Most salamanders breed in water and are gregarious at breeding time, when there is usually a courtship display. In most species fertilization is internal. The male deposits sperm packets, which the female picks up with the cloaca; the sperm is then stored until fertilization takes place. The eggs, surrounded by gelatinous material, are usually laid in ponds or brooks, where they develop into aquatic larvae that can breathe by means of gills. A few salamanders breed on land, laying their eggs under rotting vegetation; the young pass through the gilled stage in the egg, emerging as miniature adults. Such strictly terrestrial forms are the red-backed salamander ( Plethodon cinereus ) and slimy salamander ( P. glutinosus ) of E United States and the slender salamander ( Batrachoseps attenuatus ) of the Pacific coast.
Most salamanders, including most that remain in an aquatic environment, go through a typical amphibian metamorphosis into air-breathing adults. Generally the adults have lungs, but in the large family of lungless salamanders (Plethodontidae) breathing occurs entirely through the skin and the lining of the throat. In a few salamanders growth occurs without metamorphosis, and the gilled, juvenile form is able to reproduce. This phenomenon (called neoteny ) is found in the sirens (family Sirenidae) of S United States and N Mexico, in the mud puppies (family Protidae), and in the Mexican axolotl . It may also occur in the Western varieties of the North American tiger salamander ( Ambystoma tigrinum ) under certain environmental conditions. The newts are a large, widely distributed family of salamanders; North American species include the red-spotted newt, which goes through a terrestrial stage known as the red eft.
The North American blind salamanders (several genera in the family Plethodontidae) live in underground streams, caves, and wells in S United States. As adults they have whitish, translucent skin, which covers their eyes. The olm is a European blind salamander related to the mud puppy . The giant salamander ( Dicamptodon ensatus ) of the NW United States grows to 12 in. (30 cm) in length. The hellbender ( Cryptobranchus alleganiensis ) of E United States and the so-called Congo eel ( Amphiuma means ) are large aquatic species. The former, of the same family as the Chinese and Japanese giant salamanders, grows to 20 in. (50 cm); the latter, slender and eellike in appearance, with tiny legs, may reach 30 in. (75 cm).
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