the serpents, and some of the lizards; whilst others, as the frogs, toads, and most of the water-lizards, are entirely naked, or have their skin covered with warts. Many of the species shed their skins at certain times of the year. Several of them are furnished with a poison, which they eject into wounds that are made by their teeth. They chiefly live in retired, watery, and marshy places; and, for the most part, feed on other animals, though some of them eat water-plants, and many feed on garbage and filth. None of these species chew their food; they swallow it whole, and digest it very slowly. The offspring of all these animals are produced from eggs, which, after they have been deposited by the parent animals in a proper place, are hatched by the heat of the sun. The eggs of some of the species are covered with a shell; those of others have a soft and tough skin or covering, not much unlike wet parchment; and the eggs of several are perfectly gelatinous. In those few that produce their offspring alive, as the vipers and some other serpents, the eggs are regularly formed, but are hatched within the bodies of the females. This class LinnÆus divided into three Orders: I. Reptiles.—Having four legs, and walking with a crawling pace, as the tortoises, toads, and lizards. II. Serpents.—Having no legs, but crawling on the body. III. Nantes.—Living in the water, furnished with fins, and breathing by means of gills. These are true Fishes, principally of the group termed Chondropterygii, or Cartilaginous Fishes, by Cuvier. ORDERS OF FISHES.Fishes constituted LinnÆus’s fourth class of animals. They are all inhabitants of the water, in which they move by certain organs called fins. Those situated on the back are called dorsal fins; those on the sides, behind the gills, pectoral fins; those below the body, near the head, are ventral; those behind the vent are anal; and that which forms the tail is called the caudal fin. Fishes breathe by gills, which, in most species, are situated at the sides of the head. Fishes rise and sink in the water, generally by a kind of bladder in the interior of the body, called an air-bladder. Some of them do not possess this organ, and consequently are seldom found but at the bottom of the sea, from which they can only rise by an effort. The bodies of these animals are usually covered with scales, which keep them from injury by the contact of the water. The fishes were divided by LinnÆus into four Orders: I. Apodal.—Having no ventral fins, as the eel. II. Jugular.—Having the ventral fins situated in front of the pectoral fins, as the cod, haddock, and whiting. III. Thoracic.—Having the ventral fins situated directly under the pectoral fins, as the perch and mackerel. IV. Abdominal.—Having the ventral fins on the lower part of the body below the pectoral fins, as the salmon, herring, and carp. ORDERS OF INSECTS.The fifth class of LinnÆus comprised the Insects; and the branch of Zoology which treats of them is called Entomology. Nearly all insects go through certain great changes at different periods of their existence. From the egg is hatched the larva, which is a grub or caterpillar, and destitute of wings; this afterwards changes to a pupa, or chrysalis, wholly covered with a hard shell, or strong skin, from which the perfect or winged insect bursts forth. Spiders and their allies, which were included by LinnÆus in the insects, issue from the egg in nearly a perfect state. LinnÆus divided his class of insects into seven Orders: I. Coleopterous.—Having elytra, or crustaceous cases covering the wings; and which, when closed, meet in a straight line along the middle of the back, as the cockchafer. II. Hemipterous.—Having four wings, the upper ones partly crustaceous, and partly membranous; not divided straight down the middle of the back, but crossed, or incumbent on each other, as the cockroach. III. Lepidopterous.—Having four wings covered with fine scales almost like powder, as the butterflies and moths. IV. Neuropterous.—Having four membranous and semi-transparent wings, veined like network; and the tail without a sting, as the dragon-fly and ephemera. V. Hymenopterous.—Having four membranous and semi-transparent wings, veined like network; and the tail armed with a sting, as the wasp and bee. VI. Dipterous.—Having only two wings, as the common house-flies. VII. Apterous.—Having no wings, as the spiders. ORDERS OF VERMES, OR WORMS.The sixth and last LinnÆan class consisted of Worms, or Vermes. These are slow of motion, and have soft and fleshy bodies. Some of them have hard internal parts, and others have crustaceous coverings. In some of the species, eyes and ears are very perceptible, whilst others appear to enjoy only the senses of taste and touch. Many have no distinct head, and most of them are destitute of feet. They are, in general, so tenacious of life, that parts which have been destroyed will be reproduced. These animals are principally distinguished from those of the other classes by having tentacula, or feelers, and are divided by LinnÆus into five Orders: I. Intestina.