Arliegh Ham, age l3, of Boise, Ida.., for his question:

How do human and cat eyes differ?

We are told that the cat can see in the dark, but this is not quite true. The cat can see better than we can in a dim lights but it cannot outdo us in total darkness. No cat, or any other animal, can see when there is no glimmer to light the blackness of midnight.

The shiny, bright eyes of a cat are slanted. Even when they are wide open and round, the outside corners tip upward. Their color is very noticeable because the large irises spread to the outside edges of the eyes. In human eyes the colored irises are centered in circles of white cornea. No white cornea shows in the eyes of a cat.

The main difference between cat and human eyes is in the pupils. Human pupils are round, black peepholes in the very center of the irises. The cat has long pupils that can change from narrow to wider slits or become round, black circles big enough to hide most of the eye color. Pupils are windows that let in rays of light carrying pictures of the scenery. They are controlled by muscles that regulate the amount of light that falls upon the retina screens in the back of the eyeballs.

Human pupils are ringed by circular muscles that contract when the light is too bright for the sensitive retinas. This pauses the pupils to shrink to small, round holes. ?Nthen the light is dim the muscles relax, and the pupils grow larger to let in as much light as possible. In the cat's eyes, the pupil muscles also relax in a dim light and contract to shut out excessively bright light.

But its muscles are not circular. Each is a pair of parallel bands joined at the top and bottom into tapering tips. On a sunny day these slit pupil muscles can close together to shut out all but the smallest pinpoint of light. The cat can protect its eyes better than we can from brilliant sunshine,

The cat also has reflectors in the back of its eyes and human eyes do not. In a dim light l these reflectors bounce back the light that enters its eyes, making some of it enter a second time. This enchance the picture it sees by making the bright areas doubly bright and the dark areas doubly dark: the cat can indeed see better than we can in a dim light, but neither we nor it can see with no light at all. in the dim darkness, the cat's eyes often shine with a eerie glow this eyeshine is not meant to scare its enemies or to give fair warning to its mousy victims: it is Merely the light bouncing back from those reflectors that help it to see better than we Do when the light is dim.