Or Reptiles, have neither hair, wool, nor feathers, and their bodies are either naked, or covered with scales. Some lay eggs, and some bring forth their young alive. Some have gills, and others lungs, but the latter have only a portion of the blood passing through them; and thus the blood of reptiles is cold, as it is respiration which gives the blood heat. The senses of reptiles are dull, and their movements are either slow or laborious. The following are the four orders into which this class is divided:-- 1. _Chelonian Reptiles._ These animals have four legs. The body is enclosed in an upper buckler, called the carapace, and an under one, called the plastron. They have lungs which are much expanded; but they have no teeth, though they have hard horny jaws. The females lay eggs covered with a hard shell. The principal animals belonging to this division are the tortoises, which live on land or in fresh waters, and the turtles, which inhabit the sea. 2. _The Saurian Reptiles._ These animals have also expanded lungs, and generally four legs, but some have only two. Their bodies are covered with scales, and their mouths filled with teeth. This order includes all the crocodiles and lizards. The crocodiles have broad flat tongues, attached throughout to the jaws, and the lizards have long narrow tongues, which many of them can extend to a great distance from the mouth. 3. _The Ophidian Reptiles_ are the snakes and serpents. The body is covered with scales, but it is destitute of feet. The lungs are generally well developed, only on one side. Serpents are frequently furnished with poison-bags at the base of some of their teeth. 4. _The Batrachian Reptiles_ include the frogs and toads. The body is naked. The greater part of these reptiles undergo a transition from a fish-like tadpole furnished with gills to a four-legged animal with lungs. Others never lose their gills, though they acquire lungs, and of this kind are the siren and the proteus. THE PISCES,