—Are simple and naked, without limbs; some of them live within other animals, as the ascarides and tape-worms; others in water, as the leeches; and a few in the earth, as the earth-worm. II. Mollusca.—Are simple animals, without shells, and furnished with limbs, as the cuttle-fish, medusa, star-fish, and sea-urchin. III. Testacea.—Are animals similar to the last, but covered with shells, as oysters, cockles, snails, and limpets. IV. Lithophyta.—Are composite Polyps, dwelling in cells in a calcareous base which they produce, as corals and madrepores. V. Zoophyta.—Are usually composite animals, but do not reside in stony cells. The coral, sponge, and polyps are instances of this order, which also includes the Infusorial Animalcules. MODERN SYSTEM.It will be found by reading the following sketch of the Modern System that the greatest change has taken place in the latter two classes. The others remain nearly the same in effect, though their distinctions are different, and the classes are not arranged in the same order. According to Cuvier, all animals are arranged in four great divisions, which are subdivided into classes and orders, as follows:—
THE VERTEBRATED ANIMALSHave a backbone divided into vertebrÆ or joints, whence they take their name. They have also separate senses for hearing, seeing, tasting, smelling, and feeling; a distinct head, with a mouth opening by two horizontal jaws; a muscular heart, and red blood. The four classes of Vertebrata and their orders are as follow:— I. The Mammalia are all furnished with mammÆ, or teats, through which they give milk to their young, which they bring forth alive. They have warm blood, which all circulates from the heart through the lungs, and returns to the heart before it passes through the body. Their skins are naked, or covered with wool or hair, and their mouths are generally furnished with teeth. There are eleven orders, which are thus distinguished:— Section I.—Unguiculated Animals, or Mammalia having Nails or Claws.I. Bimana, or two-handed. This order contains only the human species. II. Quadrumana, or four-handed. This order contains the apes, baboons, and monkeys, and the lemurs. III. Cheiroptera, the bat family. IV. Carnivora, or beasts of prey. This order is divided into the following three tribes:— 1. The Insectivora, consisting of those animals which live upon insects, as the hedgehog, the shrew, and the mole. 2. The Carnivora proper, consisting chiefly of the cat family, including lions, tigers, and their allies; the bear family, including the badger, the coati-mondi, the racoon, &c.; the dog family, including the wolf and the fox; the weasel family; the civet-cats; and the hyÆna. 3. The Amphibia, consisting of the seals, and other allied animals. V. Marsupialia, including the opossums and the kangaroos. VI. Monothrema, containing the Echidna and Ornithorhynchus of Australia. VII. Rodentia, or gnawing animals. The principal of these are the squirrel family, mice and rats, hares and rabbits, the beaver, the porcupine, and the guinea-pig. VIII. Edentata, or toothless animals, that is, without front teeth. The principal of these are the sloths, the armadillos, and the ant-eaters. Section II.—Ungulated or Hoofed Mammalia.IX. Pachydermata, or thick-skinned animals. The principal of these are the elephant, the hippopotamus, the rhinoceros; the horse family, including the ass, the mule, the zebra, and the quagga; the wild boar family, and the tapir. X. Ruminantia, or ruminating animals, the principal of which are the camel family, the deer family, the giraffe, the antelope family, the goat family, the sheep family, and the ox family. Section III.—Aquatic Mammalia, having no Hind Limbs, and the Fore Limbs converted into Fins. XI. Cetacea, or sea mammalia, the principal of which are the whale family, the dolphin family, the manati, the porpoise family, and the narwhal, or sea-unicorn. THE AVES, OR BIRDS,Lay eggs from which their young are hatched by what is called incubation. Their skins are covered with feathers; and their jaws are horny, without teeth. Their blood is warm, and circulates like that of the mammalia. The six orders of Aves are as follow:— 1. Raptores, or birds of prey. These birds are distinguished by a very strong and sharp bill more or less curved, but always hooked at the extremity of the upper mandible, which is covered at the base with a kind of skin called the cere. The nostrils are usually open. The legs are very strong, the feet are large, and the toes, which are four in number, are armed with very strong, sharp, curved claws. The principal raptorial birds are the vultures, including the condor; the falcon family, including the eagles, hawks, kites, and buzzards; and the owls. 2. Insessores, or perching birds. These birds have all feet formed for perching, the hind toe springing from the same place as the other toes, which gives them great power of grasping. Their legs are of moderate length, and their claws not sharply curved. This order includes the thrushes, nightingales, and all the finest songsters of our groves, with the robin-redbreast, the sparrow, and other birds seen about dwellings, the swallows, the larks, the crow family, the kingfishers, the birds of paradise, and the humming birds. 