The process in which a tadpole turns into a frog is called metamorphosis, and it is an amazing transformation. Here we have broken metamorphosis down so you can see the stages a tadpole goes through as it develops into an adult. It is important to note that the frogs in the following pictures are not all the same species.
This is an egg mass laid by a frog. Each of those black dots is made up of a bunch of cells that will eventually grow into a tadpole. Depending on the species, these egg masses can be made up of several hundred eggs!
Within a few days, the eggs develop into tadpoles. Tadpoles live completely underwater. After a few weeks, a hormone in the tadpole’s thyroid gland initiates metamorphosis.
Tadpole with hind legs
Over about a 24 hour period, the tadpole develops into a frog. This means almost every organ has to change so the tadpole can go from living underwater to living on land as an adult frog. In this picture you can see the tadpole has started to grow hind legs.
Tadpole with front and hind legs
After the hind legs have started to form, a pair of front legs will begin to develop and the tail will start to disappear. You might also notice that the tadpole has started to form a frog-like face. The tadpole’s skull is made out of cartilage (the same stuff your nose and ears are made out of) but during metamorphosis, the cartilage is replaced with bone.
Froglet (or young frog)
When the tadpole reaches the froglet stage, it is almost a full adult. At this point, the tadpole’s gills have disappeared, and its lungs have enlarged. This means it is ready to leave the water and live on land. Once its tail disappears, it will become an adult frog.
This is a fully grown frog. As you have just read, frogs go through a lot to get to this phase. They even go through changes that aren’t visible in these pictures. The tadpole’s horny teeth, once used to tear up plants, disappear and tongue muscles develop to catch insects. The tadpole’s large intestine, important for digesting algae and plants, shrinks to suit the frog’s meat-eating diet.
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