4 
BIRD-LIFE. 
every bone in the body is filled with air; while in other 
birds there are only one or two bones thus hollow. This 
faculty of distributing the air inhaled throughout the 
body has been called in German “ Pneumaticitat ” (that 
is to say, the power of inflating with air) ; it is peculiar 
to this class of birds. Its use is easily discernible; the 
air thus dispersed through its frame is warmed by the 
body and expands, so as to make it more buoyant, and, 
at the same time, facilitate respiration under the most 
varied pressures of atmosphere : thus it assists flight. 
A second absolutely indispensable appendage of the 
bird is its feathers: these (as the proverb has long told 
us) make the bird what it is;—a bird. The feather 
combines in itself all the following necessary qualities :— 
lightness, compactness, with slight heat-conducting power, 
durability, elasticity and beauty. It is one of the marvels 
of creation,—like the eye ; either of which only yields its 
secrets to the closest scrutiny. He who examines a 
feather under the microscope sees before him a master¬ 
piece of mechanism. The feather is a product of the 
outer skin or epidermis, quite as much as the hair of a 
mammal or the scales of a lizard; but it differs vastly 
from both. It consists, as all know, of the quill, the 
shaft, and two webs or fringes : these webs are precisely 
the portions which demand the most careful observation, 
inasmuch as but few persons are aware of their com¬ 
ponent parts. 
Each web, even of the smallest feather, shows a 
twofold repetition of the original form of the feather in 
its innumerable separate parts. It consists of other 
webs: these are attached to shafts, and bear a second 
row of webs, or rather filaments; and, lastly, these are 
bordered with cilia. 