3. Scansores, or climbers. These birds have two toes before and two behind. This construction gives them such great power of climbing, that they can ascend the perpendicular trunk of a tree. The principal birds in this order are the parrots, the cuckoos, and the woodpeckers. 4. Rasores, or gallinaceous birds. These birds have the head small in proportion to the body. The bill is generally short, with the upper mandible somewhat curved. The nostrils have usually a protecting fleshy membrane. The tarsus, or lower part of the leg, is long and bare, and there are four toes, those in front being united by a slight membrane, while that behind is generally higher up the leg, and smaller than the others. This order comprises most of the birds used as food, and includes the peacock, the turkey, the common cock and hen, the partridge, the pheasant, and the pigeon family. 5. Grallatores, or Waders. These birds are characterised by their long and slender legs, and by the thighs being more or less bare. There are three anterior toes, more or less united at the base by a membrane, or rudimentary web. The hind toe is wanting in some members of the order. This order contains the ostrich family, the bustards and plovers; the cranes, herons, and storks; and the snipes and woodcocks. 6. Palmipedes, or web-footed birds. These birds have the legs and feet short, and placed behind, with their fore toes united by a thick and strong membrane. The neck is much longer than the legs, and their bodies are covered with a dense layer of down beneath the outer plumage, which is close, and imbued with an oily fluid that repels the water. The principal birds in this order are the grebes, the auks and penguins, the petrels, the pelican and cormorant and the swans, ducks, and geese. By many ornithologists the pigeons and ostriches are considered to form distinct orders, called respectively ColumbÆ and Cursores. THE REPTILIA,Or Reptiles, have neither hair, wool, nor feathers, and their bodies are either naked, or covered with scales. Some lay eggs, and some bring forth their young alive. Some have gills, and others lungs, but the latter have only a portion of the blood passing through them; and thus the blood of reptiles is cold, as it is respiration which gives the blood heat. The senses of reptiles are dull, and their movements are either slow or laborious. The following are the four orders into which this class is divided:— 1. Chelonian Reptiles. These animals have four legs. The body is enclosed in an upper buckler, called the carapace, and an under one, called the plastron. They have lungs which are much expanded; but they have no teeth, though they have hard horny jaws. The females lay eggs covered with a hard shell. The principal animals belonging to this division are the tortoises, which live on land or in fresh waters, and the turtles, which inhabit the sea. 2. The Saurian Reptiles. These animals have also expanded lungs, and generally four legs, but some have only two. Their bodies are covered with scales, and their mouths filled with teeth. This order includes all the crocodiles and lizards. The crocodiles have broad flat tongues, attached throughout to the jaws, and the lizards have long narrow tongues, which many of them can extend to a great distance from the mouth. 3. The Ophidian Reptiles are the snakes and serpents. The body is covered with scales, but it is destitute of feet. The lungs are generally well developed, only on one side. Serpents are frequently furnished with poison-bags at the base of some of their teeth. 4. The Batrachian Reptiles include the frogs and toads. The body is naked. The greater part of these reptiles undergo a transition from a fish-like tadpole furnished with gills to a four-legged animal with lungs. Others never lose their gills, though they acquire lungs, and of this kind are the siren and the proteus. THE PISCES,Or Fishes, are defined by Cuvier to be vertebrated animals with red blood, breathing through the medium of water by means of their branchiÆ or gills. To this definition may be added, that fishes have no neck, and that the body generally tapers from the head to the tail; that most of the species are furnished with air-bladders which enable them to swim; and that their bodies are generally covered with scales. The heart has only one auricle, and the blood is cold. The gills require to be kept moist to enable the fish to breathe, and as soon as they become dry, the fish dies. Thus fishes with large gill openings die almost as soon as they are taken out of the water; while those with very small openings, like the eel, live a long time. Fishes have no feet, but are furnished with fins. The scientific knowledge of Fishes is called Ichthyology. Fishes are first divided into two great series, viz. the Bony Fishes, and the Cartilaginous Fishes, and these are again subdivided into nine orders, as follows:— Osseous or Bony Fishes.1. Acanthopterygii, or fishes with hard fins. 2. Malacopterygii abdominales, or soft-finned fishes, with the ventral fins on the abdomen behind the pectorals. 