MUSSELS. 



73 



byssus, and fastening themselves firmly to the 

 solid support. 



And so you can often find the side of a ledge 

 that faces the sea almost covered with mussel- 

 shells, set as closely as they can lie, and all so 

 firmly anchored by the horny threads that you 

 can hardly pull off one shell at a time. 



When the tide comes in, you can see why they 

 need these strong anchor-chains, for the waves 

 will sweep up and down the face of the ledge, 

 washing away everything that 

 is not fastened in the securest 

 manner. 



But this dashing of the 

 waves is just what the mussels 

 enjoy. They know that they 

 cannot be torn off; so they just 

 open their shells and breathe 

 in the refreshing salt foam, 

 which purifies their sluggish 

 blood and brings to their 

 mouths an abundance of food. 

 What care they for the howl of 

 the tempest or the dash of the 

 breakers? They have " built 

 their house upon a rock," and 

 the storm cannot harm them. Figure 27. 



