A DOG of a taciturn disposition said to his Tail:

  "Whenever I am angry, you rise and bristle; when I am pleased, you
wag; when I am alarmed, you tuck yourself in out of danger.  You
are too mercurial - you disclose all my emotions.  My notion is
that tails are given to conceal thought.  It is my dearest ambition
to be as impassive as the Sphinx."

  "My friend, you must recognise the laws and limitations of your
being," replied the Tail, with flexions appropriate to the
sentiments uttered, "and try to be great some other way.  The
Sphinx has one hundred and fifty qualifications for impassiveness
which you lack."

  "What are they?" the Dog asked.

  "One hundred and forty-nine tons of sand on her tail."

  "And - ?"

  "A stone tail."