hteen inches in
diameter, which was filled with sand, on which fallen leaves were
strewed; and these were soon dragged into their burrows to a depth
of three inches. After about six weeks an almost uniform layer of
sand, a centimetre (.4 inch) in thickness, was converted into humus
by having passed through the alimentary canals of these two worms.
It is believed by some persons that worm-burrows, which often
penetrate the ground almost perpendicularly to a depth of five or
six feet, materially aid in its drainage; notwithstanding that the
viscid castings piled over the mouths of the burrows prevent or
check the rain-water directly entering them. They allow the air to
penetrate deeply into the ground. They also greatly facilitate the
downward passage of roots of moderate size; and these will be
nourished by the humus with which the burrows are lined. Many seeds
owe their germination to having been covered by castings; and others
buried to a considerable depth beneath accumulated castings lie
dormant, until at some future time they are accidentally uncovered
and germinate.

Worms are poorly provided with sense-organs, for they cannot be said to
see, although they can just distinguish between light and darkness; they
are completely deaf, and have only a feeble power of smell; the sense of
touch alone is well developed. They can therefore learn little about the
outside world, and it is surprising that they should exhibit some skill
in lining their burrows with their castings and with leaves, and in the
case of some species in piling up their castings into tower-like
constructions. But it is far more surprising that they should apparently
exhibit some degree of intelligence instead of a mere blind instinctive
impulse, in their manner of plugging up the mouths of their burrows.
They act in nearly the same manner as would a man, who had to close a
cylindrical tube with different kinds of leaves, petioles, triangles of
paper, etc., for they commonly seize such objects by their pointed ends.
But with thin objects a certain number are drawn in by their broader
ends. They do not act in the same unvarying manner in all cases, as do
most of the lower animals; for instance, they do not drag in leaves by
their foot-stalks, unless the basal part of the blade is as narrow as
the apex, or narrower than it.

When we behold a wide, turf-covered expanse, we should remember that its
smoothness, on which so much of its beauty depends, is ma