Stages of forelimb regeneration in Ambystoma maculatum.

A series of normal stages describing the regeneration of larval A. maculatum limbs after amputation through the upper arm or wrist is described. Nine discrete stages were recognized, based on external morphological and associated histological features. These stages are Initial Dedifferentiation (ID), Early Bud (EB), Medium Bud (MB), Late Bud (LB), Early Redifferentiation (ER), Notch (N), 2-Fingerbud (2-FB), 3-Fingerbud (3-FB) and 4-Fingerbud (4-FB). Similarities and differences between this and other staging systems for urodele limb regeneration are discussed. The absence of osteoclasts was a striking feature during dedifferentiation of the wrist, in contrast to their presence in large numbers during dedifferentiation of the upper arm.