Metamorphosis
is generally understood as a typical component of amphibian development.
For most urodeles and anurans, it is the transformation from an aquatic
larva to a terrestrial adult via morphological changes in the body.
There are, however, a number of species that do not follow this basic pattern
of amphibian life. The African clawed frog, Xenopus, is well
known for being a fully aquatic genus. Among a few other urodeles,
the axolotl is also representative of this aquatic lifestyle (Rosenkilde
and Ussing 1996).
In most
of the literature pertaining to axolotl development, the term "metamorphosis"
is used to describe the termination of the aquatic larval period for non-neotenic
urodeles. This is a time characterized by the resorption of the external
gills and tail fin, a change in head morphology, and a thickening of the
skin (Brown 1997). Prior to these morphological changes, however,
the axolotl undergoes major developments such as limb and lung formation,
a changeover from larval to adult erythrocytes, and sexual maturation (Rosenkilde
and Ussing 1995). It should therefore be noted, that while the axolotl
does experience some metamorphosis, common use of the term usually refers
to the complete transformation of the animal in a way that suits a terrestrial
lifestyle (Rosenkilde and Ussing 1996).
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