The nictitating membrane on an albino Red Eye Tree Frog. The Red-Eyed Tree Frog has a third eye lid called the nictitating membrane. This membrane allows them to shield their eyes from danger while still being able to see. This is useful when in a mating battle or when being hunted. The coloring of their eyes also plays a large part in their survival. The bright red causes their predators to second-guess the prey and stuns them to give the Red-Eyed Tree Frog a chance to escape. The red color also allows them to see at night which is useful since they are nocturnal amphibians.
(via The Soul is Bone)