Fig. 1. Each branch of the evolutionary tree includes multiple eye types, and their distribution suggests that each type must have evolved several times independently. Single-chambered eyes are outlined in rectangles and compound eyes in ovals. The color of the outline is red for eyes that form images using only shadow, blue for eyes that use refracting devices such as lenses or corneas, and green for eyes that use mirrors. Adapted, with permission, from Land and Nilsson (Land and Nilsson, 2002).