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 witb in a shell-bound molluse. 
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 Gaimard 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 Razor-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, 
