The structure of the optic nerve ofHydromantes genei,was investigated by confocal laser scanning microscopy and by the Cajal‐De Castro method. This nerve appears to be composed of un‐myelinated fibres, which is a rare case in amphibians. In view of this and the fact that it contains a relatively small number of nervous fibres, the optic nerve ofH. genei,in comparison with other species of Plethodontidae, can be considered a structure with a low level of complication.Key words: Optic nerve structure ‐ Confocal microscopy ‐Morphology ‐ Amphibia ‐ Anatomy.(Received 21 July 1999 – Accepted 30 August 1999)