SHELLS AND MOLLUSCOUS ANIMALS. 203 



The ravages of this animal were so extensive in 

 the dockyard at Plymouth, that in the course of 

 four or five years it became necessary to remove 

 the wood which it had penetrated. The very 

 submersion of Holland has seemed at times pro- 

 bable, from its destructive effects ; and in the 

 years 1731 and 1732, great alarm was excited in 

 the United Provinces, by the discovery that the 

 teredo had so injured the piles which support the 

 banks of Zealand, as to threaten them with entire 

 destruction. Happily, however, after a time, it 

 disappeared, no one could tell why, unless it 

 might be, that the winter having been unusually 

 severe, it was unable to live in that latitude in 

 such extreme cold. 



Linnseus called the teredo the Calamitas navium, 

 and common as it now is in all the seas of Europe, 

 yet it was formerly believed to have been intro- 

 duced into them, during the last century, from 

 the East, though several species are now con- 

 sidered as natives of Britain. On examining the 

 piers and woodwork about our harbours, we shall 

 too often find specimens of this animal embedded 

 in it. Little canals are formed by it in the wood, 

 sometimes one or two feet long, not always 

 straight, but bending according to the grain of 

 the wood. Inside of these the worm-like animal 

 lies enclosed, usually in a shelly case, secreted by 

 its mantle, but to which it is not attached by any 

 muscles. The true shell is at the end of this 

 ivory case, and consists of two valves, by means 

 of which the teredo cuts its entrance into the 

 wood. The body is a long worm-looking object, 

 and is merely an extension of its two siphons, or 

 tubes. Happily, the teredo, like many other 



