An investigation into the hypothesis of shifting neuronal relationships during development.

The projection of ganglion cells from the centre of the eye to the tectum has been followed during development in Xenopus by an autoradiographic technique. By comparing the caudal limit of this projection with a fixed line of cells labelled with tritiated thymidine the projection has been shown to shift caudally during development. This indicates a less rigid form of neuronal specificity than has previously been accepted.