Class Amphibia (Greek for having a double life) technically consists of all tetrapods (four-legged animals) that do not have amniotic eggs. Because the eggs will dry out quickly in the air, these species are tied to the water, at least for reproduction. Most species spend time both on land and in the water, although a few remain in aquatic environments. The larvae of most amphibians, such as the frog, resemble fish, but these larvae undergo metamorphosis and grow four legs before becoming an adult. These adults have air breathing lungs instead of gills, lack a lateral line system, and have external eardrums. Amphibians are also characterized by being soft-skinned. Current examples include frogs, toads, newts, salamanders, and a few rare, legless, burrowing species. Amphibians were the first animals to colonize land, and probably evolved from lobe-finned fish, which have stout bones and fins homologous to the legs of amphibians. Another theory suggests that they evolved from lungfish. Amphibians were much more predominant in the past, but many species became extinct. However, some species gave rise to the reptiles, the first species to live solely on land.