Eye

Many invertebrate animals have simple light-sensitive eye spots, consisting of a few receptor cells in a cup-shaped A cutaway anatomy of the human eye. Illustration by Hans & Cassidy. Courtesy of Gale Group. organ lined with pigmented cells, which detect only changes in light and dark regimes. Arthropods (insects, spiders, and crabs) have complex compound eyes with thousands of cells which constrict composite pictures of objects. They are very sensitive to detecting movement.