Abstract
Evidence is presented for the existence of two different types of striated muscle fiber from the middle and terminal portions of the tails of the tadpoles Rana catesbeiana, Rana japonica and Xenopus laevis, which were investigated with relation to their histochemical and biochemical properties. The first type of muscle fibers lies immediately below the pigment cells of the skin (peripheral muscle fiber, abbreviated to p.m. fiber); these are of smaller diameter and are abundant in sarcoplasm and mitochondria. The other type (inner muscle fiber, abbreviated to i.m. fiber) lies deeper than to the p.m. fibers; they are of relatively large diameter but contain less sarcoplasm and mitochondria. The intense histochemical localization of lactic dehydrogenase (LDH) activity in the p.m. fibers of the middle and terminal regions of the tail of tadpoles are correlated with the appropriate electrophoretic LDH isozyme patterns. All the zymograms of LDH have been observed to occur faintly at later metamorphic stages.
