as a wink" whenever anything seems likely to fly or splash into them,
and this is what the eyelids are for. If anything gets into the eye
before the lids can shut, the eye "waters," and _tears_ pour out of
it. These are made by a gland-sponge up under the upper lid, so as to
wash any dust or sand or other harmful speck out of the eye before it
can hurt the sensitive eyeball.

Now look at some one's eyeball. It is like the picture, isn't
it?--bright white around the edge and then a ring of color, brown or
blue or gray; and inside the color-ring, or _iris_, a little round
black hole that we call the _pupil_. Watch the little hole change as
you turn the face toward the window. It becomes ever so much smaller.
Now turn the face away from the window, back again into the shadow.
How did the pupil change this time?

[Illustration: EYES PROTECT THEMSELVES AGAINST THE LIGHT]

The iris, or color-ring, acts like a curtain, like the ring-shutter of
a camera, and closes up the hole, or pupil, when the light is too
bright and would dazzle or burn the inside of the eye; but when the
light is dim, the iris opens again, so as to let in light enough with
which to see. Look at the little window in your kitten's eyes. It is
not the same shape as yours; but when you carry her to the light, you
see how the iris closes in and leaves just a little black slit or
line.

You remember the blind children? Isn't it wonderful how they can play
games and study, too, even though they are blind! They have to make
their senses of touch and hearing tell them many things that you learn
through your sense of sight. Many of these children _need not have