Newt
During the subsequent few months, the larvae undergo metamorphosis, during which they develop legs, and the gills are absorbed and replaced by air-breathing lungs. Some species, such as the North American newts, also become more brightly coloured during this phase. Once fully metamorphosised, they leave the water and live a terrestrial life, when they are known as "efts". Only when the eft reaches adulthood will the North American species return to live in water, rarely venturing back onto the land. Conversely, most European species live their adult lives on land and only visit water to breed.
Italian crested newt
The gills have their origins in gill arches 2, 3, and 5; these increase with 3 more bars, that consist of secondary filaments, which create the respiratory organ. In the secondary lamellae there are connective tissues that provide support to the epithelium; these make up the water-blood barrier, in particular where the capillaries are immediately below the basal cells. There are numerous secondary filaments along with the main filaments, which are lengthened to extend the oxygen-catching capability. This increase in surface area counteracts the decreased oxygen available, by allowing greater oxygen uptake. In larval stages, the gills are well-developed with a great number of respiratory lamellae. This adaptation is hypothesized to be an advantage in response to the conditions in an aquatic environment.