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with their respiration which is effected by the skin alone。
A worm after swallowing earth； whether for making its burrow or for
food； soon comes to the surface to empty its body。 The ejected
earth is thoroughly mingled with the intestinal secretions； and is
thus rendered viscid。 After being dried it sets hard。 I have
watched worms during the act of ejection； and when the earth was in
a very liquid state it was ejected in little spurts； and by a slow
peristaltic movement when not so liquid。 It is not cast
indifferently on any side； but with some care； first on one and
then on another side； the tail being used almost like a trowel。
When a worm comes to the surface to eject earth； the tail
protrudes； but when it collects leaves its head must protrude。
Worms therefore must have the power of turning round in their
closely…fitting burrows； and this； as it appears to us； would be a
difficult feat。 As soon as a little heap has been formed； the worm
apparently avoids； for the sake of safety； protruding its tail； and
the earthy matter is forced up through the previously deposited
soft mass。 The mouth of the same burrow is used for this purpose
for a considerable time。 In the case of the tower…like castings
（see Fig。 2） near Nice； and of the similar but still taller towers
from Bengal （hereafter to be described and figured）； a considerable
degree of skill is exhibited in their construction。 Dr。 King also
observed that the passage up these towers hardly ever ran in the
same exact line with the underlying burrow； so that a thin
cylindrical object such as a haulm of grass； could not be passed
down the tower into the burrow； and this change of direction
probably serves in some manner as a protection。
Worms do not always eject their castings on the surface of the
ground。 When they can find any cavity； as when burrowing in newly
turned…up earth； or between the stems of banked…up plants； they
deposit their castings in such places。 So again any hollow beneath
a large stone lying on the surface of the ground； is soon filled up
with their castings。 According to Hensen； old burrows are
habitually used for this purpose； but as far as my experience
serves； this is not the case； excepting with those near the surface
in recently dug ground。 I think that Hensen may have been deceived
by the walls of old burrows； lined with black earth； having sunk in
or collapsed； for black streaks are thus left； and these are
conspicuous when passing through light…coloured soil； and might be
mistaken for completely filled…up burrows。
It is certain that old burrows collapse in the course of time； for
as we shall see in the next chapter； the fine earth voided by
worms； if spread out uniformly； would form in many places in the
course of a year a layer 0。2 of an inch in thickness； so that at
any rate this large amount is not deposited within the old unused
burrows。 If the burrows did not collapse； the whole ground would
be first thickly riddled with holes to a depth of about ten inches；
and in fifty years a hollow unsupported space； ten inches in depth；
would be left。 The holes left by the decay of successively formed
roots of trees and plants must likewise collapse in the course of
time。
The burrows of worms run down perpendicularly or a little
obliquely； and where the soil is at all argillaceous； there is no
difficulty in believing that the walls would slowly flow or slide
inwards during very wet weather。 When； however； the soil is sandy
or mingled with many small stones； it can hardly be viscous enough
to flow inwards during even the wettest weather； but another agency
may here come into play。 After much rain the ground swells； and as
it cannot expand laterally； the surface rises； during dry weather
it sinks again。 For instance； a large flat stone laid on the
surface of a field sank 3。33 mm。 whilst the weather was dry between
May 9th and June 13th； and rose 1。91 mm； between September 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。 ｛41｝ 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
Urochaeta； 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 whole soil； to a depth of a quarter of a metre；
looks as if it had passed repeatedly through the intestines of
earth…worms； even where hardly any castings are to be seen on the
surface。〃 A gigantic but very rare species is found there； the
burrows of which are sometimes even two centimeters or nearly 0。8
of an inch in diameter； and which apparently penetrate the ground
to a great depth。
In the dry climate of New South Wales； I hardly expected that worms
would be common； bu