Regeneration from half lower arms in the axolotl.

A technique involving grafting of pieces of skin from the head onto the limb in order to isolate halves of the limb is described. This technique was used to isolate posterior, anterior, dorsal and ventral halves of the lower arm. All halves produced regenerates but no part of the limb was able to produce a high proportion of regenerates with a complete pattern of skeletal structures. Posterior half stumps regenerated limbs with a mean digit number of 2.7 and had a normal dorsoventral muscle pattern. Anterior half stumps produced a high proportion of single-digit regenerates and had a mean digit number of 1.3. Dorsal and ventral half stumps regenerated limbs with a mean digit number of 2.8 and 2.3 respectively. Hypomorphic regenerates from dorsal and ventral half stumps often had only dorsal or ventral muscle. These results are in contrast to those from the upper arm (Wigmore & Holder, 1985) where a complete skeletal and muscular pattern regenerated from posterior and dorsal halves and hypomorphic regenerates were obtained from anterior and ventral half limbs.