The number of frog sciatic axons increases continually during body growth.

Frog sciatic nerves show a continuing addition of new myelinated and nonmyelinated fibers with body growth. Along with increases in fiber number there are also marked changes in axon calibers and in the relative thickness of the myelin sheaths. Our data show that frog nerves, as opposed to mammalian nerves, are composed of fibers of different ages, stages of growth and stages of myelination.