“Something the way frogs’ feet are?” asked Nat.

“Very much upon the same plan.  Then Ducks have wide flat beaks of various shapes, with a sort of nail bent over like a hook at the end, and all along each side is a double row of little teeth, to help them take their food.  Their stiff, pointed wings are quite strong enough to lift their heavy bodies off the ground or water into the air, and keep up an even flight, often more rapid than the swiftest express train.”  “What do Wild Ducks eat?” asked Dodo, “seeds or bugs or fish?”

“They eat all those things and many others too, according to their various habits, which are as different as the expression of their faces or the color of their features.  If you look at a case full of Wild Ducks in a museum, you will find that no two have the same-shaped head, or expression.  Some look silly, some sly, while others seem either proud or inquisitive.”

“How strange!” said Rap.  “I never thought about Ducks’ faces, except that they all looked foolish, with little pig-eyes and big beaks like shovels.  And please, do they chew their food with the teeth you said they had?”

“Those are not true teeth, like ours, to chew with.  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.  Their beaks are narrow, hooked, and sharply toothed, which makes it easy for them to hold their slippery prey.  But this oily food makes their flesh so rank that none of them is fit food for House People.  They are all called Mergansers, and we have in this country four different species.

“The River Ducks are those that we see mostly in the spring and fall migrations; they have the handsomest plumage and the most delicate flesh.  They feed along shallow rivers, ponds, and lakes, after the manner of barnyard Ducks—­for the Mallard is one of them, and tame Ducks are domesticated Mallards, as I told you.  In feeding, they bob head downward in the water with their tails straight up in the air, to find the roots, seeds, insects, small shell-fish, and other things they like to eat.  They build