This class includes snakes, lizards, turtles, crocodiles, and tuatara and other extinct species. Among all of the existing reptiles there are 2,500 species of snakes; 2,500 species of lizards; about 250 species of turtles; 22 species of crocodilians, and two species of tuataras. They are distributed throughout the temperate and tropical regions of the world. Since reptiles are cold blooded they can not live in permanently cold places such as the Polar Regions. But there are several species that can be located in the north of the Arctic Circle. The majority of the reptiles are egg laying organisms that are known as oviparous. But many snakes and lizards are viviparous or give birth to living young. The eggs of reptiles have 4 specialized membranes: the amnion, the yolk sac, the allantois, and the chorion. The amnion surrounds the embryo and contains the amniotic fluid. As the embryo develops, the allantois grows out from the embryo hindgut. The yolk-sac membranes cover the yolk, which is used as food for the growing embryo. The chorion surrounds the embryo and the other membranes. In most snakes and some lizard's only one

lung works: in other reptiles, both lungs are equally developed.Reptiles are commonly called cold-blooded. But that is not really true. I say this because some reptiles when they are active have bodies at a higher temperature than most other mammals. The difference is that reptiles rely on external or outer sources of heat. Where as birds and mammals use internal heat. Reptiles regulate their body temperature by getting their heat from the sun, warm stones, warm logs, and the heated earth. Usually the body temperature of the reptile is higher than the surrounding air.A snake is a common word for reptile belonging to the serpent family. The body is elongated and usually cylindrical. Sea snakes and tree-dwelling snakes have the body compressed laterally. Snakes lack external limbs, but some snakes such as boas and pythons are at the base of the tail. The body is covered with scales and a horny epidermal material arranged in rows and over lap each other, sort of like tiles on a roof. The frequency of the shedding of the skin varies from snake to snake. Shedding occurs based on the age and species they are and the size of the individual is. Young rapid growing snakes shed more frequently than slow growing adults did. In some species the skin is shed every 20 days; and in others it is shed only once a year. The venom is a complex mixture of proteins that destroys certain types of tissues. Venom are classified in two major categories: neurotoxic, or nerve affecting, and hemotoxic, or blood affecting. Actually all venom's have elements of both types, but one is more dominant than the other is. The neurotoxic type is more effective, usually acting on the central nervous system. That produces respiratory failure of the heart. Hemotoxins destroy blood cells, the lining of the blood vessels, and other tissue. Because of this the hemotoxic venom spreads more slowly and has a slower action than the neurotoxins. Snakes have well-developed nervous system and they are very smart. They are smarter than some fish and mammals and very adaptable to all conditions. When put in a hostile environment the harmless snakes can seem more dangerous than the venomous snakes. Snakes vision is well developed. They have an acute sense of smell and rely on it heavily when they are hunting. The tongue flicks out, picking up odors that carry to the roof of the mouth into contact with a sensory receptor called the Jacobson's organ. The tongue also receives touch stimuli. Snakes are deaf to airborne sounds. They can perceive vibrations through the ground or whatever they are resting on. The pit vipers as well as some boas and pythons, have another type of sense organ. They have a heat receptor that can perceive small differe

Some common words found in the essay are:
Arctic Circle, America Crocodilians, American Box, REPTILES Reptile, American Crocodile, America River, Galapagos Islands, Cuban Crocodile, Polar Regions, India America, 2500 species, body temperature, length 23 feet, heat sun, 23 feet, mouth closed, families live, 250 species, crocodile found, shell called, nervous system,
Approximate Word count = 1827
Approximate Pages = 7 (250 words per page double spaced)