Practice question

Compound eye of insects and crustaceans is composed of repeating visual units called ommatidium, each serving as independent photoreceptive component. Typical ommatidium contains corneal facet acting as lens, crystalline cone focusing light, retinula cells forming rhabdom containing visual pigment rhodopsin, and surrounding pigment cells isolating optical cross-talk. Eight retinula cells often present. Facet denotes external hexagonal cuticular lens; ocellus denotes simple eye; retina denotes vertebrate layer. Ommatidial count correlates with acute motion detection. Structure enables mosaic or superposition imaging, polarization sensitivity and rapid flicker fusion supporting navigation, prey capture and mate finding.