It is as yet but a few years since a system of subordinate analogies not less remarkable began to be speculated upon as within the range of the animal kingdom. Probably it also exists in the vegetable kingdom; but to this point no direct attention has been given; so we are left to infer that such is the case from theoretical considerations only. We are indebted for what we know of these beautiful analogies to three naturalists—Macleay, Vigors, and Swainson, whose labours tempt us to dismiss in a great measure the artificial classifications hitherto used, and make an entirely new conspectus of the animal kingdom, not to speak of the corresponding reform which will be required in our systems of botany also. The Macleay system, as it may be called in honour of its principal author, announces that, whether we take the whole animal kingdom, or any definite division of it, we shall find that we are examining a group of beings which is capable of being arranged along a series of close affinities, _in a circular form_,—that is to say, starting from any one portion of the group, when it is properly arranged, we can proceed from one to another by minute gradations, till at length, having run through the whole, we return to the point whence we set out. All natural groups of animals are, therefore, in the language of Mr. Macleay, _circular_; and the possibility of throwing any supposed group into a circular arrangement is held as a decisive test of its being a real or natural one. It is of course to be understood that each circle is composed of a set of inferior circles: for example, a set of _tribe_ circles composes an _order_; a set of _order_ circles, again, forms a _class_; and so on. Of each group, the component circles are _invariably five in number_: thus, in the animal kingdom, there are five sub-kingdoms,—the vertebrata, annulosa, {239a} radiata, acrita, {239b} mollusca. Take, again, one of these sub-kingdoms, the vertebrata, and we find it composed of five classes,—the mammalia, reptilia, pisces, amphibia, and aves, each of the other sub-kingdoms being similarly divisible. Take the mammalia, and it is in like manner found to be composed of five orders,—the cheirotheria, {239c} feræ, cetacea, glires, ungulata. Even in this numerical uniformity, which goes down to the lowest ramifications of the system, there would be something very remarkable, as arguing a definite and preconceived arrangement; but this is only the least curious part of the Macleay theory.