The locomotion of animals, as exemplified in walking, swimming, and flying, is a subject of permanent interest.

The three modes of progression, apparently so unlike, are nevertheless essentially the same. The limbs of the quadruped, the wings of the bird, and the fins of the fish, are built upon the same general plan of structure, and are applied fundamentally to the same uses. They are traveling surfaces, and their wide range of modification is in direct relation to the media in which they are used. They are traveling surfaces, and their wide range of modification is in direct relation to the media in which they are used. The one treads the solid ground, another the water, and another the yielding and elastic air...

From the researches and experiments, it will be evident that a remarkable analogy exists between walking, swimming, and flying.