found on the Sea-coast near Edinburgh. 435 



instances where it is next to impossible that, without the aid of 

 a solvent fluid, such animals could form protecting cells in hard 

 substances. From not having seen the animals alluded to alive, 

 and in their native habitations, it would be presumption in me 

 to give a decided opinion on the subject. But, reasoning from 

 analogy in the structure of the animals, and the habits of such 

 as have been observed, it infers no impossibility to conceive that 

 they penetrate rocks in a similar manner. Little asperity in the 

 instrument is required where the operation is constant. In judg- 

 ing of the unseen or unobserved operations of nature, many are 

 guided in their opinion by what appears possible to be effected 

 by the limited powers which a preconceived theory prescribes 

 to the instrument employed. But little is known regarding 

 the time which these instinctive miners take to form their 

 deepening cells. A drop of water falling constantly on the 

 same spot soon leaves evidences of what time, with the smallest 

 force, can effect ; and the keys of musical instruments are, in no 

 long period, hollowed by the softest touch of the softest fingers. 

 There seems no impossibility, therefore, in conceiving that the 

 Pholades may perforate a substance less hard than their own 

 shell by mere attrition *, or even a harder substance, by the con- 

 stant action of their muscular foot. 



LINNAEUS and LAMAKCK regard the Pholasas a Bivalve shell, 

 with accessory pieces ; while others, from the presence of these 

 auxiliary plates, have classed it among the Multivalves. The 

 animal is hermaphrodite and viviparous, hatching its young in 

 the little sacs of its branchiae. It has a membranous mantle, of 



* Of the power of the Pholades to bore limestone, marble, or shale, it is easy to 

 satisfy one's self, by the simple experiment of rubbing the shell gently on a piece of 

 marble, which it cuts without rounding the asperities of the shell. Oak is likewise 

 scratched in the same manner ; but the action of the Pholades is always on submerged 

 wood or rocks partially covered by the tide, and the water, in both cases, must facili- 

 tate the process of boring. 



3 



