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All the shell-animals are of such a constitution as perpetually to secrete or exude from their bodies a viscid moisture, and it is with this, managed according to the exigencies of the animal, that the shell is, throughout life, increased in dimensions, and repaired when accidently broken in any particular part. The growth of shells proceeds from the edges of the mouth or opening, and thus the spires or turns of the univalve shells are gradually increased in number and size, till the aniinal has arrived at its full growth. The bivalves are increased in a similar manner, by the gradual enlargement of the outline of each valve. The priucipal genera in the UNIVALVES are, 1. Argonuutu. 2. Nautilus, pearly-nautilus. 3. Helix, snail. 4. Dentalium, tooth-fish. 5. Serpula. 6. Teredo, ship-worin. 7. Subellu. 8. Patella, limpet. BIVALVES. 1. Anomia. 2. Pinnu. 3. NIytilus, muscle and motherof-pearl shell. 4. Mya, pearl shell. 5. Spondylus. 6. Chama, clamp-shell. 7. Solen, razor-shell. 8. Ostrea, oyster.t 9. Curdium, cockle. MULTIVALVES. J. Pholas, 2. Chiton. 3. Lepas, bernacle-shell.
IV. VERMES, or worms. Their forms are various and their natures extraordinary, The major part of them are the inhabitants of living animal bodies; their introduction into which is one of those joscrutable mysteries, which must for ever evade the power of human intellect. They exist in most animals; some kinds in the intestines, and sone in the other viscera. The external worms possess an elongated body composed of rings; have circulating vessels, but no beart. No nerves have been discovered in the intestinal worms,
* This animal, known to shell-collectors by the name of the paper-nautilus, is supposed to have given to man the first idea of navigation. When it means to sail, ic discharges a quantity of water from its shell, by which it is rendered lighter than the surrounding medium, and of course rises to the surface. Here it extends two of its arms upward, which are each furnished at their extremity with an oval mems brane, that serves as a sail. The other six arms hang over the sides of the shell, and supply the place either of oars or rudder. It is an inhabit:int of the Mediterranean and Atlantic seas.
opo Oysters breathe by means of gills. They draw the water in at their mouth, a small opening in the upper part of the body, drive it down a long canal, that constitutes the base of the gills, and so out again, retaining the air for the necessary functions of the body.
ORDER I. INTESTINI, or intestinal worms inhabiting the bodies of animals. The genera are: 1. Gordius, guinea-worm. 2. Ascaris, thread-worm, round worm. 3. Tricocephalus. 4. Fasciola, fluke. 5. Tenia, tape worm. 6. Hydatis, hydatid.
ORDER 11. EXTERNI, or external worms. are: 1. Aphrodite, sea-mouse. 2. Sipunculus. 3. Hirudo, leech. 4. Plunariu. 5. Lumbricus, earth-worm. 6. Furia,
Class II.-Insects. 1. Insects are distinguished from other animals by their being furnished with several feet; never fewer than six, and sometimes with many more; by their breathing, not through lungs, but by spiracles or breathing-holes, situated at certain distances along each side of the body; and lastly, by the head being furnished with a pair of antenne, or jointed horns, which are extremely various in the different tribes. The first state in which the generality of insects appear, is that of an egg. From this is hatched the animal' in its second state, in which it is often but improperly called the caterpillar. The insect, in this state, is the larva or larve, being a mask or disguise of the animal in its future form. The larve differs in its appearance, according to the tribe to which it belongs. When the time arrives for the larve to change into its next state of chrysalis, or pupa, it ceases to feed, and having placed itself in some quiet situation, for the purpose, lies still for several hours; and then, by a kind of laborious effort, frequently repeated, divests itself of it's external skin, or larve-coat, and immediately appears in the very different form of a pupa.* The pupa emerges at length the complete insect, in its perfect or ultimate form, from which it never can after change, nor can it receive any further increase of growth. This last or perfect state is termed the imago.
2. Some insects undergo a change of shape, but are hatched from the egg complete, in all their parts, and only
* The Linnæan term pupa was given, from the indistinct resem. blance which many insects bear in this state to a doll, or a child when swathed up, according to the old fashion..
cast their skin from time to time, during their growth, till they acquire the full size of their respective species. The mouth in some tribes is formed for gnawing or breaking the food, and operates by a pair of strong horny jaws, moving laterally, as in the beetle tribe; while in others, it is formed for suction, and consists of a sort of tube. In the butterfly, and moth tribe, it consists of a double tube, which, when at rest, is rolled into a spiral form, and extended at full length when in use. The eyes differ in the different tribes, but by far the greater part of insects are furnished with eyes apparently two in number, and situated on each side the head. The outward surface of the coats of these eyes may be compared to so many convex lenses or glasses. The head of the libellulla, or common dragonAy, is furnished with 25,000 of these diminutive lenses ! In spiders, the eyes are from six to eight in number; of a simple structure, and placed at a considerable distance from each other.
