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Why do cats' eyes contract to a vertical slit?
Cats evolved to be nocturnal hunters, and they can see well
in very dim light. Because their eyes are so sensitive to
light, cats need precise control over the amount of light
reaching their eyes.
Being able to reduce the pupils to slits rather than tiny
circles gives the cat greater and more accurate control of
how much light enters their eyes; this ability is particularly important in bright sunlight.
Vertical slits also have an advantage over horizontal slits.
Because the cat's eyelids close at right angles to the
vertical pupil, the cat can reduce the amount of light even
further by bringing its eyelids closer and closer together.
This combination of the vertical slits of the pupils and the
horizontal slits of the eyelids, allows the cat to make the
most delicate adjustments of the light reaching its eye
compared to any other animal.
The pupils of the lion are an interesting comparison. The
lion hunts by day, not by night as the cat does. The lion
does not have the same sensitivity to light as the cat.
And the lion's eyes contract -- like ours do -- to tiny
circles, not vertical slits.
-- Unknown
I wish I could write as mysterious as a cat. Edgar Allan Poe
Newborn kittens have closed ear canals that don't begin to open for nine days. When the eyes open, they are always blue at first. They change color over a period of months
to the final eye color.
