54 
ORGANS OF BREATHING. 
There is another bird even more copiously supplied with 
air than the above, called the Chavana Fidele, in which the 
skin is entirely separated from the flesh, and filled with an 
infinity of small air-cells, the legs and even toes partaking 
of the same singularity, so that it appears much larger than 
it really is, and when pressed by the finger, the skin sinks 
in, hut resists pressure like a foot-hall, or other elastic body. 
The air, in this case, is supposed to assist in producing a 
powerful screaming voice, the bird being a wader, and not 
calculated for lengthened flights. 
Generally speaking, the hones of birds, excepting when 
young, are without marrow, the gradual absorption of which, 
till the hones become a hollow tube, is most easily perceptible 
in young tame Geese, when killed at different periods of the 
autumn and winter. From week to week the air-cells in- 
crease in size, till, as the season advances, the air-hones be- 
come transparent. Towards the close of the summer and 
beginning of autumn, although in external appearance the 
young Goose resembles the parent, no trace of air-cells can 
he discovered in its hones, — the interior being still filled up 
with marrow, which does not entirely disappear till about the 
end of the fifth or sixth month. 
In the Eagle, Hawk, Stork, Lark, and other birds in the 
habit of soaring, the air-cells are very large, particularly 
those in connexion with the wing. On the other hand, in 
Ostriches, or those birds which either never or seldom fly, 
those of the wing are comparatively small; hut as a compen- 
sation, it has been remarked, that as great strength as well 
as lightness is desirable to enable them to run swiftly, their 
hones are almost all of them remarkably hollow. Such 
are some of the advantages derived from this abundant 
supply of air. 
We have alluded to the additional warmth possessed by 
birds, in comparison with other animals, to which this 
greater quantity of air must essentially conduce. We may 
here again refer to the Gannet, which, passing so much of its 
time in the depth of winter, exposed to the severest weather. 
