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.
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