.
144
_
THESEAS
"
as though the animals must comme Out of their burfows as
'
in size and start new ones. .Another way in
.
which the Gribble dierS from the Shipworm is that it is
always the fully—grown animals which start new burrows.
To do this,» they rst
of all hollow out a groove along
”
-'
surface, keeping in the soft part of the grain, and then
_
_
pass
a
very easy incline into the wood.
Usually the
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FXG.
31.—-‘—Mandibles of the Gribble‘, Lîmnoria, showing “ reisp-and-le ”
'
_
_
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._
combination, greatly enlarged
.
,
burrows_are not deep the need for obtaining a constant '
supply of _freSh sea water probably controls
and, ..
though they have been found as' deep as
of an
,
'
below the
they do
not usually pènetrate 'f01‘
more than a third of this distanCe. The burro‘ws
aref
often three-quarters “of an inch or more in length;
It
‘is easy to follow
the course of a burrow from above be‘—
,