More accurately, amphibians' "double life" refers to two distinct life stages -- a larval stage and an adult stage. Most amphibians lay eggs, which hatch into larvae and undergo an amazing transformation (or metamorphosis) as they move from larval to adult stages. For instance, tadpoles (the larval stage of frogs) have gills and a tail -- features that enable them to live underwater. During metamorphosis, tadpoles lose their gills and develop lungs so they can breathe out of water. At the same time, they begin to grow limbs and lose their tails. The end result: adult frogs who spend much of their time on land.