Abstract
Left hindlimbs of toad larvae were amputated at the femur level at five different larval stages. Polydactylia was manifest in high incidence only when the amputation was made at the end of the limb bud stage and digital anomalies in the regeneratively developed limbs were examined. To disclose the morphogenetic mechanism of this phenomenon, histological examinations of early regenerates, especially of their epidermal caps, were made, as well as anatomical observations of skeletons of polydactylous hindlimbs regeneratively developed. The results revealed that the regenerates in the larvae whose limb amputation was made at the end of the limb bud stage frequently had the irregularly thickened epidermal caps and that the shortening and thickening of long skeletal elements of the limb was associated with polydactylism. Metatarsalia and phalanges also showed various anomalies, such as thickening, fusion and/or split. Based on these findings, the mechanism producing the polydactylism was discussed.
