During the process of the growth, some vertebrates live both on the land and in the water for certain period of time and these special vertebrates are named Amphibious. Among all the amphibious, frogs and toads can most commonly be seen in our daily life. In their infancy, they're tadpole in the water and use cheek for absorbing oxygen. After the so-called metamorphosis, they'll be ready to live on the dry land and to breathe with their new organ-lung.
　　Amphibious usually have very slippery skin that has neither scales nor cuticle on the surface to lock the internal water; that explains why they most live in the damp places to prevent the vaporizing of their moisture content. Nevertheless, they can produce some mucus to moisturize their skin so that they can still be able to live freely on the land.
　　One can divide amphibious into three major groups, the first: Frogs, including frogs and toads that belong to Order Anura in Class Amphibia. The second is Order Caudata, like salamander. The third group will be Order Apoda that has no extremities and sized like earthworms. Amphibious are the weakest group among all vertebrates.