necessary for their existence; and the mere compression of the soil
appears to be in some degree favourable to them, for they often
abound in old gravel walks, and in foot-paths across fields.

Beneath large trees few castings can be found during certain
seasons of the year, and this is apparently due to the moisture
having been sucked out of the ground by the innumerable roots of
the trees; for such places may be seen covered with castings after
the heavy autumnal rains. Although most coppices and woods support
many worms, yet in a forest of tall and ancient beech-trees in
Knole Park, where the ground beneath was bare of all vegetation,
not a single casting could be found over wide spaces, even during
the autumn. Nevertheless, castings were abundant on some grass-
covered glades and indentations which penetrated this forest. On
the mountains of North Wales and on the Alps, worms, as I have been
informed, are in most places rare; and this may perhaps be due to
the close proximity of the subjacent rocks, into which worms cannot
burrow during the winter so as to escape being frozen. Dr.
McIntosh, however, found worm-castings at a height of 1500 feet on
Schiehallion in Scotland. They are numerous on some hills near
Turin at from 2000 to 3000 feet above the sea, and at a great
altitude on the Nilgiri Mountains in South India and on the
Himalaya.

Earth-worms must be considered as terrestrial animals, though they
are still in one sense semi-aquatic, like the other members of the
great class of annelids to which they belong. M. Perrier found
that their exposure to the dry air of a room for only a single
night was fatal to them. On the other hand he kept several large
worms alive for nearly four months, completely submerged in water.