Aspects of tail muscle ultrastructure and its degeneration in Rana temporaria.

1. Tail muscles of larval Rana temporaria and to a lesser extent Xenopus laevis, at prometamorphosis, were investigated by light and electron microscopy. In the case of Rana their degeneration is described at metamorphic climax. 2. The non-degenerate tail muscles of both genera are generally similar in their ultrastructure and likewise similar to those striated muscles of other adult vertebrates including amphibians. 3. At climax tail muscles of Rana degenerate by autolysis. It seems likely that lysosomal enzymes are directly involved in sarcoplasmic degeneration. The relationship between lysosomes and myofibrillar degradation is difficult to establish. The subject is discussed in the light of relevant information (mainly mammalian) on muscle dystrophies. 4. Anuran tail muscle is highly degraded before its probable phagocytosis by mesenchymal macrophages.