Supernumerary limb structures with regenerated posterior chick wing bud tissue

When a large wedge of stage 21 posterior chick wing bud tissue was removed and the cut edges were pinned together, wings with a complete complement of skeletal elements developed in 91% of the cases. Twenty‐four hours after removing this wedge of posterior limb bud tissue, tissue had regenerated that was capable of causing the formation of supernumerary (extra) limb skeletal elements when transplanted to a site in the anterior half of a host wing bud. The extra structures formed were similar to those formed when a wedge of non‐regenerated, posterior edge, stage‐21 wing bud was transplanted to a more anterior position in a host wing bud. When a rectangular shaped portion of posterior edge stage‐21 wing buds was removed and the cut edges were not pinned together, five of 15 cases formed a wing with a complete set of skeletal elements and the rest were missing an ulna and/or digit IV or digits III and IV. Twenty‐four hours after removing this rectangle of posterior‐edge wing bud tissue, tissue had regenerated which, when transplanted to a more anterior position in a host wing bud, resulted in the formation of supernumerary skeletal elements. These results are contrary to those obtained by Fallon and Crosby ('75), who concluded that there was no regeneration of posterior wing bud tissue capable of causing the formation of supernumerary wing structures when transplanted to a more anterior position in a host wing bud.