Specificity and retinotectal projections of quarter-eye fragments in Xenopus laevis.

Three quarters of the eye anlage in Xenopus embryos of stage 33/34 were eliminated in three different sets of experiments. The remaining quadrant originated from the nasoventral part of the retina, from its ventral portion, or from the temporo-ventral area of the retina. All the fragments developed into small eyes of normal shape. The retinotectal connections did not deviate from those found in the control groups, even though mirror-image duplication was fairly frequent. For all fragments the tectal projection fields were rather limited. There was some indication of fragments retaining their original specificity. Irrespective, however, of their different origins, the optic projections always occupied the rostrolateral area of the tectum.