Growth cones and the formation of central and peripheral neurites by sensory neurones in amphibian embryos.

We have examined the primary growth of neurites by Rohon-Beard sensory neurones in embryos of Xenopus, Rana, and Ambystoma. Using transmission electron microscopy we have confirmed that some central longitudinal neurites first grow directly under the basal lamina which surrounds the spinal cord in Xenopus embryos. Using scanning electron microscopy of dissected embryos we have followed the growth of neurites from the spinal cord to their target tissue, the skin. Comparisons between the three genera are made and detailed observations on growth cones during fasciculation, on the somites and on the basal lamina of the skin are presented. The observations are discussed in relation to possible influences on the course of growth of the developing neurites.