III. THORACICI, _Thoracic_. Fishes having the ventral fins placed under the pectoral; as the goby, bull-head, holibut, gilt-head, perch, mackerel, &c.

IV. ABDOMINALES, _Abdominal_. Fishes having the ventral fins placed on the abdomen behind the pectoral fins; as in the salmon, trout, pike, mullet, and herring.

In this cla.s.s there are 47 genera, and 400 species. The specific characters are taken from the number of rays in the fins, the form of the tail, the cirri or filaments at the mouth, the colouring of the body, the form of the scales, and other circ.u.mstances.

The fifth cla.s.s, that in which the INSECTS are included, comprehends 86 genera, disposed into seven orders, which are founded on the number and texture of the wings.

I. COLEOPTERA, or Hard-winged Insects. Insects having the wings covered by two crustaceous cases. This order is the most extensive, including 30 genera, and 893 species. It includes all the insects commonly known by the name of beetles.

II. HEMIPTERA, or _Half-winged Insects_, having the sh.e.l.ls or cases semicrustaceous, not divided by a straight line as in the coleoptera, but overlapping each other at the margin; the beak curved inwards; 12 genera, 353 species. The c.o.c.kroach, cricket, locust, and cochineal-insect, are examples.

III. LEPIDOPTERA, or _Scaly-winged Insects_, having four wings, which are covered with imbricated scales; the tongue spiral and coiled up, the body hairy. In this order there are only 3 genera, _Papilio_, _Sphinx_, and _Phalaena_, the b.u.t.terflies and moths; but the species are 780.

IV. NEUROPTERA, or _Net-winged Insects_, with four naked, transparent, or reticulated wings; the tail generally dest.i.tute of a sting. There are 7 genera, and 83 species, among which are the dragon-fly, the may-fly, and the scorpion-fly.

V. HYMENOPTERA, or _Thin-winged Insects_, with four naked membranous wings; some species, however, being wingless. The females have the tail armed with a sting. This order contains 10 genera, and 313 species, of which may be mentioned as examples, the wasp, bee, ichneumon-fly, and ant.

VI. DIPTERA, or _Two-winged Insects_, having only two wings, and being furnished with a balance or club behind each wing.

There are 10 genera, and 262 species, among which are the common house-fly, the flesh-fly, and the gnat.

VII. APTERA, _Wingless_. Insects dest.i.tute of wings in both s.e.xes. They are arranged under 14 genera, and consist of 300 species. In this order there are three divisions: some have six feet, as the flea, the louse, and the white ant; others have from 8 to 14 feet, as the spider, scorpion, crab, and lobster; while others have a still greater number, as the centipede.

The generic characters are derived from the antennae, the jaws, the head, the thorax, the wings, the elytra or wing-covers; and the specific, from the colours and other circ.u.mstances. The number of species is 2984.

The sixth cla.s.s, that of VERMES or WORMS, is a very heterogeneous one, and to later authors has supplied materials for several cla.s.ses. Linnaeus divides it into five orders:

I. INTESTINA, _Intestinal Animals_: simple, naked, and dest.i.tute of limbs: for example, the earth-worm, the guinea-worm, the leech, and the ascaris: 7 genera, 24 species.

II. MOLLUSCA. Simple, naked animals, furnished with limbs: the slug, the sea-mouse, the sea-anemone, the cuttlefish, the sea-nettle, the star-fish, and the sea-urchin: 18 genera, 110 species.

III. TESTACEA, _Sh.e.l.l-fish_. Soft, simple animals, covered with a sh.e.l.l which is usually calcareous. This order includes 36 genera, and 814 species. It is divided into three groups, the multivalve sh.e.l.ls, or those which consist of several pieces; the bivalve, of two pieces; and the univalve, or those of one piece only.

IV. LITHOPHYTA. Compound animals, affixed to, and fabricating a fixed calcareous base, called coral. There are 59 species, which are referred to 4 genera, the tubipores, madrepores, millepores, and cellepores.

V. ZOOPHYTA. Compound animals, sending forth processes resembling flowers, and springing from a vegetating stem.

This order contains 15 genera, among which are the red coral, the sea-fan, the sponge, coralline, &c. The number of species is 156.

The characters of the genera and species of these orders are derived from so many various circ.u.mstances, that it would be tedious to recapitulate them. The number of objects defined in this part of the Systema Naturae, is as follows:--

Mammalia, 219 Birds, 930 Amphibia, 292 Fishes, 400 Insects, 2984 Vermes, 1163 Species from the Appendices, 140

In all, 6128 species of animals.

It may be observed with respect to the method followed by Linnaeus in his arrangements, that he has generally chosen the most simple and perspicuous that he could devise. The whole creation he disposes into three _kingdoms_, the animal, the vegetable, and the mineral. The animal kingdom is divided into six great _cla.s.ses_, characterized by various circ.u.mstances of their organization. Each of these six cla.s.ses is divided into several _orders_ and numerous _genera_; and the genera are composed of _species_. Sometimes the species exhibits _varieties_, or variations of form, colour, and other qualities, dependent upon climate, food, domestication, and other circ.u.mstances. There are thus in his arrangement of animals five gradations: kingdom, cla.s.s, order, genus, and species. We shall find that the same series is adopted in his cla.s.sification of the vegetable kingdom. It must be remarked, however, that in nature none of these gradations actually exist. Individuals alone form the subjects of observation; but a number of individuals closely resembling each other are considered in the mind as forming a species; and several species agreeing in certain respects with each other form a genus; while genera united by particular characters compose an order; and the orders const.i.tute a cla.s.s. Thus all the individual birds called goldfinches form the species _Goldfinch_, which with the species _Chaffinch_ and others const.i.tute the genus _Finch_. This genus, and those known by the names of _Grossbeak_, _Bunting_, _Lark_, &c.

