was 3.3 inches in height and 1 inch in diameter. A small cylindrical
passage runs up the centre of each tower, through which the worm ascends
to eject the earth which it has swallowed, and thus to add to its height.
A structure of this kind would not allow leaves being easily dragged from
the surrounding ground into the burrows; and Dr. King, who looked
carefully, never saw even a fragment of a leaf thus drawn in. Nor could
any trace be discovered of the worms having crawled down the exterior
surfaces of the towers in search of leaves; and had they done so, tracks
would almost certainly have been left on the upper part whilst it
remained soft. It does not, however, follow that these worms do not draw
leaves into their burrows during some other season of the year, at which
time they would not build up their towers.
From the several foregoing cases, it can hardly be doubted that worms
swallow earth, not only for the sake of making their burrows, but for
obtaining food. Hensen, however, concludes from his analyses of mould
that worms probably could not live on ordinary vegetable mould, though he
admits that they might be nourished to some extent by leaf-mould. {102}
But we have seen that worms eagerly devour raw meat, fat, and dead worms;
and ordinary mould can hardly fail to contain many ova, larv , and small
living or dead creatures, spores of cryptogamic plants, and micrococci,
such as those which give rise to saltpetre. These various organisms,
together with some cellulose from any leaves and roots not utterly
decayed, might well account for such large quantities of mould being
swallowed by worms. It may be worth while here to recall the fact that
certain species of Utricularia, which grow in damp places in the tropics,
possess bladders beautifully constructed for catching minute subterranean
animals; and these traps would not have been developed unless many small
animals inhabited such soil.
_The depth to which worms penetrate_, _and the construction of their
burrows_. Although worms usually live near the surface, yet they burrow
to a considerable depth during long-continued dry weather and severe
cold. In Scandinavia, according to Eisen, and in Scotland, according to
Mr. Lindsay Carnagie, the burrows run down to a depth of from 7 to 8
feet; in North Germany, according to Hoffmeister, from 6 to 8 feet, but
Hensen says, from 3 to 6 feet. This latter observer has seen worms
frozen at a depth of 11 2 feet beneath the surface. I have not myself had
many opportunities for observation, but I have often met with worms at
depths of 3 to 4 feet. In a bed of fine sand overlying the chalk, which
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