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
Continuing with developmental changes, "T. carnifex" will undergo a coupling of many processes as it eases into adulthood. Some of these processes include the metabolic needs of different tissues, cardiac activity, and respiratory procedures such as gas exchange. This coupling will be achieved by the autonomous nervous control system. More developmental changes include humoral and nervous control mechanisms, which will actually combine so that response to physiological and environmental changes will be met with a more coordinated reaction. The nervous system assists in development of cardiovascular functions, but this change will occur much later in life. Any time there is a switch from one type of respiration (e.g. cutaneous) to another (e.g. lung) there will be a required alteration and modification of the circulatory system. Another increase that comes with development is that of blood pressure. This is due to both the increase of blood in the organism due to size increasing, and as a response to the enlargement of internal organs.
It has been said earlier that "T. carnifex" is an oxyregulator, and internally can change its physiology to maintain respiration even in oxygen poor environments. However, this is not true for the larval and embryonic stages of "T. carnifex". At these points in development, the "T. carnifex" are oxyconformers. In the earliest stages of embryonic life, cardiovascular activity is not linked or correlated with the activities that produce metabolism changes as in adults. Thus, many changes will have to occur for the organism to reach the mechanisms it contains as a fully developed animal.
The heart (and related structures) is the first organ to operate functionally. This is necessary for many reasons, as the heart is responsible for distribution of everything throughout the body and embryonic development requires a great deal of things to proceed normally. One such reason of its primary operation is the structuring of the vascular system, such as capillary networks found in varying tissues.