USES OF THE " FOOT." 483 



process, the creature manages to bury itself with a 

 rapidity that is quite astonishing. 



The manner in which it reascends towards the sur- 

 face is precisely the reverse of the preceding opera- 

 tion : the foot becomes dilated into a bulb, close 

 beneath the inferior end of the shell, and there, 

 taking a firm hold of the surrounding sand, the Solen 

 is enabled, by forcibly elongating the organ, to push 

 itself upwards. 



These movements of the foot may be readily wit- 

 nessed when the Razor-shell has been dug up from its 

 hiding-place, particularly that whereby it is enabled 

 to bury itself in the sand ; for, if held up in the 

 fingers, it thrusts out its leg, and performs all the 

 necessary evolutions, whilst making fruitless attempts 

 to save itself after its usual plan of escape. 



Other species of bivalves, when inclined for a walk, 

 leisurely protrude this remarkable locomotive organ, 

 and, extending it to the utmost, apply it cautiously 

 to some solid support, and then, by contracting it, as 

 with a painful effort, pull themselves along ; the foot 

 is now again extended in the same cautious manner, 

 and the shell again dragged forward to the point of 

 fixture. Reaumur has happily compared this mode 

 of progression to that of a man, who, having laid 

 himself flat on the ground, attempts to move onward 

 by the sole aid of one arm ; he stretches the arm out, 

 to take hold of some object which he can just reach, 

 and thus drags himself along : the difference between 

 the action of the foot of the bivalve, and that of the 

 arm, consisting only in the circumstance that, in the 

 former, the shortening is effected by a general con- 



Y2 



