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Egg
Amphibians begin their lives as eggs, suspended in a jelly-like substance. This jelly coating helps hold water in to ensure the eggs do not dry out. Eggs are laid by the female, often in water or, for some species, on land in a moist environment. The incubation period differs with the species, but during incubation a small embryo appears. You can often see this embryo if you look at amphibian eggs closely.
Tadpole
After the embryo has developed, it breaks free of its jelly-coated egg and enters the world as a tadpole. It has external gills to extract oxygen from the water, and a sucker which it uses to cling to plant matter. This is one of the most vulnerable stages in an amphibian's life cycle because it is nearly defenseless against predators and vulnerable to disease. After a few days, the tadpole begins to feed on algae and a fold grows over its exposed gills.
Metamorphosis
As the tadpole begins to grow, it will begin to come up to the surface to breathe air. It's diet will also adapt, and it will begin to eat small invertebrates living in the water. At this point the tadpole is beginning to undergo the early stages of metamorphosis. Soon small legs will sprout at the base of the tadpole's tail to help propel the tadpole through the water and, later, for use on land. The tail begins to shrink in size and front legs also appear.
Adult
Once the tadpole's tail has almost completely disappeared, and its front and rear legs are fully formed, the tadpole will emerge onto land as an adult amphibian -- such as a frog or newt. Once it has reached sexual maturity, it will reproduce. In order for reproduction to occur, a male adult amphibian must mount a female, allowing him to fertilize the eggs as she lays them. Female amphibians often choose to lay their eggs in water among plant matter, to help camouflage them. They can lay up to 4,000 eggs at one time, starting the life cycle of an amphibian over again.