6oo 
SHIP-WORM. 
be discovered ; but sufficient to admit the surround- 
ing element, and which the animal can regulate by 
the posterior valves.” 
I he animal, in its operations, instinctively fol- 
lows the grain of the wood, and never bores across 
it if the difficulty can possibly be avoided ; for, after 
having penetrated a little way, it turns and con- 
tinues nearly in a parallel direction till it is ob- 
structed either by a knot in the wood or another 
workman of its own species: its course then de- 
pends entirely on the nature of the obstacle; and, if 
the resistance is not to be overcome, it will make 
a short turn in the form of a syphon, rather than 
bore any distance across the grain. 
Mr. Montague examined a great number of these 
shells in the dock-yard of Plymouth, where every 
means have been tried to prevent their destructive 
operations. The piles, he examined, had been re- 
cently taken up to be replaced with new ; these, he 
was informed, had not been under water above four 
or five years, and were in that time greatly perfo- 
rated, though made of sound and solid oak. This 
rapid destruction in the timbers has suggested the 
propriety of the method now adopted in the dock- 
yards to secure them. All that part which is con- 
tinually under water, is covered with short broad- 
headed nails, which the sea salt soon converts into 
a strong coating of rust, impenetrable to these ani- 
mals, and even said to be superior to a sheath ino- 
of copper. 
