THE MUSSEL 41 



themselves down by means of a bundle of very 

 strong threads, which we call the " byssus " ; and 

 these hold so firmly, that although the waves 

 may beat upon a bed of mussels day after day 

 all through the year, they never succeed in tear- 

 ing them away. 



Near the town of Bideford in Devonshire, in- 

 deed, there is a bridge which is only kept stand- 

 ing by means of mussels. This bridge, which is a 

 very long one, with twenty-four arches, runs across 

 the Towridge River, close to the place where it 

 joins the Taw ; and the tide runs so rapidly that 

 if mortar is used to repair the bridge it is very 

 soon washed away. So boat-loads of mussels are 

 brought to the bridge from time to time, and these 

 anchor themselves down so firmly by means of 

 their byssus threads that they actually hold the 

 stone-work together ! 



Sometimes, however, mussels do a great deal 

 of harm, for they will get into an oyster-bed and 

 fasten themselves down upon the shells of the 

 oysters. Their byssus threads then form a kind 

 of thick mat, which collects and holds the mud 

 that is brought up by the tide every time that 

 it rises; and this very soon covers the oysters 

 entirely up, and smothers them to death. 



Mussels do not remain fastened down in one 

 place for the whole of their lives, however, as 

 oysters do. They can crawl about quite easily 

 whenever they like. And they do this, also, by 



