"See! here is one," continued the Doctor, as he twitched out a feather from the Sparrow's back. "You see the quill part runs in the middle from one end to the other; this is called the _shaft_. On each side of it all along, except just at the root, the spray-like parts grow. They are called the _webs_ or _vanes_. Now look through this magnifying glass at the web."
The children looked in turn, and each, exclaimed in wonder at the sight.
"Yes, it is very wonderful. The web, that looks so smooth to the naked eye, is made up of a great many small shafts, called _barbs_, that grow out of the main shaft in rows. Every one of these small side-shafts has its own rows of still smaller shafts; and these again have little fringes along their edges, quite curly or like tiny hooks, that catch hold of the next row and hold fast. So the whole feather keeps its shape, though it seems so frail and delicate."
"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_."