Skeletal regeneration in amphibians.

T H E failure of de novo regeneration of extirpated bones in adult urodeles has been described repeatedly. Wendelstadt (1901) reported the absence of skeletal regeneration following the removal of either the ulna or radius from the otherwise intact limbs of salamanders. Reed (1903) and Morrill (1918) likewise failed to obtain regeneration of previously excised fibulae in salamander hind limbs. Similar negative results were reported by Schaxel & Bohmel (1928) and Bohmel (1929) following the removal of femurs from axolotls. Gebauer (1933) recorded no regeneration of extirpated bones in Triton cristatus, and Goss (1956) and Rieck & Rudich (1956) noted that ulnae were not replaced after their removal from the limbs of adult Triturus viridescens. In contrast to the situation in adults, Swett & Parsons (1929) have reported the regeneration of completely removed humeri and shoulder girdles in the young larvae of Amblystoma punctatum. In the present research, the problem of skeletal regeneration has been reinvestigated, both extensively and intensively. Firstly, the responses of larval urodeles and anurans to skeletal extirpation has been compared with those of adult urodeles. Secondly, on the theory that the absence of bone regeneration in adults might be due to the more highly differentiated condition of their tissues, as illustrated, for example, by the presence of ossified rather than cartilaginous parts, the replacement of skeletal elements removed from adult limb regenerates of various ages has been analysed. Finally, the possibility that nerves might influence skeletal restitution, as they do limb regeneration, has been investigated.