3. Malacopterygii sub-brachiati, or soft-finned fishes, with the ventral fins under the gills. 4. Malacopterygii apodes, or soft-finned fishes, without ventral fins. 5. Lophobranchii, or fishes with tufted gills. 6. Plectognathii, or fishes with the upper jaw fixed. Chondropterygii, or Cartilaginous Fishes. 7. Cyclostomi, or fishes with jaws fixed in an immovable ring, and with holes for the gills. 8. Selachii, or fishes with movable jaws and holes for the gills. 9. Sturiones, with the branchiÆ in the usual form. Of the bony fishes the Acanthopterygii, or fishes with hard spiny fins, are divided into fifteen families, the principal of which are the perch family, the mailed cheek fishes, including the gurnards, the flying fish of the Mediterranean, and the sticklebacks, or jack banticles; the mackerel family, including the tunny, bonito, and sword-fish; the pilot-fish, the dolphin of the Mediterranean, so celebrated for the beauty of its dying tints, and the John Dory. Among the Malacopterygii abdominales, or soft-finned fishes, that have their ventral fins suspended from the abdomen, the most interesting are the carp family, the pike family, the flying-fish of the ocean, the salmon family, and the herring family, including the sprat, pilchard, and anchovy. The Malacopterygii sub-brachiati are soft-finned fishes, with the ventral fins beneath the pectorals; the principal of which are the cod family, including the haddock, whiting, and ling; the flat-fish family, including soles, turbots, plaice, and flounders; and the suckers or lump-fish. The Malacopterygii apodes are confined to the eel family. The Lophobranchii include the pipe fish, and other fishes of similar form. The Plectognathi comprise the very singular forms of the balloon-fish, the sun-fish, and other similar fishes. The Chondropterygii, or Cartilaginous fishes, are divided into three orders, viz. the Sturiones, or sturgeon family; the Selachi, or sharks and rays, including the torpedo; and the Cyclostomi, or lamprey family. The last two orders were included by Cuvier in a single one. THE MOLLUSCOUS ANIMALSHave no bones except their shells. Their sense of feeling appears to be very acute, but the organs for the other senses are either wanting or very imperfect. The blood is cold and white, and the heart often consists of only one ventricle; a few of them have imperfect lungs, but the greater number breathe through gills. They have all the power of remaining a long time in a state of rest, and their movements are either slow or violently laborious. Some of them appear incapable of locomotion. They produce their young from eggs, but some lay their eggs on a part of their own body, where the young are hatched. The following are Cuvier’s six classes:— 1. Cephalopoda, or Head-footed Mollusca. These animals are furnished with long fleshy arms or feet, proceeding from the head, which is not distinct from the body, and on which they crawl. There is only one order, which includes the cuttle-fish, nautilus, and belemnites. 2. Pteropoda, or Wing-footed Mollusca. These animals have two membranous feet or arms, like wings, proceeding from the neck. There is only one order, which contains six genera, the best known of which is the HyalÆa, the shell of which is commonly called Venus’s chariot. 3. Gasteropoda, or Body-footed Mollusca. All these animals crawl with the flat part of the body, which acts as a kind of sucker. There are nine orders in Cuvier’s system. The common snail will give an idea of the habits of the class. 4. Acephala, or Headless Mollusca. These animals have no apparent head, and breathe by means of branchiÆ, which are generally ribbon-shaped. Most of them are enclosed in a bivalve shell, but some are naked; the former are the Testacea of Cuvier, and the Conchifera of Lamarck; the latter are the Tunicata of Lamarck. They form two orders. 5. Brachiopoda, or Arm-footed Mollusca. These animals also have a bivalve shell; but they have no true branchiÆ, and their respiration is effected by the agency of the mantle. They have two spiral arms. 6. Cirrhopoda, or Curled-footed Mollusca. These are generally attached, and enclosed in a shell of several pieces; they are furnished with a mouth, armed with jaws, and with several pairs of jointed and fringed organs, called cirri, by the protrusion and retraction of which they capture their prey. Examples of this class are the Barnacles and Acorn shells. These animals have long ceased to be regarded as Mollusca, the investigations of modern naturalists having proved them to be true articulated animals most nearly related to the Crustacea. THE ARTICULATED ANIMALSHave no back-bone. The covering of the body is sometimes hard and sometimes soft, but it is always divided into segments by a number of transverse incisions. The limbs, when the body is provided with any, are jointed; and they can be separated from the body without any