An amphibian is a vertebrate that lives in water as a larva and on land as an adult, breathes with lungs as an adult, has moist skin that contains mucus glands and lacks scales and claws ( however there are some exceptions for this). They have adapted for living enterily on land. The word amphibian means "double life" , these animals live both in water and on land. The larvae are fishlike aquatic animals that respire using gills. In contrast , the adults of most species of amphibians are terrestrial animals that respire using lungs and skin.
Reproduction in amphibians:
Amphibian eggs dont have shells and tend to dry out if they are not kept moist. In most amphibians the female lays eggs in water and then the male fertilizes them externally, in other species like salamanders, eggs are fertilized internally.
When frogs reproduce the male climbs to the females back and squeezes. The female releases as many as 200 eggs that the male then fertilizes. Frogs eggs are encased and sticky, transparent jelly that attaches the egg mass to underwater plants and makes the eggs difficult for predators to grasp. The embryos are nourished by the jelly until they hatch into larvae that are commonly called tadpoles. tadpoles undergo metamorphosis.
Respiration in amphibians:
In most larval amphibians, gas exchange occurs through the skin as well as the gills. Lungs typically replace gills when an amphibian becomes an adult, although some gas exchange continues through the skin and the lining of the mouth cavity. In many adult amphibians the lungs are reasonably well developed; but some lungless salamanders exchange gases through the thin lining of the mouth cavity as well as through the skin.
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