Frogs lay their eggs in water or wet places. The egg begins as a single cell. Several thousand are sometimes laid at once. Gradually, a jellylike covering develops, which protects the egg. The single cell in the egg eventually splits into two. These two split making four cells, and so on. Eventually, there are many cells in the egg. The mass of cells in the egg come to form an embryo. Organs and gills begin to form, and in the mean-time, the embryo lives off its internal yolk.
After 21 days, the embryo leaves its jelly shell, and attaches itself to a weed in the water. This quickly becomes a tadpole, which is a baby frog. The tadpoles grow until they are big enough to break free into the water. This can take from 3 days to 3 weeks, depending on what kind of frog they will become. The tadpole has a long tail, and lives in the water. It is extremely vulnerable, and must rely on its camouflage to protect itself.
After about five weeks, the tadpole begins to change. Over time, the tadpole becomes more and more froglike. Eleven weeks after the egg was laid, a fully developed frog with lungs, legs, and no tail emerges from the water.