STRUCTURE OP THE LIMPET. 299 



means the case, for, like other molluscs, it migrates 

 from place to place. The tenacity with which it 

 adheres to the rock is worthy of notice. This feat 

 is performed on the same principle by which 

 various fishes, such as the lump, the remora or the 

 lamprey, are enabled to attach themselves to flat 

 surfaces, and by exactly the same process as that 

 by which the schoolboy's toy, called a leather- 

 sucker, is fixed to stones or other smooth surfaces. 

 The circular disk of the limpet's body or foot is 

 applied to the smooth surface of the rock, and by 

 means of the muscles, while the rim of the disk 

 is pressed down very closely, the centre is raised 

 up, thus creating a vacuum between the stone and 

 the animal's body ; the shell is therefore pressed 

 down upon the rock by the weight of the superin- 

 cumbent water and atmosphere, or if the tide be 

 out, by the weight of the atmosphere alone. Thus 

 a shell of which the mouth is but a square inch 

 in diameter, may be pressed down upon the rock 

 it adheres to with a weight of fifteen pounds, and 

 as the conical form of the shell is the most favour- 

 able for resisting the external force of the waves, 

 the limpet has the power of remaining unmoved 

 and in perfect safety in the most violent storms. 

 No candid and unprejudiced mind can avoid per- 

 ceiving how remarkable an illustration is thus 

 afforded of the doctrine of design and intention in 

 the structure of animals. The circular disk of the 

 limpet is constructed with express reference to the 

 laws of fluid pressure, as exhibited in the ocean and 

 in the atmosphere : the instinct of the creature 



