Limb regeneration from X-irradiated tails ofAmbystoma mexicanum following transplantation of flank skin from region adjacent to hindlimb.

1. In the experiments performed by W. Luther on youngAmbystoma mexicanum, tails of host animals were irradiated with 2000 r. Afterwards a skin cuff was removed from the mid-tail region. From non-irradiated donor animals, square pieces of skin dorsally adjacent to both hindlimbs were grafted (either 90°-rotated or unrotated) to both sides of the denuded area of the irradiated host tail. After 3 weeks the tails were amputated across the skin transplants, and the structures which had regenerated from the distal portions of the tails were fixed 6-16 weeks later. 2. Morphological and histological investigation revealed that 4 out of 12 regenerates from rotated grafs showed clear limb characteristics. They had developed cartilaginous phalanges and basipodial elements, joint and general connective tissue, and striated muscle fibres. In the remaining eight cases either limb-tailfin structures (four) or amorphous nodes without cartilage (four) had formed. In the two cases with unrotated grafts tailfin-like regenerates had developed. 3. It seems likely that in these experiments the X-irradiated tails represent a passive base on which grafted limb-adjacent flank skin could regenerate limb structures. It follows that the properties of limb regeneration territory can be attributed to these flank skin grafts.