270 Mr Osier on Burrowing and Boring 



Art. XXI. — On Burrowing and Boring Marine Animals 

 By Edward Osler, Esq. * 



The object of Mr Osier is to explain the mechanism by which 

 the boring and burrowing shell-fish form their habitations. 

 With regard to the Pholades, about whose mode of boring the 

 softer rocks and wood much difference of opinion has prevail- 

 ed among naturalists, Mr Osier coincides entirely with Mr 

 Stark f in thinking that they perforate their habitations by me- 

 chanical action alone. From the anatomical structure of the ani- 

 mal of the Pholas Candida, and the actual observation of its 

 young by this gentleman, this fact seems now placed beyond the 

 possibility of doubt. 



The Pholas, says he, has two methods of boring. In the 

 first it fixes itself by the foot, and raises itself almost perpen- 

 dicularly, thus pressing the operative part of the shell upon 

 the substance to which it adheres ; it now proceeds to execute 

 a succession of partial rotatory motions, effected by the alter- 

 nate contraction of the lateral muscles, employing one valve 

 only by turning on its side, and immediately regaining the erect 

 position. This method is almost exclusively employed by the 

 young ones. When above two or three lines in length, the alter- 

 ed figure of the shell, and the increased weight of that part 

 of the animal behind the hinge prevents it from raising itself 

 perpendicularly, independent of the narrow space it now oc- 

 cupies. Attached by the foot, the lateral muscles contract, 

 and, raising the posterior extremity of the shell, press its ope- 

 rative part against the bottom of the hole ; and the moment 

 after, the action of the posterior adductor brings the dorsal mar- 

 gins of the valves into contact, so that the strong rasp-like 

 portions are suddenly separated, and scrape rapidly and for- 

 cibly over the substance on which they press. 



Every peculiarity of structure upon which the boring powers 

 of the Pholas depends, exists in an equally marked degree in 

 the Teredo navalis, which, happily for the shipping of this 

 country, Mr Osier states to be nearly and probably quite ex- 



* Mr Osier's paper is printed in the Philosophical Transactions for 

 1826, part iii. p. 342. 



T See this Journal, vol. v. p. 98, and Edinburgh Transactions, vol. x. 

 part ii. ' 



11 



