Fig. 3
From: Exceptional Variation on a Common Theme: The Evolution of Crustacean Compound Eyes
Schematic diagrams of the three basic compound eye optical designs found in crustaceans. a apposition optics; b refracting superposition optics; c reflecting superposition optics. Dashed grey lines represent typical light paths through the crystalline cones to the rhabdoms. cc crystalline cone, R rhabdom, cz clear zone