THE SHELL-FISH OF THE COAST. 41 
attack the floating cocoa-nut. The rapidly-forming 
burrow follows in a sinuous line the grain of the 
wood, passing out of the way of knots, and con- 
scientiously avoiding the burrows of confederate 
workers. In this manner a piece 
of wood is soon honey-combed. 
The entrance is made by a minute 
hole, the size of the burrow in- 
creasing with the growth of the 
animal, A lining of white calca- 
reous matter usually extends along 
the entire length of the burrow, 
to the farther end of which the 
two valves of the shell are at- 
tached. 
It is well ascertained in the case 
of the ship-worm that the burrow 
is largely, or even principally, ex- 
cavated by shell-abrasion, although 
perhaps the exact process has not 
yet been clearly made out. Large 
quantities of the wood-dust are 
frequently found within the intes- 
tine of the animal, and it appears 
not unlikely that some of it is 
intentionally swallowed, and even 
used for nourishment. The ray- , 
ages of the ship-worm may be such Woop BORED BY 
as to destroy within a very short aah enres 
time the stoutest timber; indeed, it is said that 
piles that had been driven only six or seven weeks 
on the Dutch coast were found at the end of that 
4* 
