Shell-Bearers 



this each limpet constructs a little level patch on the rock 

 exactly corresponding to the size of its shell. And this, 

 again, brings us to a remarkable fact in the history of the 

 limpet. Inert as these creatures may appear at low tide, 

 they wander about over the surfaces of the rocks, when 

 they are covered with water, in search of food, returning 

 with unerring certainty to their particular level patch 

 after each foray. This homing instinct seems to be well 

 developed in the molluscs, for snails usually return to the 

 same place to roost evening after evening. With the 

 limpet its return is a case of necessity, for limpets are 

 of all sizes, so that individuals which cannot recognise 

 their own level patch and return to it are likely to 

 find a patch which does not fit them, with the result 

 that, to their undoing, they cannot adhere firmly to the 

 rock. 



Amongst land molluscs we can find few examples of 

 real ingenuity. The prickly snail is a little aeronaut and 

 becomes so in an ingenious manner. It is prone to ascend 

 trees, but loath to walk down again, so what does he do 

 but climb upon a leaf which is about to fall, takes a firm 

 hold and comes to earth on his primitive parachute. It is 

 fortunate that the snail only develops this tree-climbing 

 habit towards autumn, otherwise he would be com- 

 pelled to bestir himself and walk down any tree he had 

 ascended. 



The cuttle-fish and the sea-hare have respectively some- 

 what ingenious methods of escaping from their enemies. 

 When alarmed, instead of showing fight, or burying them- 

 selves in the sand or hiding behind seaweed or employing 

 any of the other methods usual to sea-dwellers, they simply 

 discharge a coloured fluid into the water and enveloped 

 therein they swim rapidly out of danger. 



We cannot close our chapter on molluscs without some 

 mention of pearls. Valuable as they are, when of good 

 quality, at the same time they are merely the result of 

 efforts on the part of the mollusc to prevent injury by a 



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