rding the notes of all the rest. Persons; however, who
have an accurate ear, and who have given their attention to the songs of
birds, can frequently distinguish some which have their notes mixed with
those of another species; but this is in general so trifling, that it
can hardly be considered as more than the mere varieties of provincial
dialects.

923. IN REFERENCE TO THE FOOD OF BIRDS, we find that it varies, as it
does in quadrupeds, according to the species. Some are altogether
carnivorous; others, as so many of the web-footed tribes, subsist on
fish; others, again, on insects and worms; and others on grain and
fruit. The extraordinary powers of the gizzard of the granivorous
tribes, in comminuting their food so as to prepare it for digestion,
would, were they not supported by incontrovertible facts founded on
experiment, appear to exceed all credibility. Tin tubes, full of grain,
have been forced into the stomachs of turkeys, and in twenty-four hours
have been found broken, compressed, and distorted into every shape.
Twelve small lancets, very sharp both at the point and edges, have been
fixed in a ball of lead, covered with a case of paper, and given to a
turkey-cock, and left in its stomach for eight hours. After that time
the stomach was opened, when nothing appeared except the naked ball. The
twelve lancets were broken to pieces, whilst the stomach remained
perfectly sound and entire. From these facts, it is concluded that the
stones, so frequently found in the stomachs of the feathered tribes, are
highly useful in assisting the gastric juices to grind down the grain
and other hard substances which constitute their food. The stones,
themselves, being also ground down and separated by the powerful action
of the gizzard, are mixed with the food, and, no doubt, contribute very
greatly to the health, as well as to the nourishment of the animals.

924. ALL BIRDS BEING OVIPAROUS, the eggs which they produce after the
process of incubation, or sitting for a certain length of time, are, in
the various species, different both in figure and colour, as well as in
point of number. They contain the elements of the future young, for the
perfecting of which in the incubation a bubble of air is always placed
at the large end, between the shell and the inside skin. It is supposed
that from the heat communicated by the sitting bird to this confined
air, its spring is increased beyond its natural tenor, and, at the same
time,