Fig 1. Schematic representation of the Drosophila visual system.

(A) Schematic representation of Drosophila axonal photoreceptor projections in the third instar larva optic lobe. The outer R1-R6 (indicated in light blue) from each ommatidium in the eye disc project their axons into the lamina part of the brain. At this early developmental stage, the inner photoreceptor R8s (yellow) project through the lamina and establish a regular retinotopic array of terminals in the medulla. (B) Schematic representation of the adult Drosophila visual system. R-cell axons are organized into synaptic-columns and layers. Six different photoreceptors (indicated in light blue) from six neighbouring ommatidia share the same optical axis and pool their axons in the same synaptic-column in the lamina [2]. R8 (orange) and R7 (green) photoreceptor axons pass through the lamina and terminate in distinct synaptic-layers M3 (R8) and M6 (R7).