34 The Bird 
re) 
upward and escape beyond the edge. So it would, if it 
were not for the arrangement of the feathers on the wing, 
which overlap like the tiles on a roof, each vane over- 
lying and holding down the long barbs of the feather 
in front, while, above and below, other shorter feathers 
help to bind the whole tightly, thus enabling the bird at 
every stroke to whip a wingful of air downward and 
backward. 
A feather and its parts, like all the rest of the bird, is 
composed of cells—empty and hollow ones in this in- 
stance, as we can easily see for ourselves by placing a 
barb from a pigeon’s feather in a drop of water and 
looking at it under a low-power magnifying-lens. The 
network of horny cells is very plain. 
It is a simple matter to say that a feather consists of 
quill, barb, barbules, etc., but to appreciate the wonder- 
ful complexity of this structure let us make a little cal- 
culation. Suppose we have a wing-feather from a com- 
mon pigeon with a vane about six inches long. If we 
have patience enough to count the barbs on one side of 
the quill, we will find there are about six hundred of 
them. So the vane of the entire feather has twelve 
hundred of these little side featherlets. One of these, 
from a narrow part of the vane, will show under the micro- 
scope about two hundred and seventy-five pairs of bar- 
bules, which multiplied by the number of barbs on that 
side amounts to three hundred and thirty thousand. 
Making a very low estimate of the whole vane, we have 
nine hundred and ninety thousand separate barbules on 
this one feather, and when we think of the innumerable 
