Retinotopic Y cell Y17 (from the fly, Phaenicia sericata), with long tangential projections in the medulla (Me), lobula plate (LoP) and lobula (Lo). The cell was stained with lucifer yellow and reconstructed from merged confocal projections; the neuropil background and cell bodies were stained with propidium iodide. Inset: Golgi preparation illustrating the relationship between the outer medulla arbor of Y17 (arrows) and the medullary strata defined by large lamina monopolar cells L1, L2 and L3. An intriguing feature of Y17's three main tangential branches is that each shares the same orientation and direction with respect to the retinotopic map of its respective neuropil, suggesting a possible functional role involving sensitivity to oriented edges. Here, the ends of the branches extend in directions that correspond to downward in the fly's visual field. Scale bar = 20 µm. (See Douglass and Strausfeld, 1998).