Classes.
| Body | With vertebræ | Hot Blood | Viviparous | I. | Mammalia. |
| Oviparous | II. | Birds. | |||
| Cold red Blood | With lungs | III. | Amphibia. | ||
| With gills | IV. | Fishes. | |||
| Without vertebræ | Cold white Blood | Having antennæ | V. | Insects. | |
| Having tentacula | VI. | Worms. |
ORDERS OF MAMMALIA.
The first class, or Mammalia, consists of such animals as produce living offspring, and nourish their young ones with milk supplied from their own bodies; and it comprises both the quadrupeds and the cetacea.
This class was divided by Linnæus into seven Orders: viz. primates, bruta, feræ, glires, pecora, belluæ, and cetacea (this order was called Cete by Linnæus) or whales. The characteristics of these were founded, for the most part, on the number and arrangement of the teeth; and on the form and construction of the feet, or of those parts in the seals, manati, and cetacea, which supply the place of feet:
I. Primates.—Having the upper front teeth, generally four in number, wedge-shaped, and parallel; and two teats situated on the breast, as the apes and monkeys.
II. Bruta.—Having no front teeth in either jaw; and the feet armed with strong hoof-like nails, as the elephant.
III. Feræ.—Having in general six front teeth in each jaw; a single canine tooth on each side in both jaws; and the grinders with conic projections, as the dogs and cats.
IV. Glires.—Having in each jaw two long projecting front teeth, which stand close together; and no canine teeth in either jaw, as the rats and mice.
V. Pecora.—Having no front teeth in the upper jaw; six or eight in the lower jaw, situated at a considerable distance from the grinders; and the feet with hoofs, as cattle and sheep.