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?

If we try to commence--as scientific method requires--with a
definition, we stumble on a key, at the very threshold, which opens the
door. For there is no definition of a tail; it is not, in its nature,
anything at all. 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, which a tailor (the pun is unavoidable) would have trimmed
off. And, lo! in this very negativeness lies the whole secret of the
multifarious positiveness of tails. 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, then
the ingenuity of the devices for turning the useless member to account
affords one of the most exhilarating subjects of contemplation in the
whole panorama of Nature. The fishes fitted it up at once as a
twin-propeller, with results so satisfactory that the whale and the
porpoise, coming long after, adopted the invention. And be it noted that
these last and their kin are now the only ocean-going mammals in the
world. The whole tribe of paddle-steamers, such as seals and walruses
and dugongs, are only coasters.

Among those beasts that would live on the dry land, the primitive
kangaroo could think of nothing better to do with his tail than to make
a stool of it. It was a simple thought, but a happy one. Sitting up