with the kinds which bring up earth to the surface in the form of
castings. Hoffmeister says that the species in Germany are not well
known, but gives the same number as Eisen, together with some strongly
marked varieties. {8b}
Earth-worms abound in England in many different stations. Their castings
may be seen in extraordinary numbers on commons and chalk-downs, so as
almost to cover the whole surface, where the soil is poor and the grass
short and thin. But they are almost or quite as numerous in some of the
London parks, where the grass grows well and the soil appears rich. Even
on the same field worms are much more frequent in some places than in
others, without any visible difference in the nature of the soil. They
abound in paved court-yards close to houses; and an instance will be
given in which they had burrowed through the floor of a very damp cellar.
I have seen worms in black peat in a boggy field; but they are extremely
rare, or quite absent in the drier, brown, fibrous peat, which is so much
valued by gardeners. On dry, sandy or gravelly tracks, where heath with
some gorse, ferns, coarse grass, moss and lichens alone grow, hardly any
worms can be found. But in many parts of England, wherever a path
crosses a heath, its surface becomes covered with a fine short sward.
Whether this change of vegetation is due to the taller plants being
killed by the occasional trampling of man and animals, or to the soil
being occasionally manured by the droppings from animals, I do not know.
{9b} On such grassy paths worm-castings may often be seen. On a heath
in Surrey, which was carefully examined, there were only a few castings
on these paths, where they were much inclined; but on the more level
parts, where a bed of fine earth had been washed down from the steeper
parts and had accumulated to a thickness of a few inches, worm-castings
abounded. These spots seemed to be overstocked with worms, so that they
had been compelled to spread to a distance of a few feet from the grassy
paths, and here their castings had been thrown up among the heath; but
beyond this limit, not a single casting could be found. A layer, though
a thin one, of fine earth, which probably long retains some moisture, is
in all cases, as I believe, 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
8