Reptiles include Alligators, Crocodiles, Turtles, Lizards and Snakes. It is commonly said that reptiles are cold-blooded. This means that the temperature of their blood varies and is the same as the surrounding medium. The temperature of an Alligator that has been floating with its nose out of the water is the same as the surrounding water. The temperature of a turtle in the winter time is the same as the mud in which it is buried, while in the summer time it is much higher. What is true of the reptiles in respect to temperature is also true of Amphibians and Fishes. However, this is not true of Birds and Mammals, for these have a uniform temperature so high that they are called warm-blooded. [Illustration: GILA MONSTER So called from the Gila River in Arizona. The only member of the lizard family known to be venomous except the very similar crust-lizard found in Mexico. Range: Desert regions of southern Arizona and New Mexico.] In the United States there is but one species of Alligator and but one species of Crocodile, both limited to the Southeastern States. There are about fifty kinds of Turtle and Tortoises in North America, some of which live on the land and feed largely upon plants, _e. g._, the Common Box Turtle, found from the New England States to South Carolina and westward to Kansas, and the Gopher Tortoise of the Southern States. Others are aquatic, like the Painted Turtles, which are found in one form or another practically all over the United States. Many of these reptiles are highly prized as food, _e. g._, Diamond-backed Terrapin, Soft-shelled Turtle, Snapping Turtle and Gopher Tortoise. [Illustration: COMMON BOX TURTLE Range: Eastern United States] There are about one hundred species of Lizards in North America, the greatest number being found in the drier parts of the continent. Of this whole number only two species are poisonous, and only one of these, the Gila Monster, is found within the United States, being confined in its range to desert regions of Southern Arizona and New Mexico. The Blue-tailed Lizard or Skink, which occurs from Massachusetts to Florida and westward to Central Texas, is commonly believed to be poisonous in the Southern States, where it is called the Red-headed "Scorpion," but this is one of the popular myths still too common among intelligent people. The Glass "Snake" of the Central and Southern States is a peculiar lizard in that it has no legs. That it is able, after being broken to pieces, to collect itself together again and continue to live is another old myth. [Illustration: DIAMOND-BACKED TERRAPIN Range: Salt marshes of the Atlantic Coast and Gulf of Mexico from Massachusetts to Texas.] About a dozen kinds of Horned "Toads" are found in the western portions of the United States. Although toad-like in the shape of their bodies and in some of their habits, they are really lizards.