THE ANIMAL KINGDOM. 81 



clothes. This is not due to their being really of this colour, 

 but to a cement formed by the splashes from the rocks, 

 which cover the bodies of this peculiar class of men, and 

 which issue as they cleave the rocks with powerful blows 

 of the pickaxe, in order to find in their depths the molluscs, 

 which they sell to the fishermen. 



When, after overcoming the obstacles presented by a 

 rocky and slippery ground, we reach the neighbourhood 

 of the laborious workman, and, having induced him to 

 pause from his work in order that one may keep clear of 

 the amj)le circle of splashes radiating from his hatchet, we 

 examine the pholads lying here and there among the broken 

 stones, we return quite convinced that there exist shell- 

 fish which gnaw stone — a fact which many people doubted 

 not long ago. But another problem remains to be solved, 

 and that is to know how these animals execute a task 

 which seems so much beyond their powers. 



Some naturalists have fancied that the Pholades ai'e 

 only a kind of living files, mechanically boring their habi- 

 tations by rasping the rock with the aid of the sharp points 

 on their shells. But this opinion is C[uite untenable, for 

 before they could pierce the hard stone these delicate pro- 

 jections themselves would be completely worn away. 



Other naturalists think these molluscs make use of 

 some chemical process, and hollow out their abodes by 

 distilling an acid which acts upon the stone. This theory 

 is not more admissible than the other, for it is certain 

 that, the calcareous outer skeleton of the animal being of 

 a composition analogous to that of the rock, it would itself 

 be the first victim of the corroding agent, and would be 

 dissolved long before the hole was formed.^ 



^ The opinion that the erosion of rocks is effected by the friction of the shell 

 within it cannot be sustained ; not only because the finest points would be worn 



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