EXCAVATORS. 



341 



no obstacle to its depredations. " The animal always 

 tunnels in the direction of the grain, and if in its 

 course it meets with another, engaged in the same 

 process, it alters the direction of its course, so that 

 a piece of wood attacked by many Teredos becomes 

 completely honey-combed." In the 

 beginning of the century, half the coast 

 of Holland was threatened with the 

 invasion of the sea, because the piles, 

 which upheld the dykes, were attacked 

 by the Teredo ; and it required an out- 

 lay of a large sum of money to secure 

 the country from the disaster of an 

 inundation, caused by a contemptible 

 mollusk. 



" The body of the Teredo is long and 

 worm-like ; its colour greyish-white (fig. 

 66). At one end is a knot, improperly 

 called its head, and the other extremity 

 bifurcates into what may be called two 

 tails. It often attains the length of 

 eight inches. It buries itself in a case, 

 which it eats out of the wood ; the 

 walls of the case are covered with a coating of a 

 calcareous matter mixed with mucus ; this renders 

 them firm and solid. The round part of the mol- 

 lusk carries two small valves, very thin and fragile ; 

 they are not unlike in shape to two halves of a 



FIG. 66 



( Teredo navalis} 



