Linnaeus's Classification of the Animal Kingdom--Remarks on the Gradations employed, and on Nomenclature--Classification of the Animal Kingdom--General Remarks--Method of Tournefort--Method of Linnaeus--Classification of the Vegetable Kingdom--Theory of the Formation of Minerals and Rocks. The work just mentioned bears the title of Systema Naturae per Regna tria Naturae, secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis,--A System of Nature, in which are arranged the objects constituting the three kingdoms of nature, in classes, orders, genera, and species, with their characters, differences, synonymes, and places of occurrence. The first volume contains the animal kingdom. The introduction presents a brief view of the constitution of the world, in the usually laconic style of the author. In it the three kingdoms of nature are thus defined:--_Minerals_ are concrete bodies, possessing neither life nor sensibility; _vegetables_ are organized bodies, possessed of life, but without sensibility; _animals_ are organized bodies, possessing life and sensibility, together with voluntary motion. Objections may be made to these definitions; but it is not our object at present to criticise his views and arrangements, our intention being simply to offer a brief account of them, omitting all that is not absolutely essential. It ought to be understood, that the entire work is merely an index or catalogue of the productions of nature; that it was obviously intended as such by its author; and that they who object to the Systema Naturae, because it contains nothing more than characteristic notes methodically arranged, forget that Linnaeus never professed to give descriptions in it. The natural division of animals, he says, is indicated by their internal structure. This principle his modern adversaries have chosen to overlook, asserting that his classification is founded on external form. In some species the heart has two distinct cavities, and the blood is warm and red; of these some are viviparous,--the _mammalia_,--others oviparous,--the class of _birds_. In certain species the heart has only a single cavity, with a single auricle, the blood red but cold; of these the _amphibia_ have a voluntary respiration, while _fishes_ respire by gills. In other animals the heart has also a single cavity, but without an auricle, while the blood is cold and of a white colour; of these the _insects_ are characterized by their antennae, the _vermes_ or _worms_ by their tentacula. The _Mammalia_, which constitute the first class, are the only animals furnished with teats. Their clothing, hoofs, claws, horns, teeth, and other organs, are briefly described, in such a manner as to enable the student to comprehend the meaning of the terms to be subsequently employed. The characters of the orders are derived principally from the teeth.