90 CLASS CONCHIFERA. 



course it generally excavates in the direction of the 

 grain of the wood, but in some instances it crosses this 

 grain. 



In Holland a great part of the country is below the 

 level of high water, and, to prevent the irruption of the 

 sea, immense dykes have been formed along the coast ; 

 these are framed, on the sea-side, of large masses of sand, 

 while to the landward they are strengthened by means 

 of strong piles driven into the ground and wattled toge- 

 ther. These piles were once discovered pierced in all 

 directions by this destructive worm, to such an extent 

 as to endanger their safety, and had it not been for a 

 timely discovery of the mischief, immense tracts of 

 country would have been laid under water, and irre- 

 trievablv lost. 



