There are mysteries all about us as omnipresent as the movement of the air that lifts the smoke and stirs the leaves. Often and deeply have I been impressed with this. For example, there is scarcely in this world, a commoner or a humbler thing than a tail, yet how multifarious is it in aspect, in construction, and in function, a hundred different things and yet one. Some are of feathers and some of hair, and some bare and skinny; some are long and some are short, some stick up and some hang down, some wag forever and some are still; the uses that they serve cannot be numbered, but one name covers them all. In the course of evolution they came in with the fishes and went out with man. What was their purpose and mission? What place have they filled in the scheme of things? In short, what is the true inwardness of a tail?
When an animal's fore-legs are fitted on to its backbone at the proper distance from the hind- legs, if any of the backbone remains over, we call it a tail. But it has no purpose; it is a mere surplus. And here lies the whole secret of the multifarious use. For the absence of special purpose is the chance of general usefulness. The ear must fulfil its purpose or fail entirely, for it can do nothing else. Eyes, nose and mouth, hands and feet, all have their duties; the tail is the unemployed. And if we allow that life has had any hand in the shaping of its own destiny.