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90 But after watching them now, for some two hours, I should doubt if they ever 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