Bolwig's organ and the developing projection of eyelet. A, Frontal 8 μm wax section of anterior region of third instar larva showing immunoreactivity to Rhodopsin 6 in Bolwig's organ (BO), situated dorsally to the cephalopharyngeal skeleton (arrowheads). Differential interference contrast microscopy was used.B, C, Horizontal cryostat sections 10 μm thick of pupal optic lobe immunolabeled with antibody 24B10.B, Pupa at approximately P + 45%. In early pupal stages the developing medulla (Me) lies orthogonal to the lamina (La), and the photoreceptor terminals of eyelet are not seen. C, Pupa at approximately P + 70%. At approximately P + 50% the medulla rotates, becoming concentric with the lamina, and the terminals of eyelet immunolabel at a position anterior to the medulla neuropil (arrow) corresponding to the accessory medulla. R, Retina. Cell bodies are not easily seen in this preparation. In the late pupa and adult the axons from the cells of eyelet project through the outer chiasm, and their terminals in the accessory medulla all label with photoreceptor-specific antibodies. Scale bars: A, 10 μm; (in B) B, C, 50 μm.