FROG

Whether it's a bright blue poison dart frog or a brown, warty toad, a frog's survival is all about water. Most frogs begin their lives as jelly-like eggs that need moisture to develop. The eggs hatch into aquatic tadpoles, which breathe through gills. As the tadpoles grow, they develop lungs and gain the ability to breathe air.

But frogs' need for water doesn't dry up once they're on land. Frogs get virtually all of their water and part of their oxygen through their skin, and this process only works if their skin stays moist. If a frog's skin dries out, it can't get enough oxygen or get rid of enough carbon dioxide, and it dies

So it should come as no surprise that frogs have developed some interesting adaptations to cope with their lifelong need for water. For example, gastric brooding frogs, which are now extinct, swallowed their eggs. They stopped eating and digesting food while their young