Tailed Frogs: Ascaphidae

These frogs are found in or near clear, rocky, swift-moving streams that flow through forests. When they are in the fast current, they breathe mainly through their skin and do not have to rely on their lungs as much. Human beings get their oxygen by breathing air into the lungs. There, blood picks up the oxygen out of the air and delivers it through blood vessels to the rest of the body. Frogs can get their oxygen from the water. Water, also known as H₂O, is made up of two chemicals: hydrogen and oxygen. (The H₂ means two atoms of hydrogen are in every molecule of water, and the O means one atom of oxygen is in each molecule.) The water runs past the frog, and blood vessels near the surface of its skin take up the oxygen from the flow. This arrangement allows the frog to survive even though it has very small lungs. On land, the frogs continue to breathe through the skin, which they must keep moist, but they are also able to take up some oxygen from the air through their lungs, as people do.