432 Mr STARK on Two Species of Pholas 



struum capable of performing that office." And, in another pas- 

 sage, he observes, " The Pholades are performing similar works 

 assigned by nature on softer substances, such as chalk, indurated 

 clay, and wood, which, in like manner, are perforated by some 

 solvent power : not by the thin fragile shells that cover such 

 animals, as some have erroneously asserted and is too generally 

 credited *." 



A late writer, Mr WOOD, supports something like the same 

 theory ; at least he seems to think that the attrition of the shell is 

 insufficient for the effect produced ; " since," says he, " there are 

 some species, and particularly the P. orientalis, which are nearly 

 smooth at the anterior end, and, consequently, unfit for such a 

 purpose f ;" while Mr GRAY, in the Zoological Journal, gives it 

 as his opinion, that the Pholades " appear to bore by means of 

 rasping J." 



Such are the discordant opinions that have been held regard- 

 ing the mode by which the Pholades perforate calcareous stones 

 and wood : one class of naturalists asserting that they do so by 

 the rotatory motion of their valves, or by means merely mecha- 

 nical ; while others suppose, from the apparent fragility of the 



* Testacea Britannica, p. 560, 561 . 



" It is well known (observes MONTAGU in another place) that animals as well as 

 vegetables prepare, by various occult processes, fluids powerfully corrosive : the viper 

 secretes a deadly poison, which is forced through the cavity of its fang ; the pismire, 

 and some other insects, eject a powerful acid, capable of dissolving calcareous stone. 

 Surely, then, it may most reasonably be admitted, that, by some such chemical means, 

 prepared in the great elaboratory of Nature, these testaceous Ascidia perform the part 

 assigned to them by the Creator of the Universe." MONTAGU, Supplement, p. 15. 



The Pholades, it is remarkable, bore the wood across the grain, while the Teredo 

 navalis perforates it in the direction of the fibres. 



f General Conchology, vol. i. p. 74. 



J Zoological Journal, No. 3. p. 406. 



