“Are all feathers like this one?” asked Rap.

“All are equally wonderful, and equally beautiful in construction; but there is a good deal of difference in the way the webs hold together.  Almost all feathers that come to the surface are smooth and firm, and there is not much difference except in size, or shape, or color.  For example, the largest wing-feather or tail-feather of this Sparrow is quite like the one I pulled out of its back in texture, only the back-feather is smaller and not so stiff.  But near the roots of these feathers you notice a fluffy part, where the webs do not hold together firmly.  Some feathers are as fluffy as that in their whole length.  Such are called down-feathers, because they are so downy.  Birds that run about as soon as they are hatched are always clothed in down, like little chickens, before their other feathers sprout; and some birds, like Ducks, wear a warm underclothing of down their whole lives.  Then again some feathers do not have any webs at all—­only a slender shaft, as fine as a hair.”

“Do feathers keep on growing all the time, like my hair?” asked Dodo.

“No, my dear.  They stop growing as soon as they are of the right size; and you will find your hair will do the same, when it is long enough—­though that won’t be for a good many years yet, little girl.  When the blood that has fed the growing feather is all dried up, the feather ceases to grow.  Then after a while longer, when it has become ragged and worn, it gets loose in the skin and drops out—­as I am sorry to say some of my hair is doing already.  That is what we call moulting.”

“I know about that,” interrupted Nat.  “It’s when hens shed their feathers.  But I didn’t know that it was moulting when people grow bald.”

“It is very much the same thing,” said the Doctor, “only we don’t call it moulting when people lose their hair.  But there is this difference.  Birds wear out their feathers much faster than we do our hair, and need a new suit at least once a year, sometimes oftener.  All young birds get their first new clothes when the down is worn out.  Old birds generally moult as soon as they have reared their broods, which in this country is late in summer or early in the fall.  Many also moult again the following spring, when they put on their wedding dress; and one of the curious things about this change of plumage is, that the new feathers often come out quite unlike those that were cast off.  So a bird may differ much in appearance at different seasons and ages—­in fact, most birds do.  The male also differs in many cases from the female, being more handsomely dressed than his mate.”

“I don’t think that’s fair,” said Dodo.  “I shouldn’t like Nat to have nicer clothes than I wear.”