Linnæus divided this class into six Orders: 1. _Land Birds._ I. RAPACIOUS BIRDS (_Accipitres_).--Having the upper mandible hooked, and an angular projection on each side near the point, as the eagles, hawks, and owls. II. PIES (_Picæ_).--Having their bills sharp at the edge, somewhat compressed at the sides, and convex on the top, as the crow. III. PASSERINE BIRDS (_Passeres_).--Having the bill conical and pointed, and the nostrils oval, open, and naked, as the sparrow and linnet. IV. GALLINACEOUS BIRDS (_Gallinæ_).--Having the upper mandible arched, and covering the lower one at the edge, and the nostrils arched over with a cartilaginous membrane, as the common poultry. 2. _Water Birds._ V. WADERS (_Grallæ_).--Having a roundish bill, a fleshy tongue, and the legs naked above the knees, as the herons, plovers, and snipes. VI. SWIMMERS (_Anseres_).--Having their bills broad at the top, and covered with a soft skin, and the feet webbed, as ducks and geese. ORDERS OF AMPHIBIA. Under the third class, or Amphibia, Linnæus arranged such animals as have a cold, and, generally, naked body, a lurid colour, and nauseous smell. They respire chiefly by lungs, but they have the power of suspending respiration for a long time. They are extremely tenacious of life, and can repair certain parts of their bodies which have been lost. They are also able to endure hunger, sometimes even for months, without injury. The bodies of some of them, as the turtles and tortoises, are protected by a hard and horny shield or covering; those of others are clad with scales, as the serpents, and some of the lizards; whilst others, as the frogs, toads, and most of the water-lizards, are entirely naked, or have their skin covered with warts. Many of the species shed their skins at certain times of the year. Several of them are furnished with a poison, which they eject into wounds that are made by their teeth. They chiefly live in retired, watery, and marshy places; and, for the most part, feed on other animals, though some of them eat water-plants, and many feed on garbage and filth. None of these species chew their food; they swallow it whole, and digest it very slowly. The offspring of all these animals are produced from eggs, which, after they have been deposited by the parent animals in a proper place, are hatched by the heat of the sun. The eggs of some of the species are covered with a shell; those of others have a soft and tough skin or covering, not much unlike wet parchment; and the eggs of several are perfectly gelatinous. In those few that produce their offspring alive, as the vipers and some other serpents, the eggs are regularly formed, but are hatched within the bodies of the females. This class Linnæus divided into three Orders: I. REPTILES.--Having four legs, and walking with a crawling pace, as the tortoises, toads, and lizards.