Kathy Hurley, age 11, of Rochester, N.Y.,for her question:

How does an earthworm tell light?

Without a doubt, the earth worm is a small miracle. He manages to get around without legs, wings or fins. He manages to tell the difference between daylight and darkness without any definite eyes. Actually he does not see a clear picture of the world. But he has a number of light sensi¬tive cells that tell him all he needs to know. These special cells are buried in his skin, and fine nerves connect them tothe major nerve that runs along the length of his body.

There are no light sensing cells on his underside, where they would be useless. Most of them are at his head end and his tail end. If the sun is shining outdoors, these sensitive cells react when he pokes either end out of his burrow. When they report bright sunshine the worm wriggles back home, because he is more comfortable in the darkness down in his burrow.