With the moist skin of amphibians, oxygen can be taken up through the skin so cutaneous arteries in addition to pulmonary arteries help to oxygenate blood. The now-oxygenated blood drains back into the left atrium , to be pumped by the ventricle to systemic arteries to the body and carotid arteries to the head. Amphibians in water share the same osmoregulatory concerns as do freshwater fish, and so there excrete a lot of dilute urine. Amphibian skin lacks scales, etc., but does have many glands and epidermal thickenings. The specialized coloring seen in many amphibians is the result of chromatophores .
Courtship usually includes sound production, via a larynx and vocal sacs.
The female usually lays eggs in moist areas or water, as the clasping male fertilizes them externally during amplexus . The egg does not have a protective shell. An aquatic tadpole with a tail and gills swims until thyroid hormone control leads to metamorphosis into an adult. Given their dependence on moist habitats for their skin and their reproduction, it is not surprising that amphibians are not currently dominant land organisms. In contrast to the amphibians, the reptiles are able to live away from water.