3. The muscles, or organs constituting the several portions of the fesh in insects, are far more numerous than in the larger animals, and are extremely sensible or irritable. In the human body, the muscles scarcely exceed 500, but in a large caterpillar more than 4000 have been discovered! The power of the muscles is also much greater than in animals. A flea is capable of springing at least 200 tiines its own length; whereas the jerboa and kangaroo in their most powerful springs, fall very short of the same proportional distance. Insects are divided into seven orders : coleoptera, hemiptera, lepidoptera, neuroptera, hymenoptera, diptera, and uptera. ORDER I.
COLEOPTERA, or insects which have a hollow horny case, under which the wings are folded, when not in use.
The genera are: 1. Scarubæus, beetles. 2. Lucanus, stag-beetle. 3. Dermestes. 4. Coccinella, Jady-bird. 5. Curculio, weevil. 6. Lampyris, glow
7. Meloe, spanish-fly. S. Staphylinus. 9. Forficula, ear-wig.
ORDER U. HEMIPTERA, or half-winged insects. In this order, the wing-sheaths are tough or leathery at their upper part, and soft or membranaceous at the lower, and the real or under-wings are often of great size, and pleated longitudinally in the manner of a fan. The genera are :
1. Blatta, cock-roach. 2. Gryllus, locust, grasshopper. 3. Fulgora, lantern-fly. 4. (imer, bug, &c.
ORDER 111. LEPIDOPTERA, or scaly-winged insects. The powder or down on the wings of these insects, has been considered as composed of a kind of feuthers; but in reality it is composed of a kind of very minute scales, which differ in size and form in the different species, as well as on different parts of the same species. The genera are: 1. Pupilio, butterfly. 2, 3. Sphin.r and Phalænd, moths.
ORDER IV. NeuroPTERA, or nerve-winged, or fibrewinged insects. This order consists of such as have four large wings, furnished with very conspicuous nerves, fibres, or ramifications dispersed over the whole wing. The genera are: 1. Libellullu, dragon-fiy. 2. Ephemera, mayfly, or trout-fly, &c.
ORDER V. HYMENOPTERA,, or insects having four wings, but not fibrous like the former order. They generally possess a sting or piercer, which in some is innocent; hut in others, it is calculated for the discharge of a highly acrimonious or poisonous juice, as in wasps and bees. The genera are: 1. Vespu, wasp, bornet. 2. Apis, bee. Formicu, ant. 4. Termes, while ant. 5. Ichneumon, &c. ORDER VI.
DIPTERA, consists of insects with two wings only, as the whole race of flies strictly so called, as well as girats, and a great variety of other insects. The genera are: 1. Estrus, gad-fly.* 2. Musca, cominou flies. 3. Culex, gnat, musquito. 4. Hippoboscu, horseleech, &c. ORDER VII.
APTERA, or insects without wings. : Tbe genera are: 1. Podura, spring-tail. 2. Pediculus, louse. 3. Pulex, flea, chigger. 4. dcurus, tick, mite. 5. Araneu, spiders. 6. Scorpio, scorpion. 7. Cancer, crab, lobster, craw-fish, shrimp. 8. Monoculis, water-flea.9. Oniscus, wood-louse. 10. Scolopendru, centipede.
In this genus, the eggs are laid by the parent, in the skin of the backs of cattle, in one species ; in others, in the nostrils and other parts of deer and sheep: the larves, when arrived at eir full size, creep out, and retiring beneath the surface of the grass, or under any convenient body, change into a chrysalis, from which, in a certain space, springs the animal in its ultimate form.
+ The two genera cancer and monoculus are crustaceous, or have a
Class III.-fishes. 1. Like the amphibious animals, their heart is unilocular, or consists but of one chief cavity, and their blood is far Less warm than that of quadrupeds and birds. The organs of breathing in fishes are called gills, and consist of a vast number of blood vessels. The generality of fishes are covered with scales, of various form and size in the different tribes ; which scales are analogous to the hair of quadrupeds, and the feathers of birds. The chief instruments of motion, the fins, consist of a certain number of elastic rays or processes, either of one single piece, in the forin of a spine, or of jointed pieces. The strong or spiny rays are usually placed at the fore part of the fin, and the soft or jointed rays towards the back part. By the various flexures of these organs,
the movements of tishes are conducted; the perpendicular fins, situated on the back or upper part of the animal, keeping the body in equilibrio, while the tuil operates as a rudder at the stern of a vessel, and the side or breast-fius as ours. The stomach is large, and the intestines far shorter than in quadrupeds and birds : the liver is very large, and usually placed on the left side.
2. The air-bladder, or swimming bladder which occurs in the majority of fishes, is a highly curious and important organ. It generally lies close beneath the back-bone, and is provided with a very strong muscular coat, which gives it the power of contracting at the pleasure of the fish, so as to condense the contained gas, or elastic air, with which it is filled, and thus enable the animal to descend to any depth, and again to uscend hy being restored to its largest size. Soine fishes are totally destitute of the air. bladder, and are observed to remain always at the bottom; as the whole tribe of what are termed flat-fish. The teeth are, in some tribes, very large and strong, in others, very hard shelly covering. The crabs and lobsters cast their skins annually, the body shrinking before the change, and enabling them easily to draw out their limbs from the shell. The larger kind of crabs possess the extraordinary power of casting off at pleasure any limb, which may be accidentally maimed or bruised, and a new limb is gradually formed.