Histogenesis and distribution of red and white muscle fibres of urodelan larvae.

A histochemical and electron microscopical study has been made of the myotomal musculature of an urodelan (Hynobius tokyoensis) tadpole tail and trunk. In older larvae (stage 64) two main types of fibre (small red and large white) could be distinguished on the basis of differences in fibre size, succinic dehydrogenase and adenosine triphosphatase activities, and fine structural features. The red fibres were superficial to the white ones except at the level of the notochord, where red and white were mixed in mosaic fashion. The superficial and deep red fibres were similar in their histochemical and fine structural characteristics.