Unlike chickens, visual cells are evenly distributed in an obvious pattern in many creatures' eyes. The Washington University researchers thought the unusual arrangement in chickens (left) had to do with how the cones are packed into the small, thin layer of eye tissue known as the epithelium. The Princeton researchers developed a computer-simulation model that mimicked the final arrangement of chicken cones (right). The colored dots represent the centers of the chicken's eye cells. They are enlarged and colored for visualization purposes.