serious injury being sustained by the animal, new limbs being shortly after formed to replace them. The senses of tasting and seeing are more perfect than those of the Mollusca, though that of feeling seems much less acute. In other respects the four classes differ considerably from each other. [The Entozoa, or Intestinal Worms, placed by Cuvier and others among the Radiata, are now arranged amongst the lowest forms of articulated animals, as are also those animalcules known as Rotifera.] I. The Annelida, or Red-blooded Worms, have no heart, properly so called, but have sometimes one or more fleshy ventricles. They breathe through branchiÆ. Their bodies are soft, and more or less elongated, being divided into numerous rings or segments. The head, which is at one extremity of the body, can scarcely be distinguished from the tail, except by having a mouth. These animals have no feet, properly so called, but they are furnished with little fleshy projections, bearing tufts of hairs or bristles, which enable them to move. They are generally of carnivorous habits. They lay eggs, but the young are frequently hatched before exclusion, and hence these creatures are said to be ovoviviparous. Their study is called Helminthology. As examples of the three orders of this class may be mentioned the serpulÆ or worm-like animals, often found on shells, the common earthworm, and the leech family. II. The Crustacea comprise the shell-fish commonly called crabs, lobsters, shrimps, and prawns. They have a distinct head, furnished with antennÆ, eyes, and mouth; and their bodies are Section I. Malacostraca.Shell solid, legs ten or fourteen, foot-jaws six or ten, mandibles two, maxillÆ four; mouth with a labrum. Sub-section I. Podophthalma, eyes on foot-stalks. Order 1. Decapoda, legs ten. Sub-order 1. Brachyura, the crabs. Sub-order 2. Macroura, the lobsters. Order 2. Stomapoda, legs more than ten. Sub-section II. Edriophthalma, eyes not on foot-stalks. Order 3. Amphipoda, body compressed; mandibles palpigerous. Order 4. LÆmodipoda, abdomen rudimental, with only the rudiments of one or two pairs of appendages. Order 5. Isopoda, body depressed; abdominal appendages flat; mandibles not palpigerous. Section II. Entomostraca.Shell not solid; legs variable in number; mouth variable. Order 6. Branchiopoda. Integuments horny, branchiÆ feathery, forming part of the feet. It is to this division of the Crustacea that the Cirrhopoda are now referred. Order 7. PÆcilopoda, mouth suctorial. Sub-order 1. Xiphosura, or king-crabs. Sub-order 2. Siphonostoma, or fish parasites. III. The Arachnida are defined by Lamarck to be oviparous animals, provided with six or more articulated legs, not subject to metamorphosis, and never acquiring any new kinds of organs. It is now known, however, that some mites undergo a sort of metamorphosis, having only six legs when first hatched, and passing through a quiet pupa stage before acquiring their perfect form. Their respiration is either by means of air-sacks, which serve for lungs, or of a kind of tube with circular openings for the admission of air. There is a rudimentary heart and circulation in most of the species. There are two orders; those with lungs, and those without. Order I. PulmonariÆ. The Arachnides comprised in this division have air-sacks, which serve for lungs, a heart with distinct vessels, and from six to eight simple eyes. There are two Order II. TracheariÆ. These Arachnides are distinguished by their respiratory organs, which consist of radiated or branched tracheÆ, receiving air by two circular openings. Their eyes vary from two to four. The principal animals belonging to this division are the long-legged spiders (Phalangium), and the mites (Acarus), including the gardener’s pest, the little red spider (Acarus telarius), the cheese mite (Acarus Siro), and the harvest bug (Acarus or Leptus autumnalis). IV. The Insecta form the fourth and last class of articulated animals, and they derive their name from the Latin word insectum, which signifies “cut into,” in allusion to the distinct divisions of head, thorax, and abdomen in the true insects: and in contradistinction to the Annelides, the bodies of which present no such divisions. The true insects are defined as animals without vertebrÆ, possessing six feet, with a distinct head furnished with antennÆ, and breathing through stigmatic openings, which lead to interior tracheÆ. The Myriapoda have, however, more feet. The following are the twelve orders into which this class is divided. Section I. Insects undergoing Metamorphosis.1. Coleoptera (from two Greek words signifying sheathed wings). These are the beetles, which are all furnished with membranous wings, with which they fly, and which are protected by horny upper wings, or wing-cases, called elytra. They are all masticators, and are all provided with mandibles or projecting jaws, and maxillÆ. 2. Orthoptera, or straight-winged insects. This order comprises the crickets, grasshoppers, locusts, and similar insects. They have their upper wings of the consistence of parchment, and have mandibles and maxillÆ. 