How Animals Work. 



a 'hook and so fixing it firmly in the ground, it drags 

 itself, shell and all, beneath the surface. Not only as 

 a spade to dig an underground domicile, however, 

 does the Cockle use its powerful foot, for when on the 

 surface of the sand the little Mollusc can progress 

 towards the incoming tide by a series of leaps and 

 bounds, by pressing its foot firmly against the ground, 

 bending it, and then letting it go so that it acts as a 

 spring. 



One of the most interesting of the mining Molluscs 

 is the Solen, or Razor-shell, which excavates a vertical 

 tunnel in the sand in which to live, quite low down 

 on the shore, so that the entrance to its burrow is only 

 exposed at low spring tides. Again, as in the cockle, 

 it is the powerful foot which the Solen employs in dig- 

 ging its vertical retreat, and the process is a very in- 

 teresting one to watch. Suppose the Solen to be 

 resting on the surface of the wet sand, the animal will 

 cautiously push out its foot from the safe shelter of 

 the long razor-case-like valves of its shell, and feel about 

 for a soft spot ; then the pointed tip of the foot is 

 thrust into the sand, the prone shell is pulled into an 

 upright position, and gradually, by a series of jerks, 

 disappears from view, an oval keyhole-shaped opening 

 on the surface of the sand marking the entrance to 

 the vertical burrow. The way in which the Solen 

 uses its foot to drag itself down the shaft is really very 

 remarkable. When first pushed into the sand the 

 foot is flat and sharply pointed at its tip, so that it slips 

 easily into the soft moist sand. Then, when it has 

 been forced down as far as it will reach, the animal 

 curves up its toe to form a sort of hook with which it 



40 



