of very fine sand over gravel-walks is often plainly marked with
their tracks. I have noticed this from August to May, both months
included, and it probably occurs during the two remaining months of
the year when they are wet. On these occasions, very few dead
worms could anywhere be seen. On January 31, 1881, after a long-
continued and unusually severe frost with much snow, as soon as a
thaw set in, the walks were marked with innumerable tracks. On one
occasion, five tracks were counted crossing a space of only an inch
square. They could sometimes be traced either to or from the
mouths of the burrows in the gravel-walks, for distances between 2
or 3 up to 15 yards. I have never seen two tracks leading to the
same burrow; nor is it likely, from what we shall presently see of
their sense-organs, that a worm could find its way back to its
burrow after having once left it. They apparently leave their
burrows on a voyage of discovery, and thus they find new sites to
inhabit.

Morren states {12} that worms often lie for hours almost motionless
close beneath the mouths of their burrows. I have occasionally
noticed the same fact with worms kept in pots in the house; so that
by looking down into their burrows, their heads could just be seen.
If the ejected earth or rubbish over the burrows be suddenly
removed, the end of the worm's body may very often be seen rapidly
retreating. This habit of lying near the surface leads to their
destruction to an immense extent. Every morning during certain
seasons of the year, the thrushes and blackbirds on all the lawns
throughout the country draw out of their holes an astonishing
number of worms, and this they could not do, unless they lay close
to the surface. It is not probable that worms behave in this
manner for the sake of breathing fresh air, for we have seen that