A phenomenon among some salamanders, in which larvae of large size, while still retaining the gills and other larval features, become sexually mature, mate, and produce fertile eggs. In certain lakes of Mexico, only the neotenous larvae are present and are called axolotls. Neoteny occurs in certain species of the family Ambystomidae, especially in Ambystoma tigrinum of some localities, and commonly in the large Dicamptodon ensatus of the Pacific Coast. It also occurs in some Texas and Oklahoma species of Eurycea. Neotenous larvae of A. tigrinum can be made to metamorphose to adult form if treated with thyroid extract.