256 



POPULAR CONCHOLOGY. 



The Teredo is almost the only mollusc which is to any 

 extent injurious to mankind, and this is owing to the 

 animal forming its abode in wood which it meets with in 

 the sea, such as dead and floating trees, piles, and even 

 ships : it is worm-shaped, and about six inches long. In 

 making its excavations into the wood, which it does by 

 boring into the substance in the direction of the grain, 

 and lining the tube with shell, each individual is careful 

 to avoid that formed by its neighbour, and often a very 

 thin leaf alone of wood is left between ; it also, when a 

 knot occurs in its path, makes a turn to avoid it. 



A great proof of the manner in which the operations of 

 this little animal may become prejudicial to us was fur- 

 nished some time ago (1730) in Holland. In that country 

 a considerable portion of the land and coast is below the 

 level of high water ; and in order to prevent the irruption 

 of the sea, immense dikes have been constructed along the 

 shore, formed of large masses of sand, and strengthened 

 by large piles driven into the ground : these piles were 

 attacked by the Teredo, and, on examination, were found 

 to be pierced in all directions to such an extent, that, had 

 it not been for a timely discovery of the mischief, the 

 whole of that part of the country might have been over- 

 whelmed by the sea breaking through the enfeebled and 

 worm-eaten defences. 



Mr. Forbes justly remarks, however, that " with the 

 evil comes good, for it acts as a clearer of the seas, break- 

 ing down into small fragments the useless masses of 

 floating timber and fragments of wreck, which might 

 otherwise prove serious and dangerous impediments to 

 navigation." 



Dr. Mantell speaks of fossil remains of the Teredo in 

 the following words : — " The fossil species differ from the 

 recent in the valves being united to the calcareous tube. 



