70 HABITS OP RAZOR-FISH. 



cated. But the tubular opening through which the 

 currents of water enter effectually protects the deli- 

 cate breathing-apparatus. Their strong muscular foot, 

 too, affords an instrument with which they can with 

 great rapidity dig into the sand, and thus escape pur- 

 suit. So rapidly is this mining operation performed, 

 that it requires some dexterity and quickness to surprise 

 even a Cockle in its hole, before it has burrowed beyond 

 our reach. But it is not as a digging-tool only that the 

 foot is employed; it is used in actual locomotion on 

 the surface, to enable the animal either to advance with 

 a crawling movement, or to make jumps along the sand. 

 The Common Cockle is not the least nimble of these 

 jumpers. It protrudes its foot to the utmost length, 

 bending it and fixing it strongly against the surface on 

 which it stands, and then, by a sudden muscular spring, 

 the animal throws itself into the air, and by repeating 

 the process again and again, it hops along at a rapid 

 pace. In the Cockle, which lives at no great depth in 

 the sand, the cohesion of the two membranes of the 

 mantle is not complete, and the tubes or siphons are 

 very short. In other genera, as the Razor-shells, which 

 burrow to a greater depth, the lateral cohesion is much 

 more perfect. The body of the animal is enclosed in 

 a sort of sac, while the tubes, through which currents 

 of water enter to the branchiee, are much protruded. 

 The animal can thus lie deeply ensconced in the sand 

 or mud, and keep the mouths of the tubes nearly on a 

 level with the sui-face of the sand, in direct communi- 

 cation with the water. 



The mode in which all the animals of this class feed 



