The diagram below represents the life cycle of a frog, showing how it became an adult frog.
Overall, there are eight phases of the cycle of an egg becoming an adult frog, each of steps illustrate changes in species body. Phases could be divided into two stage, one is living in the water, second is being adapted to land.
Firstly, frogs mate, generating frogspawn, which later female frog lays. After approximately seven, ten days eggs transform into a tadpoles, tadpoles eat algae to grow further. Later ( six weeks) little legs appear on tadpoles upper body, in nine weeks they envelop further, their upper legs grow more, their lower limbs appears too.
Tadpole reaches next phase in twelve weeks, during these three months tadpoles adapt to land, slowly switching from living in water to land. There froglet phase begins, amphibia starts to breathe pulmonary due to switch of main habitat.
Finally, froglet phase ends and specie becomes a young frog, fully adapted to live on the land and breathe pulmonary. Afterwards young frog will grow, becoming an adult frog.