blackbird and a starling are both tidy birds, and both walk much on the
ground, but the one lifts its skirts, while the other, more practical
and less fashionable, wears a walking dress and saves itself trouble.

This line of observation leads to a higher, and reveals the most
important purpose that tails have served in the economy of beast, bird,
and reptile, and, perhaps, even cold-blooded fish. Before the godlike
countenance of man appeared on the earth, with its contractile forehead
and erectile eyebrows, the answering light of the eye, the expansive
nostrils, and subtilely mobile lips; before that the tail was the prime
vehicle of emotion and safety-valve of passion. It is a great truth, too
often buried in these days under rubbish of materialistic theories, that
some way of self-manifestation is a supreme necessity of all sentient
life. From the hot centre of thought and feeling the currents rush along
the nervous ways and pervade the whole frame, seeking an outlet. But
many passages are barred by duty, or fear, or eager purpose. A strong
gust of passion may burst all barriers and force its way out at every
point, but gentle currents flow along the lines of least resistance and
find the idle tail. I do not know a better illustration of this than a
cat watching a mouse. The ears are pricked forward, the eyes are fixed
on the unsuspecting victim, every muscle of the legs is tense, like a
bent bow ready to speed the arrow on its way. But see, the excitement
with which the whole body is charged cannot be wholly restrained, and
oozes out at the point of the tail.

[Illustration: AT THE SIGHT OF A RIVAL THE DOG HOLDS ITS TAIL UP
STIFFLY]

Every emotion and passion takes this course. The happy kid wags its tail
as it runs to its mother, the donkey when it has executed a successful