CARDIUM. 205 



can be projected considerably beyond the mouth of the 

 shell ; the fore part of this fleshy arm, when extended, 

 forms nearly a right angle with the mouth of the *hell, 

 and is the organ by means of which the animal executes 

 its confined progressive motions. 



Cockles generally bury themselves in the sand, near 

 the coasts, except the spiny species, which are capaci- 

 tated, by nature, to defend themselves from the attacks 

 of other marine animals, without having recourse to the 

 same precaution. Those which seek their safety in the 

 sand place themselves so, that the two tubes are turned 

 towards the surface, for the purpose of a ready commu- 

 nication with the water, whence they derive their nourish- 

 ment. But it is sometimes necessary for them to change 

 their situations, to leave their old apartments, or to bury 

 themselves in a new one ; and this is effected, according 

 to the observations of M. Reaumur, in the following 

 manner : When the animal wishes to sink into the sand, 

 it lengthens its fleshy arm, at the same time diminishing 

 its extremity, so that it becomes as it were pointed. 

 With this it makes a hole, and buries the arm in the sand, 

 continuing its mining operations with the pointed end ; 

 and by repeatedly lengthening and contracting this 

 muscular appendage, it in a short time works the shell 

 below the surface. When on the contrary the animal 

 would return to the light, it is only necessary to press its 

 lengthened arm, with firmness, against the sand, and the 

 shell will rise in proportion to the power exerted from 

 beneath ; by repeating this motion, the shell will soon 

 be disengaged, and the animal will effect its purpose. 

 By the same means the animal is enabled to move both 

 forwards and backwards, but in a verv limited degree. 



