The tracts over which the cranes travel must be immense, if we only consider that they come all the way from the Eastern Sea. These birds agree by common consent at what moment they shall set out, fly aloft to look out afar, select a leader for them to follow, and have sentinels duly posted in the rear, which relieve each other by turns, utter loud cries, and with their voice keep the whole flight in proper array. During the night, they place sentinels on guard, each of whom hol............