"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."