232 Mr. A. Hancock on the Boring of the Mollusca into Rocks, 



they all burrow in a soft sandy material cemented by lime. But 

 all these species are stated by Montagu to occur in wood. On 

 the coast of Northumberland, P. Candida and P. crispata, as be- 

 fore mentioned, burrow in shale ; the latter occasionally in shaly 

 sandstone ; and Mr. Hogg has found these two species in wood 

 at Seaton. There can be little doubt, however, that all the 

 Pholades penetrate by the same means ; and as P. striata bores 

 into the hardest oak, it is evident that its excavating powers are 

 equal to those of Teredo : and from the close alliance of the two, 

 it is but fair to assume that the instrument is the same in both. 

 Now, since the discovery of excessively fine sawdust in the body 

 of Teredo, we cannot deny that it bores mechanically; and must 

 therefore conclude that Pholas does the same, or at least, that 

 such is probable. 



Some, indeed, have doubted the nature of the impalpable saw- 

 dust found by Sir Everard Home in the interior of Teredo ; but 

 having had the opportunity of examining a great number of spe- 

 cimens, I feel perfectly satisfied of his accuracy, and also of that 

 of Mr. Hatchett, who had this substance submitted to him, and 

 found it unaltered by the action of the stomach or otherwise 

 chemically changed. In many instances I have taken the re- 

 duced wood from the half-decayed and dried-up bodies of these 

 animals : it fills nearly one-third of the worn-like portion of the 

 creature. In a piece of deal in my possession, well filled with 

 Teredo, every individual contains more or less of this microscopic 

 sawdust, which is of a pale yellow colour of the same tint as the 

 wood, and when moist is soft and pulpy : it readily separates in 

 water, and exhibits a granular appearance : when dry it burns 

 freely with a flame, chars, and emits a smell exactly like that of 

 burnt wood. I have also taken this comminuted wood out of 

 animals buried in mahogany : in this case the sawdust is a dark 

 obscure red resembling the colour of the wood. Sir Everard 

 is not inclined to believe that the animal derives any nourish- 

 ment from the wood, and, indeed, its unaltered state goes far to 

 prove that it does not. The passage of the reduced wood through 

 the body of the animal would appear to be necessitated by the 

 great length and tortuous direction of the bore, which we have 

 already seen is entirely filled up by the Teredo. The partial 

 attachment of the siphonal extremity to the calcareous sheath 

 would also tend to prevent an exit in the usual way. 



The theory of Mr. Garner, that the currents of water produced 

 by the vibratile cilia of the animal are sufficient to work out the 

 excavations, appears to be very unsatisfactory, and quite inade- 

 quate to explain the phenomena attending this interesting 

 subject. 



In the first place it must be borne in mind, that the burrows 



