THE MUSSEL AND ITS " BYSSUS." 287 



with a longitudinal furrow on either side. It is sub- 

 sidiary to a special gland ; the gland which, as we have 

 already said, secretes the tuft of silky threads known as 

 the "byssus." 



It is difficult to imagine what the mussel would do 

 without its byssus. It constitutes its special advantage 

 over the oyster; for while the latter is unable to accom- 

 plish any long or rapid journey, or any continuous 

 motion, the mussel is free to move about at all times and 

 in all directions. Attaching its byssus to some fixed 

 object, it draws upon it as upon a cable, and is gently 

 carried forward. But not only does the byssus act as a 

 locomotor, it is also an anchor, and when the animal is 

 moored by it to rock or pile, it defies the violence of the 

 strongest currents. Moreover, it can in this way suspend 

 itself to the face of a perpendicular crag, and keep its 

 shell to some extent above the surface of the water ; to 

 which cause the comparative smoothness of its shell is 

 probably owing. 



The mussel seems able to cling to any surface, however 

 slippery. Put one or two into your aquarium, reader, 

 and you will soon find them securely anchored to the 

 glass ; so securely, that to remove the shells you must 

 rend or sever the threads of the byssus, and these are 

 about a hundred and fifty in number ! It is a curious 

 fact that, to bind together the loose stones of the Cher- 

 bourg breakwater, the French sowed, or planted, tons of 

 mussels, thus depending on the tenacious and adherent 

 properties of the byssus. 



In almost all the seas of the world the mussel is to be 

 found, and on the English and Scotch coasts it is one of 

 the " common objects of the shore." It is used as an 



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