THE BORING MOLLUSCS. 83 



puted, the source of the animal's power is still an unsettled 

 question. 



How these bivalves bore their way has been a mystery, 

 mainly because zoologists have allowed themselves to be 

 thrown off their balance by contemplating the stupendous 

 results i^roduced by creatures so insignificant. But after 

 learning the history of the formation of coral reefs and 

 islands, we begin to appreciate the influence of minute 

 agencies continued through long spaces of time. The Teredo 

 and the Pholas have no powerful organs, but they have 

 patience ; and as far as I understand the matter, it is clear 

 that the disputes on this subject have been perplexed by the 

 desire to bring forward some organ so powerful as at once 

 to explain the animal's success in boring. Thus the latest 

 writer, M. Aucapitaine,* imagines he exjjlains the phenome- 

 non, by bringing forward the hypothesis of an acid secreted 

 by the animal, which corrodes the rock, or wood, and wliich 

 is then rasped away by a slow rotatory motion of the shell. 

 The boring is thus supposed to be a combination of chemical 

 and mechanical agencies. There is, however, one little diffi- 

 culty in accepting this explanation, which the author has 

 overlooked, as sj^eculators are wont to overlook fatal objec- 

 tions : the existence of this acid has yet to be proved ; its 

 presence is indispensable to the theory, but, unfortunately, 

 the fact of its presence is hypothetical. And when we have 

 got tangible hold of the acid, we must prove that, while it 

 has the property of attacking wood and rock, it has not the 

 property of attacking the calcareous shell of the animal. 



» Annales des Sciences Naturelles, 4'°°" serie, 1854 ; ii. 367. 



