MOLLUSCA ACEPHALA. '201 



sand. Mr. Osier, who has given us this account,* 

 observes that the instinct, which directs the animal 

 thus to procure a shelter, operates at the earliest 

 period of its existence. The Mya truncata^ when 

 fully grown, will not attempt to burrow ; but on 

 placing two young ones, which were scarcely more 

 than a line in length, and apparently but just ex- 

 cluded, on sand, in a glass of sea-water, he found 

 that they buried themselves immediately. 



By a process exactly the inverse of this, that is, 

 by doubling up the foot, and pushing with it down- 

 wards against the sand below, the shell may be 

 again made to rise by the same kind of efforts 

 which before protruded the foot. By this process 

 of burrowing the animal is enabled quickly to 

 retreat when danger presses : and when this is past, 

 it can, with equal facility, emerge from its hiding- 

 place. 



The Cardlum can also advance at the bottom of 

 the sea along the surface of the soft earth, pressing 

 backwards with its foot, as a boatman impels his 

 boat onwards, by pushing with his pole against the 

 ground in a contrary direction. It is likewise by 

 a similar expedient that the Solcu forces its way 

 through the sand, expanding the end of its foot 

 into the form of a club. The course of these 

 locomotive bivalves may readily be traced on the 

 sand by the furrows which they plough up in their 

 progress. 



These, as well as many other of the bivalve 

 mollusca, are enabled by the great size and flexi- 

 bility of this organ to execute various other move- 



* Philos. Trcuis. foi 1826, p. 349. 



