Pattern formation following 180° rotation of regeneration blastemas in the axolotl, Ambystoma mexicanum

Forelimbs of larval axolotls were amputated through the distal one‐third of the humerus. The resulting palette stage regeneration blastemas were rotated 180° and replaced on the original limb stump. This surgery offset both the anteroposterior and dorsoventral axes of graft and stump. Supernumerary limbs formed at anterior and posterior regions in the graft–host junction. Most supernumerary limbs displayed variable degrees of fusion with the graft. In these fused limbs the half of the supernumeray limb that was adjacent to the graft developed with the palm dorsally (in harmony with the graft), whereas the half of the supernumerary limb that was adjacent to the stump developed with the palm ventrally (in harmony with the stump). Anterior supernumerary limbs that were clearly separated from the graft were of stump handedness. Posterior supernumerary limbs that were clearly separated from the graft were of handedness opposite to the stump. Two types of derotation phenomena are described. These results are discussed in view of several recent theories for pattern regulation in epimorphic fields.