Nancy Lee, age 10, of Oshowa, Ontario, Canada, for her question:

Why is there no coral in lakes?

A few creatures can live either in salt water or fresh water, but most water dwellers must choose to spend their lives in either the salty sea or in the fresh lakes and rivers. Crusty coral is made by small marine creatures who can live only in the salty sea. They would fail to survive in the fresh waters of a lake. Certainly they could never endure the chilly winter water of the Great Lakes. The little creatures love trorical and semitropical waters and they cannot live in water that gets colder than 65 degrees Fahrenheit.

A pretty piece of crusty coral was once the home of many small coral animals. Each little creature added a room of his own to the family tree. He built it from limestone sifted from sea water and he lived in it all his life. He was a soft polyp animal, a cousin of the jelly fishes and the dainty sea anemones. A piece of rocky coral is the apartment house for him and his kinfolk. But all the soft little polyps perish when it is taken out of the warm, salty sea.