Limb regeneration in adult amphibia

This paper reports a histological analysis of limb regeneration capacity in 20 species of amphibians. These data, along with a survey of other species reported in the literature, are used as a basis for the following generalizations. (1) Limb regeneration in the amphibians is not an all-or-none process, but regenerative capacity covers a continuum from normal regeneration to total absence of regenerative ability. (2) In adult anurans, regenerative outgrowth is common in discoglossids and pipids, occurs frequently in hylids, rarely in ranids, and has never been reported in bufonids. In the anurans, there is no correlation between size and regenerative capacity. (3) In the urodeles, limb regeneration capacity is correlated with size. Urodele species with a mean snout–vent length over 100 mm regenerate heteromorphically or not at all. Those under 75 mm regenerate consistently normally. Those species of intermediate size give variable responses to limb amputation, and may regenerate normally, heteromorphically, or not at all. Hypotheses that might explain differences in regenerative ability are discussed.