Order II. Lizards (Lacertilia).—Body with long tail; usually four limbs; scaly; bones of the jaw firm. Examples: striped and green lizards, horned toads, chameleons, iguana.
Order III. Tortoises and Turtles (Chelonia).—Horny and bony shell within which the head and limbs can be drawn; no teeth; eyelids; four legs. Examples: turtles, tortoise, gophers, terrapins.
Order IV. Crocodiles and Alligators (Crocodilia).—Covered with scales and bony plates, teeth in sockets; heart with four cavities; eyelids and earlids. Examples: Crocodile and alligator.
Class IV. Batrachia (Gr., batrachos, a frog), or Amphibia (Gr., amphibios, having a double life).—Animals that can exist for a considerable time on dry land or in water. They are oviparous, hatched by the heat of the sun from eggs, covered with a soft, glutinous membrane, which the mother had laid in the water, and develop through tadpole stages. In the early period of their existence they are fishlike in their structure, breathing by means of gills and a two-chambered heart; in the later stages of their development they acquire lungs and a heart of three chambers. A true amphibian possesses at once both lungs and gills. Examples: frog, toad, newt and salamander.
Class V. Pisces (Lat., piscis, a fish).—Fishes, oviparous animals covered with scales, which form an important part of their special organization for life in the water. Their gills, acting as lungs, extract air from the water instead of from the atmosphere.
Order I. Sharks and Rays (Elasmobranchii).—Shagreen skin; gills fixed and uncovered; cartilaginous skeleton.
Order II. Ganoids (Ganoidei).—Enameled plates or scales; gills free; skeleton partly cartilaginous. Examples: garpikes, mud-fish, lung-fish.
Order III. Bony or Fin Fishes (Teleostei).—Skeleton bony; scales; fins; usually four pairs of gills; mostly oviparous. Examples: bass, perch and ten thousand other kinds.
Class VI. Arthropoda (Gr., arthron, joint; pous, foot).—Metazoa, with definite number of segments; jointed legs; distinct feet and hard, external skeleton.