In Lake Xochimilco of central Mexico dwells a rare salamander, the axolotl (Ambystoma mexicanum). In the wild, the axolotls do not metamorphose: adults very much resemble their larval counterparts and keep the external gills that ornate their head. Throughout their lives, axolotls have the ability to regrow lost parts of their body, such as a limb munched by a predator. The process may take months, but when it is complete, a regenerated leg is indistinguishable from the original: fully functional and scar-free. While this phenomenon is common in salamanders, it is rare in other vertebrates.