CHAP. VII. RAVAGES OF THE TEREDO NAVALIS. 237 



(249.) The last mentioned animals, although ene- 

 mies, are still united together in one work of injury to 

 man. It is a fact, authenticated by the testimony of 

 travellers, and highly probable in itself, that the burst- 

 ing of the artificial banks of rivers in India is in most 

 cases caused by snakes, rats, and other vermin. These 

 embankments are raised for the purpose of keeping the 

 rivers within due bounds during the rainy season, by 

 which large tracts of country are preserved from annual 

 inundation. These banks are the favourite resort of 

 rats and other burrowing animals, which, in no very 

 long process of years, work their way nearly, if not 

 completely, through. Though their burrows may be 

 near the surface, the ultimate effect is much the same. 



(250.) A few species of shelly molluscous animals are 

 sometimes dreadfully destructive. The most formidable 

 is the Teredo navalis, a worm-like animal, which lines 

 with a shelly matter the windings or irregular cavities 

 which it forms in wood or other substances ; its head 

 is armed with a pair of very strong calcareous or shelly 

 jaws, with which it works its way into the substance it 

 inhabits, which is generally the wood of the bottom of 

 ships. About the year 1730, the most flourishing 

 republic in Europe was made to tremble at the name of 

 this seemingly insignificant creature ; the dykes of 

 Holland, during that year, exhibited such marks of 

 decay in many parts, where they had been attacked by 

 these animals, that great apprehensions were entertained 

 of the woodwork giving way.* 



* Shaw's Zool. Lect, ii. p. 169. 



