Amphibians are animals familiar to mankind. They are animals whose habitats are changing from water to land in the evolution process of vertebrates. Adult amphibians
can live on land; but their production and the nourishment of their young are still being done in water. Their main features include: their body temperature does not remain constant; they are of ovipara, and their young must live in water. Young amphibians can live on land after metamorphosis. They breathe with their lungs. Their skin exposes to the outside but are very humid. They've no scales. The mucus gland of their hair is rich in secretion and has the function to assist breathing. Amphibians originated in the Devonian period of 300 million years ago. In the long process of evolution, fishes gradually perfect themselves and adapt themselves to live in the new environment on land. Thus, they become amphibians. They are the earliest four-leg animals on land.
