sprouts. It grows in a sheath that pushes out of the hole, like a plant
coming up out of the ground from its root. For a while this sheath is
full of blood to nourish the growing feather; that is why new feathers
look dark and feel soft--pin-feathers they are called. The blood dries
up when the feather has unfolded to its full size, leaving it light and
dry, with a horny part at the root that sticks in the hole where it
grew, and a spray-like part that makes up most of the feather. The horny
part becomes hollow or contains only a little dry pith; when it is large
enough, as in the case of a rowing feather from a Goose's wing, it makes
a quill pen to write with. But the very tiniest feather on this Sparrow
is built up in the same way.

"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.