Reorganization of retinotectal projection of compound eyes after various tectal lesions in Xenopus

The retinotectal connexions of double nasal (NN), double temporal (TT) and double ventral (VV) eyes in juvenile Xenopus were mapped after post-metamorphic removal of the rostral, caudal, medial or lateral tectal halves with the subsequent cutting of the optic nerve of the operated eye. A whole visual field projection occurred from NN eyes on to residual caudal tectum, from TT eyes on to residual rostral tectum and from VV eyes on to residual medial tectum. When optic fibres from NN, TT or VV eyes grew into inappropriate rostral, caudal or lateral tectal halves respectively, there was a projection deficit in the nasal and temporal or in the dorsal and ventral poles of the visual field. The persisting scotomas in the visual field indicated that only the optic fibres of the central retinal fundus had succeeded in connecting with an inappropriate tectal half whereas the peripheral optic fibres had not. The incongruous results of optic nerve regeneration obtained in the various recombinations may be taken to indicate that the assumption of early embryonic pattern regulation is inadequate to explain the findings in this experimental situation.