Constant occurrence of an ipsilateral retino-tectal projection in the axolotl (Ambystoma mexicanum) revealed by horseradish peroxidase tracing.

Cut optic nerves were filled orthogradely with horseradish peroxidase (HRP) to reveal contralateral and ipsilateral retino-tectal projections in the axolotl, by light and electron microscopy. The ipsilateral projection is small but consistently present. It is concentrated in the rostral tectum particularly the dorsomedial and ventrolateral areas. The results are compared with findings in other vertebrates.