FOOT OF RAZOR-SHELLS. 303 



enemy approaches, or to dig a furrow into which the animal 

 forces itself partially, and then advances slowly by making 

 slight see-saw or balancing motions, or even to jump along with 

 tolerable rapidity. Thus, the common Cockle protrudes its 

 foot to its utmost length, bending it and fixing it strongly 

 against the surface on which it stands ; then by a sudden 

 muscular spring it throws itself into the air, and, by repeating 

 the process again and again, hops along at a pace one would 

 hardly expect to meet with in a shell-bound mollusc. 



Even some of those which have but a very rudimentary foot, 

 incapable of subserving locomotion, are able to move from place 

 to place by the sudden opening or shutting of their valves. In 

 this manner the scallop, which inhabits deep places, where it 

 lies on a rocky or shelly bottom, swims or flies through the 

 water with great rapidity, and the file or rasp mussel, a closely 

 related genus, principally occurring in the Indian Ocean, glides 

 so swiftly through the water that the French naturalists Quoy 

 and Graimard were hardly able to overtake it. 



In the stone or wood-boring bivalves 

 the functions of the foot with regard to 

 locomotion are much more limited than 

 in the Cockle, or Tellina, as they merely 

 consist in moving the animal up and 

 down in the .cavity where it has. fixed its 

 residence. In the Eazor-Shells, which 

 will sometimes burrow to the depth of 

 two feet, and very rarely quit their holes, 

 the cylindrical foot, no longer fit for hori- 

 zontal locomotion, serves the animal for rising or sinking in the 

 sand, for when about to bore, it attenuates it into a point, and 

 afterwards contracts it into a rounded form so as to fix it by its 

 enlargement when it desires to rise. 



In places where the razor-shells abound, they are sought 

 after as bait for fish, and taken in spite of their mole-like 

 facility of concealment, for when the tide is low, their retreat is 

 easily recognised by the little jet of water they eject when 

 alarmed by the motion of the fishermen above. Having thus 

 detected their burrow, the wily enemy who is well aware that, 

 though inhabiting the salt water, the Solen does not like too 

 much of a good thing, merely throws some salt into the hole, 



