You know a good many very different things are called teeth--those on a rake, for example, or a comb, or a cog-wheel.

A Duck's teeth are horny like the skin that covers its whole beak, and act like strainers.

When a Duck dabbles in the water, as you have all seen tame ones do, the water that gets into its mouth runs out at the sides between the teeth, but whatever food there is in the mouthful of water gets caught in the teeth, and can then be swallowed." "Please tell us," continued Rap, "how many different kinds of Ducks there are in our country ?" "About forty," answered the Doctor; "but I shall not trouble you to learn more than a few of the common ones.

They all belong to one family, which also contains the Geese and Swans.

They are divided into three groups--Fishing Ducks, River or Fresh-water Ducks, and Sea Ducks.
"The Fishing Ducks are great swimmers and divers, living chiefly on the fish they catch by chasing them under water.