PHOLAS. 105 



the animals have the power of secreting different acids at 

 will, according to the substance they have to attack. Yet 

 this notion has been most favoured by naturalists, who, 

 sceptical as to the perforating power of such fragile instru- 

 ments as are the shells of many of these creatures, endowed 

 the animals with supernatural chemical qualifications. 

 Even good experimental observers, — Mr. Osier for one, — 

 whilst they proved that the Pholas could bore mechanically 

 by the rotation of its valves, could not free their minds 

 from the prejudice in favour of a solvent. The important 

 statement put forward by Mr. Albany Hancock respecting 

 the instruments by which mollusca bore, and which, so 

 far as Gasteropoda are concerned, appear to furnish us 

 with a true explanation, namely, that it was eftected 

 by means of siliceous particles, variously arranged in 

 certain portions of the animal's body, led us to hope 

 that a better cause than any yet alleged had been dis- 

 covered. But we cannot bear it out with respect to the 

 PJioladidee. We can find no such particles in the man- 

 tle of Teredo, nor have any been noticed by Home or 

 Deshayes, or by the most recent observers, Frey and 

 Leuckart, who paid especial attention to the structure of 

 the tissues in this genus. Nor could we, although aided 

 by the anatomical and microscopical skill of Mr. Busk, 

 detect any siliceous particles in either the mantle, foot, or 

 siphon tube of Pholas Candida. If present in any species, 

 therefore, they are exceptional, so far as the genus Pholas and 

 its allies are concerned. The shells of several British species 

 of Pholas, and that of Pholadldea, have been chemically 

 examined by our friend, Mr. Trenham Reeks, with a nega- 

 tive result as regards the presence of particles of silex in 

 their substance, where, after the statement of Mr. Hancock 

 respecting the structure of the mantle, we thought they 



VOL. I. p 



