90 THE BIRD WATCHER 
But after watching them now, for some two hours, 
I should doubt if the¥"ver moved more than an inch 
or so beyond an imaginary line drawn close round 
them, as they lie. Here natural selection seems 
a demonstrable thing, for often, were the chick to 
move so much as six inches forward, or a few feet 
in any other direction, it must fall and be dashed to 
pieces. What but this force—-or, rather, process— 
can have produced such a want of all inclination to 
move? It is the same, I suppose, with birds that 
nest in trees or bushes. With the nightjar, however, 
though the chicks become, after a while, somewhat 
active, so that the nest, or rather nursery, is shifted 
from day to day, yet for some time they lie very 
quiet, though well able to run about. Here the 
above explanation does not apply, so that one can 
never be sure. ‘ Theories,” says Voltaire “are like 
mice. They run through nineteen holes, but are 
stopped by the twentieth.” Still, it would generally 
be an advantage for young birds to keep still when 
left by themselves, even in a field or wood, and how 
much more so where a step or two, or one little run, 
would be death. Looking at these fat, fluffy, odd- 
looking creatures as they sit motionless from hour to 
hour, and then at the grown bird sailing on spread 
wings, all grace and beauty,—-a being that seems born 
of the air—the change from one to the other—from 
the fixed to the free phase of life—seems hardly less 
or more remarkable than that by which a chrysalis 
becomes a butterfly. Not the egg itself differs more 
