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  title of the text on amphibians  
         
 

Frogs in a garden      
Did you know that amphibians were the first animals to become terrestrial and live on land? Well, it is so.

Almost all amphibians have two live cycles: they begin their life in (fresh) water and then finish it mainly on land. This is the origin of the word amphibian, which means “both sides of life”. As young amphibians evolve first in water, adult amphibians have to lay their eggs in lakes and rivers; only a few amphibians can survive in seawater (though not thrive), but they are no true marine amphibians. Their eggs hatch into an aquatic larva (tadpole) that resembles a fish with tail and likewise breathes with gills. Then the tadpole goes through metamorphosis and the tadpole grows into its adult air-breathing form with lungs and legs and moves to live on land. Depending on the structure of their body, amphibians will jump, climb or crawl; they dive and swim when in the water.

Adult amphibians have a thin smooth skin that is moist. They breathe with lungs and are cold-blooded animals, which means that the temperature of their body depends on the temperature of the environment they live in. Like reptiles, amphibians have a three-chambered heart - two atria and one ventricle – and a mixture of oxygenated and deoxygenated blood goes through their blood stream.

Common amphibians include frogs, toads and salamanders and also a limbless species that resembles a snake.

 
   
 
A frog's life

A frog’s life begins with a tinny black egg that hatches into a larva (tadpole), so frogs spend their “childhood” in water. The tadpole breathes with gills and has a tail that is very useful for the frog to move. External gills appear first, shortly replaced by internal gills; then legs grow, the tail disappears, and the head and the body grow, too.

life cycle of the frog

Tadpoles breathe in the water because (just like fish) they have gills and can absorb the necessary nutrients. After three months, their gills are replaced with lungs, and the adult frogs breathe through their lungs and their skin, and can move onto land.

Frogs exist in an amazing array of colours and sizes, and are found in nearly every environment around the world (except on the Antarctic continent) from tropical forests to the tundra and the deserts.

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    All Texts and Illustrations © Dulce Rodrigues, 2009. All rights reserved