212 SHELLS AND MOLLUSCOUS ANIMALS. 



embedded in a cavity which it makes, of exactly 

 the size and form fitted to hold its shell. So firmly 

 can it attach itself, that if by any movement of 

 the hand we allow the animal to guess at our 



intention of taking it, it becomes almost impossible 

 to tear it away, unless by putting the blade of a 

 knife between it and the stone. The power of 

 holding itself thus is owing to the great number 

 and strength of the fibres of its foot, which, by 

 raising the middle part, form a hollow in the 

 centre and act as a sucker. This means of 

 adhesion protects the limpet not only from the 

 violence of the waves, but also from the strength 

 or skill of the numerous birds and animals which 

 relish it as food. There are many species of limpet, 

 but even the practical conchologist finds some 

 difficulty in distinguishing them from each other, 

 on account of the power which the animal has of 

 altering its shell to suit its circumstances, adapting 

 the rim to the shape of the substance on which it 

 is found. Thus, when a limpet makes a dwelling- 

 place on the leaf of a large sea-weed or on a flat 



