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

It may be observed with respect to the method followed by Linnæus 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 classes, characterized by various circumstances of their organization. Each of these six classes 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 circumstances. There are thus in his arrangement of animals five gradations: kingdom, class, order, genus, and species. We shall find that the same series is adopted in his classification of the vegetable kingdom. It must be remarked, however, that in nature none[Pg 290] 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 constitute a class. Thus all the individual birds called goldfinches form the species Goldfinch, which with the species Chaffinch and others constitute the genus Finch. This genus, and those known by the names of Grossbeak, Bunting, Lark, &c. constitute the order Passerine 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 classification 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 Linnæan arrangement of animals cannot be considered in any other light; for, if we view it as a natural classification, 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 classifications[Pg 291] 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 classify, 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 classes and orders bear appropriate names, derived from various circumstances. Thus in the class Mammalia, so denominated because the animals composing it bear mammæ and suckle their young, are the orders Primates or Nobles, Bruta, Feræ, &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 Naturæ contains an arrangement of all the species of vegetables known to Linnæus. 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[Pg 292] 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 circumstances, 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. Cæsalpinus, 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 principally 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 passed 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[Pg 293] 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 destitute of flowers. The following is an outline of his system:—