Extra laminar fibre.
An extra large fiber profile is found in each cartridge of lamina (first order optic lobe); adults exhibit defective phototaxis and optomotor responses (e.g., higher than normal light intensities needed for vigorous responses); light-off transient spike of electroretinogram weak. Morphological difference from normal may no longer exist in adult lamina (Meinertzhagen).
Normal orientation effects in the fixation Y-maze.