Right fore-leg buds and right hind-leg buds ofXenopus larvae in the developmental stages 48, 49, and 50 were grafted into an epidermal "pocket" next to the right hind-leg bud (heterotopic) in hosts of the same age. 2. The grafts develop "herkunftsgemäß" to normal fore- and hind limbs. 3. The grafts are also able to develop double limbs. The symmetry of the limbs follows Bateson's rule. 4. In addition to a grafted fore- or hind-leg bud, a supernumerary fore- or hind-leg bud is able to develop. After duplication of the grafts, correspondingly two supernumerary limb buds develop. 5. The supernumerary limbs are orientated as mirror images to the grafts or double limbs and follow also Bateson's rule. 6. The condition for the growth of the supernumerary limb buds is apparently the direct contact of the grafts' plane of amputation to the overlying epidermal "pocket" tissue. In the area of contact the epidermal "pocket" tissue grows and takes part in the formation of the supernumerary limb. 7. In one case, a supernumerary hind-limb exhibits uncoordinated movement. The innervation of this limb is supplied by a branch of the spinal nerve S.