3. Hemiptera, or half-winged insects, have frequently half the upper wing membranous, like the under ones, while the other half is leathery. To this division belong the bugs, the water-scorpions, the cicadÆ or froghoppers, and the aphides. These insects have neither mandibles nor maxillÆ, but in their place have a sheath and sucker. 4. Neuroptera, or nerved-winged insects, such as the dragon-flies, have both pairs of wings membranous, naked, and finely reticulated. The mouth is adapted for mastication, and furnished with mandibles and maxillÆ. 5. Hymenoptera, membranous winged insects, such as bees, wasps, ichneumon flies, &c. All the four wings are membranous, but they have fewer nervures, and are not reticulated like those of the preceding order. The mouth is furnished with mandibles and maxillÆ, and the abdomen is terminated either by an ovipositor or a sting. 6. Lepidoptera, or scaly-winged insects. These are the butterflies and moths, which are characterised by the farinaceous or scaly aspect of their wings, and the tubular or thread-like extension of the parts of the mouth. 7. Strepsiptera or Rhipiptera, with twisted wings. These creatures resemble the ichneumon, in laying their eggs in the bodies of other insects, though they generally attack wasps and bees. The principal genera are Xenos and Stylops. They are generally considered to be closely allied to the Beetles. 8. Diptera, or two-winged insects, including the flies. The mouth is furnished with a proboscis, and there are two small wings called halteres placed behind the true wings, which act as balancers. 9. Suctoria, or sucking insects, such as the flea, which have no wings, but are furnished with an apparatus for sucking blood. Section II. Insects not undergoing Metamorphosis.10. Thysanoura, or spring-tail insects. These creatures are of small size, and without wings; they are found in crevices of woodwork, or under stones. The principal genera are Lepisma and Podura. 11. Parasita, or parasitical insects, such as the louse. They are also without wings. 12. Myriapoda. This order is made a separate class by many naturalists, as the creatures contained in it are distinguished from the true insects by the great number of their feet; by the want of distinct divisions into thorax and abdomen; and by the great number of segments into which the body is divided. The principal insects in this order are included in the LinnÆan genera Julus and Scolopendra, commonly called centipedes. The term larva is applied to the young of all insects, included in the first nine orders, when first hatched. The different kinds have, however, other names; that is to say, the larva of a butterfly, or moth, is called a caterpillar; that of a beetle, a grub; and that of a fly, a maggot. The larva changes its skin several times, and at last goes into the pupa state, when it is called a chrysalis, an aurelia, or a nymph. Sometimes the pupa is wrapped up in a loose outer covering called a cocoon. From the pupa in time bursts forth the imago, or perfect insect. The Apterous, or wingless true insects, and the Myriapoda, which are also without wings, do not undergo any metamorphosis. THE RADIATED ANIMALSAre so called because their organs of locomotion, and even their internal viscera, are generally arranged in a circle round a centre, so as to give a radiated appearance to the whole body. The animals included in this class are the very lowest in the scale; they have scarcely any external senses; their movements are slow, and almost their only sign of life is a craving for food. Some of them, however, have a distinct mouth and alimentary canal, with an anal orifice; others have a bag-like stomach with a kind of mouth, through which they both take their food and reject their excrements; while others have no mouth, and appear only to absorb nourishment through pores. In the like manner, though some are oviparous, others may be propagated by division into plants. Of these Cuvier makes five classes: I. Echinodermata, or sea-urchins. These animals have a leathery or crustaceous skin or shell, commonly covered with numerous tubercles. The mouth is generally in the centre of the animal, and is often armed with five or more pieces of bone, which serve as teeth; the stomach is a loose bag; the organs for respiration are vascular; and the animals are oviparous. They are furnished with tentacular tubes, which serve as arms or feet, and which they can push out and draw back at pleasure; and they have yellowish or orange-coloured blood, which appears to circulate. Cuvier divides this class into those with feet, and those without; but Lamarck, whose arrangement has been more generally followed, divides them into three orders; viz.: 1. The Fistuloides, or Holothurida, which have cylindrical bodies, leathery skins, and mouths surrounded by tentacula. These creatures live in the sea, or in the sands on the sea-shore; the trepang, or eatable worm of the Chinese, is one of them. 2. The Echinides. These are the sea-urchins, properly so called, and the shells, when the animals are out of them, are called sea-eggs. The Echinides live in the sea. They lay eggs, and the roe, or imperfect eggs, occupy a large portion of the space within the shell when the animal is still alive. 