and Limnoria terebrans. 125 



it can only be effected by means of a solvent. I am not inclined 

 to adopt either theory, but venture to advance what I believe to 

 be a new view of the subject. I would ascribe the smoothly 

 rounded termination of the cell to the action of a solvent* ap- 

 plied by the proboscis (so called by Sir E. Home, who mentions 

 its vermicular motion, though he attributes to it a very different 

 use), which thus acts as a pioneer in mining a passage, that is 

 afterwards increased to its final dimensions by the boring action 

 of the primary valves. The spherical termination, I am satis- 

 fied, could not be effected by these valves or boring shells, al- 

 though, with the exception of this smoothly rounded part, they 

 afford sufficient evidence of their rasure in the irregular trans- 

 verse furrows which are more or less apparent throughout the 

 entire circumference of the cell. With regard to Montagu's ar- 

 gument of the constant presence of an epidermis on the boring 

 shells, the only part of the shell that I conceive to be requisite 

 for the operation of cutting, is, in the specimens which have 

 come under my observation, always free from such a covering, 

 and so far from being " tender and fragile," is abundantly strong 

 and sharp for the purpose here allotted to it. 



During the nine or ten years that the Teredo has been esta- 

 blished at Portpatrick,-f- it has not degenerated, as specimens 



cate, which must be the case if it were effected on the principle of a centre 

 bit." That of Colonel Montagu is, that " live shells are always covered with 

 an epidermis, which must eventually have been removed by the necessary 

 friction applied to the boring and piling of timber." 



• Not having a knowledge of chemistry, I cannot pretend to say what this 

 solvent may be. The most recent suggestions I am aware of on the subject 

 of solvents is the following, which I extract from the last work of my friend 

 Dr Drummond, entitled " Letters to a Young Naturalist." At p. 266 of the 

 first edition of this work, it is asked relative to the power possessed by the 

 Pholades of boring, " May it not be possible that the animal has a power of 

 decomposing the sea-salt as its wants may require, and applying the liberated 

 muriatic acid to the solution of the calcareous rock ? The muriate of lime is 

 particularly soluble in water, so much so, indeed, that it forms a deliquescent 

 salt, and therefore it would be carried oft' as fast as it could be formed. This, 

 however, is mere conjecture; but the subject is worthy of regular investiga- 

 tion by observation and'experiment." 



f This space of time is presumed from a comparison of the effects of the 

 Teredo in the first piles in which it was noticed about five years since, with 

 those now taken up, which are known to have been put under water at that 

 period. 



