7th and 19th of the same year, much rain having fallen during the latter
part of this time. During frosts and thaws the movements were twice as
great. These observations were made by my son Horace, who will hereafter
publish an account of the movements of this stone during successive wet
and dry seasons, and of the effects of its being undermined by worms.
Now when the ground swells, if it be penetrated by cylindrical holes,
such as worm-burrows, their walls will tend to yield and be pressed
inwards; and the yielding will be greater in the deeper parts (supposing
the whole to be equally moistened) from the greater weight of the
superincumbent soil which has to be raised, than in the parts near the
surface. When the ground dries, the walls will shrink a little and the
burrows will be a little enlarged. Their enlargement, however, through
the lateral contraction of the ground, will not be favoured, but rather
opposed, by the weight of the superincumbent soil.
_Distribution of Worms_. Earth-worms are found in all parts of the world,
and some of the genera have an enormous range. {113} They inhabit the
most isolated islands; they abound in Iceland, and are known to exist in
the West Indies, St. Helena, Madagascar, New Caledonia and Tahiti. In
the Antarctic regions, worms from Kerguelen Land have been described by
Ray Lankester; and I found them in the Falkland Islands. How they reach
such isolated islands is at present quite unknown. They are easily
killed by salt-water, and it does not appear probable that young worms or
their egg-capsules could be carried in earth adhering to the feet or
beaks of land-birds. Moreover Kerguelen Land is not now inhabited by any
land-bird.
In this volume we are chiefly concerned with the earth cast up by worms,
and I have gleaned a few facts on this subject with respect to distant
lands. Worms throw up plenty of castings in the United States. In
Venezuela, castings, probably ejected by species of Uroch ta, are common
in the gardens and fields, but not in the forests, as I hear from Dr.
Ernst of Caracas. He collected 156 castings from the court-yard of his
house, having an area of 200 square yards. They varied in bulk from half
a cubic centimeter to five cubic centimeters, and were on an average
three cubic centimeters. They were, therefore, of small size in
comparison with those often found in England; for six large castings from
a field near my house averaged 16 cubic centimeters. Several species of
earth-worms are common in St. Catharina in South Brazil, and Fritz Muller
informs me that in most parts of the forests and pasture-lands, the
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