Burr owing and'Statianary Mollnsca, 



355 



The holes are to the depth of 4 in. ; and it is observed that 

 the nodules of quartz and feldspar, which sometimes occur in 

 the hard limestone of the pillars, are untouched.* In what 

 manner this temple was submerged and again left dry has 

 much puzzled and perplexed philosophers, and the discussion 

 is fortunately beyond our province ; but it becomes us to 

 enquire by what means shell -fish make these holes, for which, 

 apparently, they are most unfit. 



The point has been much debated, and it seemed so hard 

 to solve, that Rondeletius saw nothing for it but to suppose 

 that the sea water, lodging in the rocks, was itself transformed 

 into Pholades and other saxicavous Mollusca ; and other phi- 

 losophers, as Mr. Bingley good-naturedly calls them, were 

 driven to the belief that they entered the rock while it was yet 

 in a soft state, which afterwards hardened by degrees around 

 them. Two explanations of the process have divided less 

 imaginative naturalists : the one is, that the creatures bore by 

 the aid of a solvent liquor which they excrete ; the other, 

 that they do so by the friction made by semi-rotatory motions 

 of the shell. I will not detain you with a regular defence of 

 either opinion; for it is very probable that neither is applicable 



to all of these Mollusca, some of which 

 are certainly mechanical borers, while 

 others apparently operate by a che- 

 mical menstruum. This is the view 

 which. Mr. Osier has taken of the 

 subject, in a paper of very great ex- 

 tent, from which I shall give you 

 some rather long extracts, the more 

 willingly, as it is contained in a 

 work not easily accessible in remote 

 situations, f 



The anatomical structure of the 

 Pholas leads to the conclusion that 

 it excavates its cell mechanically, b^ 

 employing the shell as a rasp; and 

 the part which it employs ia ijoring 

 is the anterior and lower portion of 

 phMas Candida. «, The ligament ^^^ shcll, which is thicker and armed 

 and process to which it is attached, ^jth much strouffer spiucs than auv 



*, The lateral process, c, The pos. ■\it r\ -i t - 



terior adductor, d. The anterior other part. Mr. Uslcr haS fflVCn a 



adductor, e. The accessory valves . , . r t t • • r 



over the hinge. mmute accouut ot the peculiarities oi 



* Brewster's Journ. of Science for Oct. 1829, p. 271. 



f Phil. Trans, for 1826, part iii. " On Burrowing and Boring Marine 

 Animals." By Edward Osier, Esq., p. 342. What follows of this letter is 

 almost entirely taken from this admirable paper. 



A A 2 



