"That's pretty hard to remember," said Nat; "but I know how a soap-bubble looks, though I never saw any birds look that way. Please show us one."
"I will show you two," answered the Doctor, who then went to his glass case, and took out a Wild Pigeon and a Hummingbird. "Look at the shining tints on the neck of this Pigeon, and see how the throat of this Hummingbird glitters when I turn it to the light."
"That's the prettiest color I ever saw," said Nat, "and I can remember about it now. But," he added, thinking of the way he had seen hens mope when they were moulting, "does it hurt birds to lose their feathers, uncle?"
"It is probably not as comfortable as being nicely dressed, and sometimes they seem quite miserable, especially if they shed old feathers faster than new ones can grow to replace the lost ones. Some birds, like Ducks, lose their wing-feathers all at once, and cannot fly for quite a while. But Heart of Nature is kind to his children, as a rule. Most birds shed their rowing feathers one at a time in each wing, so that they never lose their power of flight. Now this will do for wings, tails, and feathers. Come! what is the next thing you notice about this Sparrow? Is it entirely covered with feathers?"
"Of course it isn't," said Dodo; "it hasn't any feathers on its beak or on its feet, else how could it eat and hop about?"
"That is right. These parts of a Sparrow are bare; they never have any feathers; and the skin on them is hard and horny, as different from soft thin skin as finger-nails. Now look at the beak, and think how many things a Sparrow has to do with it. He has no hands or paws, and so he must pick up everything he eats with his beak. He has no teeth, and so he must bite his food with his beak. He feeds on seeds like a Canary bird; so his beak comes to a sharp point, because seeds are small things to pick up; and it is very strong and horny, because seeds are hard to crack, to get at the kernel. Notice, too, children, that his beak is in two halves, an upper half and a lower half; when these halves are held apart his mouth is open, so that you can see the tongue inside; and when the two halves are closed together the mouth is shut. These halves are called the _upper mandible_ and the _lower mandible_."