Page 79 - Fish and Amphibians (Britannica Illustrated Science Library)

74 AMPHIBIANS FISH AND AMPHIBIANS 75

Axolotl Regeneration Mythology

Another trait of the axolotl is its outstanding
ability to regenerate its extremities and other In Aztec mythology, the axolotl (atl means “water” and xolotl
means “monster”) is the aquatic form of Xólotl, the god for
his plump amphibian is a classic example of neoteny—the ability to reproduce without parts of the body, including parts of its head. It can
regenerate itself through the proliferation of stem which it is named. Xólotl feared death, refused to accept it, and
developing completely into an adult. The axolotl has a flat tail and large external gills, cells in the affected area. These cells multiply and sought to escape it using his powers of transformation. The
T which most salamanders lose when they reach maturity and begin to live on land. The differentiate to replace the missing tissue. legend recounts that, to flee Death, he ran to the water, where
Interestingly, the ability to regenerate is shared by he became the fish called axolotl. This action becomes his final
axolotl is mostly nocturnal and feeds chiefly on invertebrates. It, in turn, can wind up as the other amphibians of the order Urodela. metamorphosis, because Death finally finds him
and kills him.
prey of a water bird. The axolotl was once considered a delicacy, but it is now legally protected.

Neoteny
Lake Latitude
Zumpango One of this animal's notable traits
AXOLOTL 99°
is neoteny—that is, reaching sexual
Ambystoma maturity while in a larval stage, never
mexicanum LAKE
XOCHIMILCO experiencing metamorphosis. Neoteny is
Lake caused by low levels or the complete
is the only place on
Xaltocan absence of thyroxine as the result of a
the planet where
low-functioning thyroid gland. In axolotls,
Habitat Mexico (Lake Xochimilco) the axolotl is found
in the wild. Longitude thyroxine can be generated under
19° 30 experimental conditions by
Habits Mainly aquatic administering iodine.
Length 10-12 inches (25-30 cm)
Tenochtitlán
Life span 25 years
Lake
Texcoco
EXTERNAL
GILLS
are a trait that most
Lake
Lake Chalco salamanders lose when
Weight Xochimilco 12 inches they reach maturity and
1.5 pounds (0.7 kg)
12 inches begin to live on land.
(30 cm) (30 cm)
Life Cycle An adult axolotl can be 10 to
12 inches (25-30 cm) long.
The female lays a large number of eggs. The
time of incubation depends largely on the
temperature. At 60° F (16° C), incubation averages
19 days. At the age of six months, the animals are
COLORS
very active swimmers. They reach sexual maturity Usually they are dark
at one year of age and adult size at between two brown with white spots.
and three years, never losing certain anatomical and In captivity or in their
physiological traits of the larval stage.
natural environment,
some are albinos with
red or gray gills.
SKIN
Unlike salamanders and
other metamorphosed
amphibians, axolotls do
ADULT not shed their skin.
At two or three
years of age
EGGS EXTREMITIES
The extremities are fragile
and delicate. In albinos, the
bones can be seen through
FULL-GROWN
the thin, transparent skin.
Axolotls have four toes on
each front foot and five on
LARVA each hind foot.