We shall best understand the wonderfully complex system of analogies developed by that theory, if we start from the part of the kingdom in which they were first traced,—namely, the class aves, or birds. This gives for its five orders,—_incessores_, (perching birds,) _raptores_, (birds of prey,) _natatores_, (swimming birds,) _grallatores_, (waders,) _rasores_, (scrapers.) In these orders our naturalists discerned distinct organic characters, of different degrees of perfectness, the first being the most perfect with regard to the general character of the class, and therefore the best representative of that class; whence it was called the _typical_ order. The second was found to be inferior, or rather to have a less perfect balance of qualities; hence it was designated the _sub-typical_. In this are comprehended the chief noxious and destructive animals of the circle to which it belongs. The other three groups were called aberrant, as exhibiting a much wider departure from the typical standard, although the last of the three is observed to make a certain recovery, and join on to the typical group, so as to complete the circle. The first of the aberrant groups (natatores) is remarkable for making the water the theatre of its existence, and the birds composing it are in general of comparatively large bulk. The second (grallatores) are long-limbed and long-billed, that they may wade and pick up their subsistence in the shallows and marshes in which they chiefly live. The third (rasores) are distinguished by strong feet, for walking or running on the ground, and for scraping in it for their food; also by wings designed to scarcely raise them off the earth and, farther, by a general domesticity of character and usefulness to man. Now the most remarkable circumstance is, that these organic characters, habits, and moral properties, were found to be traceable more or less distinctly in the corresponding portions of every other group, even of those belonging to distant subdivisions of the animal kingdom, as, for instance, the insects. The incessores (typical order of aves) being reduced to its constituent circles or tribes, it was found that these strictly represented the five orders. In the _conirostres_ are the perfections which belong to the incessores as an order, with the conspicuous external feature of a comparatively small notch in their bills; in the _dentirostres_, the notch is strong and toothlike, (hence the name of the tribe) assimilating them to the raptores; the _fissirostres_ come into analogy with the natatores in the slight development of their feet and their great powers of flight; the _tenuirostres_ have the small mouths and long soft bills of the grallatores. Finally, the _scansores_ resemble the rasores in their superior intelligence and docility, and in their having strong limbs and a bill entire at the tip. This parity of qualities becomes clearer when placed in a tabular form:—