mouth of the shaft, it elevates its eyes (which in the dark have rested
in neatly fitting recesses) for the purpose of a cautious yet sweeping
survey. Seeing nothing alarming, it emerges with the alertness of a
jack-in-the-box, races several inches, and scatters the load broadcast as
the sower of seed who went forth to sow. Then, as suddenly, the crab
pauses and flattens itself--its body merging with its surroundings almost
to invisibility--preparatory for a spurt for home. During these
exertions the intellect of the crab has been concentrated for outwitting
the vigilance of enemies, for the plodding policeman is not singular in
appreciation. The lordly red-backed sea-eagle occasionally condescends to
such humble fare, and the crab must needs be alert to evade the scrutiny
with which the eagle searches the sand.

This passing reference to the wit and deftness of the crab would be quite
uncomplimentary in default of special notice of the plug of sand with
which it stops its burrow. As a rule it is about an inch thick, and in
content far more than a crab could carry in a single load. How does the
creature, working from below and with such refractory material, so
arrange that the plug shall be flush with the surface and sufficiently
consolidated to retain its own weight? Of what art in loose masonry has
the crab the unique secret? Shakespeare speaks of stairs of sand, and Poe
laments the "how few" grains of golden sand which crept through his
fingers to the deep; but who but a crab possesses the secret for the
building of a roof of the material which is the popular emblem of
instability and shiftiness?

The impartial student must not restrict his notions as to the
possibilities of sand to the admirable accomplishments of crabs. He may
also inspect with profit the handicraft of a lowly mollusc which
agglutinates sand-grains into a kind of plaque, in the substance of