THE SHORES OF BRITAIN. 105 



each shell. Instead of a collar, each leaf of the mantle 

 is here fringed with a series of delicate fleshy threads, 

 which secrete the exterior part of the shell, by being 

 thrust out round the edge ; while the whole surface 

 of the mantle deposits the beautiful, rainbow-tinted, 

 pearly substance with which the interior is coated. 



Instead of the fleshy belly on which the Univalves 

 glide along, the Bivalves are furnished with a pecu- 

 liar organ, which in some species serves the purpose 

 of motion. The Oyster, however, and some other 

 species, have no power of changing their position, 

 but are, as it were, cemented to the rock on which 

 the spawn first chanced to fall. The Mussel, again, 

 is fastened, but in a different manner, being moored 

 by a cable of silken threads, which it spins from its 

 own body. But the Cockle, which is eaten by the 

 poor on many of our shores, is enabled to move with 

 considerable rapidity by means of the organ to which 

 I have just alluded. It is somewhat like a tongue, 

 and can assume a great variety of shapes. The 

 Cockle burrows in the mud : having lengthened and 

 stiffened its tongue or foot, it pushes it as far as it 

 can reach into the mud ; then bending the tip into a 

 hook, it forcibly contracts it, and thus brings its 

 body, shell and all, into the hole. The Razor-shell, 

 a shell common on sandy beaches, of a long narrow 

 form, has this power still more remarkably deve- 

 loped. 



Many of the islands which stud the sea around the 

 north and west coasts of Scotland are remarkable for 

 the stern grandeur of their precipitous cliffs. One 

 might almost imagine that the surges of the mighty 



