How few even among lovers of Nature know why a frog has no tail! The
reason-is simply that it used that organ up when it was in want. In
early life, as a jolly tadpole, it had a flourishing tail to swim with,
and gills for breathing water, and an infantile mouth for taking
vegetable nourishment. But when it began to draw near to frog's estate,
serious changes were required in its structure to fit it for the life of
a land animal. Four tiny legs appeared from under its skin, the gills
gave place to air-breathing lungs, and the infant lips to a great,
gaping mouth. Now, during this "temporary alteration of the premises"
all business was of necessity stopped. The half-fish, half-frog could
neither sup like an infant nor eat like a man. In this extremity it fed
on its own tail--absorbed it as a camel is said to absorb its hump when
travelling in the foodless desert--and so it entered on its new life
without one.

Aeronautics have changed the whole perspective of life for birds, as
they may for us shortly; so it is no surprise to find that birds have,
almost with one consent, converted their tails into steering-gear. A
commonplace bird, like a sparrow, scarcely requires this except as a
brake when in the act of alighting; but to those birds with which flight
is an art and an accomplishment, an expansive forked or rounded tail
(there are two patents) is indispensable. We have shot almost all the
birds of this sort in our own country, and must travel if we would enjoy
that enchanting sight--a pair of eagles or a party of kites gone aloft
for a sail when the wind is rising, like skaters to a pond when the ice
is bearing. For an hour on end, in restful ease or swift joy, they trace
ever-varying circles and spirals against the dark storm-cloud, now
rising, now falling, turning and reversing, but never once flapping
their widespread pinions.