The Bolwig's organ (BO) cell cluster is abnormal, with several cells often placed anteriorly from the main BO cell cluster in homozygous embryos. Projection of the Bolwig's nerve is abnormal, with only some of the photoreceptor axons fasciculating, projecting towards P1 and growing out towards P2, while other BO axons show random projections. 10% of embryos have photoreceptor axons that project anteriorly and explore areas far remote from the brain. Some of these axons develop enlarged axonal tips. Axons that project normally show defasciculation while in contact with the optic lobe anlagen.