The Cetaceæ,—which the naturalists of antiquity ranked among the fishes, though the females bear their young alive, and are furnished with a mammary apparatus,—chiefly frequent the Northern waters, but some of their species are found in the South Pacific. They represent, it may be assumed, about a one-hundredth part of the Mammalia.
The Birds, by their feather-clad bodies, and by the transformation of their two fore-limbs into wings, form the best-characterised class in the whole animal kingdom. But naturalists can no more agree as to the number of their species than as to the number of species composing the Mammalia. Some, taking as a foundation the rich ornithological collection in the Berlin Museum, allow for 6000 species being distributed over the surface of the globe; others, like Lessen, increase the total to 6266; while Dr Gray, no mean authority, raises it to at least 8000.
The majority of the Raptores, or birds of prey (vulture, falcon, eagle), as well as nearly all the Waders (stork, crane, heron), and Palmipedes (duck, goose, water-hen), are cosmopolitan birds. The other orders, such as the Scansores (parrot, parroquet, magpie), the Passeres (comprising nearly all the singing birds), and the Gallinaceæ (pheasant, pintado), prefer, as a general rule, the warm temperate regions. They are not found in the extreme north, nor in the equatorial climes, except in limited numbers.
Summary of the Mammalia.
Assumed total, 1600 species.
| Bimana | form | 1 | species. |
| Quadrumana | " | 105 (?) | " |
| Carnivora | " | 510 (?) | " |
| Rodentia | " | 508 (?) | " |
| Ruminantia | " | 165 | " |
| Marsupialia | " | 123 | " |
| Edentata | " | 152 | " |
| Pachydermata | " | 38 | " |
| Cetaceæ | " | 18 (?) | " |
| —— | |||
| 1600 |
[Of course, the foregoing is but an approximative estimate, but it will provide the reader with a tolerably accurate notion of the proportion borne by the different classes of Mammalia.]
About 5000 species of birds have been classified. By Cuvier's system they are divided into six orders:—
1. Raptores, or birds of prey.
2. Passerine birds, now generally called Insessores, or Perching-birds.
3. Scansores, or Climbing, frequently called Zygodactyli or Zygodactylous birds.
4. Gallinaceæ, now more frequently known as Rasores.
5. Grallatores, Waders, or Stilt birds.
6. Palmipedes, or Web-footed birds, now more generally recognised as Natatores, or Swimmers.