In the attempts to construct a system, naturalists are commonly said to have followed two methods: the artificial and the natural. The _artificial method_ seizes some one prominent characteristic, and groups all the individuals together which agree in this one respect. In Botany the artificial method classes plants according to the organs of reproduction; but this has been found so very imperfect that it has been abandoned, and the _natural method_ has been substituted, according to which the whole structure of the plant determines its place. If flying were taken as the artificial basis for the grouping of some animals, we should find insects and birds, bats and flying squirrels, grouped together; but the natural method, taking into consideration not one character, but all the essential characters, finds that insects, birds, and bats differ profoundly in their organization: the insect has wings, but its wings are not formed like those of the bird, nor are those of the bird formed like those of the bat. The insect does not breathe by lungs, like the bird and the bat; it has no internal skeleton, like the bird and the bat; and the bird, although it has many points in common with the bat, does not, like it, suckle its young; and thus we may run over the characters of each organization, and find that the three animals belong to widely different groups. It is to Linnæus that we are indebted for the most ingenious and comprehensive of the many schemes invented for the cataloguing of animal forms; and modern attempts at classification are only improvements on the plan he laid down. First we may notice his admirable invention of the double names. It had been the custom to designate plants and animals according to some name common to a large group, to which was added a description more or less characteristic. An idea may be formed of the necessity of a reform, by conceiving what a laborious and uncertain process it would be if our friends spoke to us of having seen a dog in the garden, and on our asking what kind of dog, instead of their saying “a terrier, a bull-terrier, or a skye-terrier,” they were to attempt a description of the dog. Something of this kind was the labour of understanding the nature of an animal from the vague description of it given by naturalists. Linnæus rebaptized the whole animal kingdom upon one intelligible principle. He continued to employ the name common to each group, such as that of _Felis_ for the cats, which became the _generic_ name; and in lieu of the _description_ which was given of each different kind, to indicate that it was a lion, a tiger, a leopard, or a domestic cat, he affixed a _specific_ name: thus the animal bearing the description of a lion became _Felis leo_; the tiger, _Felis tigris_; the leopard, _Felis leopardus_; and our domestic friend, _Felis catus_. These double names, as Vogt remarks, are like the Christian- and sur-names by which we distinguish the various members of one family; and instead of