const.i.tute the order _Pa.s.serine Birds_. Natural objects may thus be arranged in a definite series, so that the place of any given species may be determined; hence, if the student should be desirous of finding the name and history of a particular object, he can readily discover it, or he can satisfy himself that it has not yet been described. At the same time, it must be remembered, that the cla.s.sification in question is entirely artificial, and does not necessarily place together genera that are the most closely allied. It is a kind of systematic index to the works of nature, and is useful in many respects, although it may not lead to the disclosure of all the peculiarities or all the affinities and relations of the object to be examined. The Linnaean arrangement of animals cannot be considered in any other light; for, if we view it as a natural cla.s.sification, we meet with false positions and erroneous views at almost every step. His disciples mistook it for a perfect system, and viewed the various species with reference to it, rather than with respect to their mutual relations. Still, they who look upon the artificial cla.s.sifications of our great master as having done more harm than good, judge erroneously; for although they are certainly imperfect, without them or others of a similar kind it would have been impossible to retain any distinct remembrance of the numerous objects which have successively been introduced to notice. It were more reasonable to admire the ingenuity displayed in the construction of so simple a system, than to blame the unsuccessful attempt to cla.s.sify, according to their essential peculiarities, objects whose multiplied relations have, to the present day, defied the most accomplished naturalists.

With respect to the nomenclature, it is sufficient to remark, that the cla.s.ses and orders bear appropriate names, derived from various circ.u.mstances. Thus in the cla.s.s _Mammalia_, so denominated because the animals composing it bear mammae and suckle their young, are the orders _Primates_ or n.o.bles, _Bruta_, _Ferae_, &c. The generic names are always substantives, as _Phoca_, _Canis_, _Lepus_, &c.; and the specific names are either adjectives, as _Phoca barbata_, _Canis familiaris_, _Lepus timidus_, or, in certain rarer cases, substantives, as _Canis Lupus_, _Ursus Arctos_, &c. We now proceed to the examination of another kingdom.

The second volume of the Systema Naturae contains an arrangement of all the species of vegetables known to Linnaeus. It is in this department that our author has been generally allowed to excel, and his system, after undergoing some modifications, remains in use at the present day; nor is it likely ever to be superseded by any other merely artificial arrangement.

Before proceeding to a general account of this celebrated scheme, it may be useful to take a brief view of those by which it was preceded. It is obvious, that without a methodical disposition of plants, and a fixed nomenclature, it would be impossible for an individual to retain the knowledge of the numerous and diversified forms which these present.

Descriptions, moreover, would be unintelligible, and we should find it difficult or impracticable to ascertain the species of which authors might write.

The alphabetical arrangement of plants, the most artificial, or at least the most unnatural of all, was at one time much followed by botanists, especially in local catalogues. The time of flowering, the place of growth, the general habit or appearance, and various other circ.u.mstances, formed a basis to other arrangements. In the sixteenth century, Conrad Gesner showed that the flower and fruit were the only parts capable of affording determinate characters. Caesalpinus, physician to Pope Clement VIII., presented the first model of a botanical system, in his _Libri de Plantis_, published in 1583. The characters are derived princ.i.p.ally from the fruit, though likewise from the flowers, and the duration of plants. The two Bauhins, Ray, and Morison, published systems constructed on similar principles. Others, as Rivinus and Ludwig, derived their characters from the corolla. All these methods, however, successively pa.s.sed into neglect, and were superseded by that of Tournefort, who was professor of botany at the Garden of Plants in Paris, in the reign of Louis XIV. This eminent writer was the first who defined the species and genera with any degree of precision. He arranged plants according to the various forms of the corolla, dividing them primarily, according to the consistence of the stem, into _Herbs_ and _Trees_. The former were subdivided into three orders; those with simple flowers, those with compound flowers, and those dest.i.tute of flowers.

The following is an outline of his system:--

_Division I._ HERBS.

* _With simple flowers._

Corolla of one piece, regular.

Cla.s.s I. CAMPANIFORMES, with a regular corolla, of one piece, and resembling a bell; as the convolvulus.

II. INFUNDIBULIFORMES, with a regular corolla, of one piece, and resembling a funnel; as the tobacco.

Corolla of one piece, irregular.

III. PERSONATae, with an irregular corolla, of one piece, resembling an antique mask; as the foxglove.

IV. l.a.b.i.aTae, with an irregular corolla, of one piece, divided into two lips; as the sage.

Corolla of several pieces, regular.

V. CRUCIFORMES, with a regular corolla, composed of four petals, placed crosswise; as the wallflower.

VI. ROSACEae, with a regular corolla, composed of several petals, arranged in the form of a rose; as the wild rose and apple.

VII. UMBELLIFERae, with a regular corolla, composed of five petals, the flowers arranged on stalks resembling the spokes of an umbrella; as in the carrot.

VIII. CARYOPHYLLEae, with a regular corolla, composed of five petals, having long claws; as the pink.

IX. LILIACEae, with a regular corolla, composed of six or three petals, or sometimes of one piece with six divisions; as the tulip.

Corolla of several pieces, irregular.

X. PAPILIONACEae, with an irregular corolla, composed of five petals; as the pea.

XI. ANOMALae, with an irregular corolla, composed of five petals, but differing from the papilionaceous form; as the violet.

* * _With compound flowers._

XII. FLOSCULOSae, with flowers composed of small funnel-shaped, regular corollas, divided into five segments; as the thistle.

XIII. SEMIFLOSCULOSae, with flowers composed of small irregular corollas, of an elongated flat shape; as the dandelion.