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 skin of "T. carnifex" is a highly permeable structure, because it is the source of osmoregulation. Due to their skins' ability to absorb water, these newts do not need to drink. "T. carnifex"’s epidermis is divided into three separate cell layers: the stratum corneum, the outer layer, which consists of keratinized cells, the stratum intermedium, the middle layer, which consists of polyhedral cells, and the stratum germinativum, the basal side layer, which consists of a single row of cells. The first layer of cells contains three adaptive characteristics that help protect the epidermal layers. The inner portion of the integument consists of the connective tissue that makes up the dermis layers. This includes the stratum spongiosum, which is made up of loose tissue containing collagen, elastic fibers, blood vessels, glanular and muscous glands, and the stratum compactum, which consists of dense collegen fibers in bundles lying on the inside. The stratum spongiosum is closer to the surface. Altogether, this layer measures 5 micrometers. The thickness and resistance of this layer, combined with the filamentous network of keratin, interfilamentous intermatrix, and the intercellular substance produced by the kerinocytes all help to reduce chemical and physical damage to the underlying tissues and all help to keep a constant internal environment. However, water is still able to get through the layers of the epidermis. Keratinocytes are especially important to the newt’s physiological well-being because they are responsible for the absorption of sodium ions. When it comes time to shed the skin, these cells will thicken and flatten out and eventually become the skin the newt sheds. Since highly permeable skin is a favourable adaption this is the main source of osmoregulation in crested newts.