3. The Stellerides, or Asterias, are the star-fish. The mouth in these creatures is in the middle of the lower surface, and it has a membranous lip, capable of great dilation, but furnished with angular projections for capturing its prey. The skin is soft, but leathery, and it is covered on the back with spongeous tubercles, or scales. The rays are hollow beneath, and furnished with tentacula, by the aid of which the star-fish manages to crawl backwards, forwards, or sideways, as the case may be, any of the rays serving as a leader. These animals are found on the sea-shore, forming large beds, which are washed over by the sea. The Crinoidea, or stone-lilies, of which such curious fossil specimens have been found, are nearly allied to the star-fish. II. The Intestina, or Entozoa. The intestinal worms were divided into two kinds by Cuvier, viz. the Cavitaires, including the worms of children, and other cylindrical worms; and the Parenchymateux, or flat worms; such as the fluke in sheep and the tape-worm in human beings. The Entozoa are now universally regarded as belonging to the Articulated or Annulose division of the animal kingdom. III. AcalephÆ, or Sea-Jellies. These creatures are of a soft and jelly-like substance, with a thin skin, and an unarmed mouth. The Medusides are very numerous, and produce that beautiful phosphorescent light noticed by voyagers in the Australian seas. The most interesting of the Acalephes is the Portuguese man-of-war, or Physalia. IV. Polyps, or Anthozoa, according to Cuvier, were divided into three orders; namely: 1. Fleshy Polyps (Sea anemones); 2. Gelatinous Polyps (Hydra); and 3. Polyps with Polyparies, the latter including all the various compound zoophytes, with the Sponges. Of these the FlustrÆ, or Sea Mats, and numerous allied species, have since been recognised 1. Helianthoida. This order includes the actinia, or sea-anemone; and the madrepores, sea-mushrooms, and brainstones, which live in communities, and possess the power of secreting calcareous matters, which they emit to form these stony substances. 2. Asteroida. Some of the animals belonging to this division are called sea-pens, and others form some of the different kinds of coral, particularly that used for necklaces, &c. 3. Hydroida. This order includes the fresh-water polypi, which, it is well known, by the experiments that have been tried, may be cut in pieces and even turned inside out without destroying life. It must be observed that the contents of this group in Cuvier’s system consisted of all those forms of animals which he could not, in accordance with the knowledge possessed in his day, conveniently place anywhere else. Within the last few years, however, great progress has been made in the arrangement of the animals placed in this group by Cuvier. One of the most important changes has been the establishment of a fifth group of animals for the Infusoria and Sponges, together with certain other creatures of very low organisation. To these the name of Protozoa has been given. The Entozoa have been removed amongst the articulate animals, and there is a growing conviction that the Echinodermata will have to be transferred to the same section. There remain, consequently, the AcalephÆ and Polyps of Cuvier, which form a group characterised by their soft and generally gelatinous texture; by the existence of peculiar cells, called thread cells, in the skin; and by their possession of an alimentary cavity with only a single orifice. To these the name of Coelenterata has been given. They are divided into two classes: I. The Anthozoa, or Polyps, including the orders Helianthoida and Asteroida; and II. The Hydrozoa, composed of the Hydroid Polyps and AcalephÆ, the connection between which, as indicated in the text (p. 609), is very intimate. V. The Infusoria, or Animalcula, are so small as to be invisible to the naked eye, and they are all inhabitants of liquids. Cuvier arranged them in two orders, one of which he called Les RotifÈres, and the other Les Infusories homogÈnes, but the first of these divisions is now included among the Articulata. The remainder of the Infusoria of Cuvier, with the exception of some which are now known to be of vegetable nature, are arranged, with the Sponges and some other animals, in a separate division, called Protozoa, the classification of which is still in a somewhat uncertain state. The three principal classes are those of the Infusoria, the Sponges, and the Rhizopoda; but there are other forms which will not admit of being brought under any of these denominations. Nearly all the Protozoa are microscopic, except when, as in the case of the Sponges, they form an aggregation of individuals. They are very numerous, and, although exceedingly simple in their structure, their history often possesses much interest. |
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