ven the eggs, of gigantic
birds have been found. One of these eggs was over a foot in length, and
contained more than ten quarts or as much as six ostrich eggs or one
hundred and fifty hen's eggs. A nearly complete skeleton of one of these
birds has been found, and this must have belonged to a bird fifteen feet
high, or taller than the largest elephant!

The next order includes the wading birds such as the snipe, plover,
woodcock, heron, and rail.

Another order is that of the gulls, ducks, geese, pelicans, penguins,
and other swimming birds.

Besides these living birds, fossil birds have been found in the rocks.
Some of these are very different from any species now living, and very
much like reptiles, so that it is not easy to decide whether they are to
be called birds or reptiles.

The chief peculiarity of birds is their power of flight, and, although
there are a few birds which do not fly, most of them do, and the various
organs of their bodies are all constructed in such a way as to fit them
for a life in the air. Their bodies are very solid and compact, in order
that most of their weight shall be near the place where the wings are
attached. The feet, legs, head, and neck are light, and so arranged that
they may be drawn up close to the body while the bird is flying. As the
neck is long and very flexible, the body does not need to be pliant, as
with most creatures having backbones; but it is important that the wings
should have a firm support, so the bones of the back are united. The
body of a bird must also be well protected from the cold; for, as it
ascends and descends through the air, it passes through regions of very
different temperatures, and it must be provided with a thick and warm
covering in order to be able to endure these sudden changes, and one
also which shall be very light and able to shed the water; for,
otherwise, a bird would be unable to fly. The feathers of a bird answer
to all these needs, and are so placed upon the body that they form a
smooth surface which does not catch against the air when the bird is
passing through it. In its rapid ascents and descents, the bird is
exposed to another danger even greater than the sudden changes of
temperature. You all know that air presses in every direction with great
force, and that we do not feel it because there is air in all parts of
our bodies as well as outside them, and the pressure of the air inside
exactly balances that of the outside air. If