Source: Produced for Teachers' Domain
NARRATOR: When some animals grow up, they not only get bigger, their whole body shape changes. Tadpoles are baby frogs that live in the water. Like fish, they breathe oxygen from the water through their gills. After about two years, this bullfrog tadpole is finally ready to change into a frog, in a process called metamorphosis.
First, tiny legs appear near the tail. A front leg grows, elbow first. The small mouth and eyes change. As the eyes move upward and stand out, the frog can see above water (frog croaking). The mouth becomes wider, and the frog can eat insects.
The froglet uses up nutrients stored in its tail. Slowly the tail is absorbed into the body. A strong pair of legs and feet grow, good for jumping on land. The gills disappear and lungs develop, and the frog can breathe air, just like us. Within only ten days, the tadpole has become a frog and is ready to live mainly on land.
Dragonflies are found in ponds, rivers and streams in most parts of the world. Dragonfly babies are called nymphs. Like tadpoles, they live in the water. When they're old enough to change into grownup dragonflies, they climb up out of the water.
This nymph is holding on to a stalk of grass with its feet. The outer skin on its back splits open and the new dragonfly begins to climb out. At first, its wings are soft and crumpled. As blood pumps through the veins, the wings and body get bigger and harden. It takes about five hours before the adult dragonfly is ready to fly and feed. If you look carefully, sometimes you can find the old skins of nymphs still stuck to the grass.
This caterpillar will grow up to be a beautiful monarch butterfly. As a caterpillar, it lives on the milkweed plant, where it eats a leaf a day...which is like a person eating 40 pounds of salad a day.
The caterpillar goes through metamorphosis, too. When it reaches about two inches, or five centimeters long, it attaches to a twig head down. It wriggles out of its skin and forms a hard chrysalis—a kind of caterpillar sleeping bag. Inside, an extraordinary transformation takes place.
After about two weeks, the monarch butterfly breaks out of the see-through chrysalis. Like the dragonfly, it pumps blood through the veins of its wings. In a few hours, with its wings dried and hardened, the monarch takes to the air.
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