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



absorption; and it remains to be proved whether they are 

 effected by a mere solvent or by mechanical means. 



The arguments before urged against the use of a solvent by the 

 boring Acephala are to a considerable extent applicable in this 

 case. It is impossible to conceive how it could be applied with- 

 out having its powers very much impaired by the diluting effect 

 of the surrounding element. When the mantle commences its 

 operations on the striated surface of Buccinum undatum, the ele- 

 vated ridges or striae are nearly obliterated before the grooves are 

 at all affected : the surface is therefore rapidly levelled. Were a 

 solvent used, the reverse of this might be expected to happen, for 

 the fluid accumulating in the depressed lines would act there 

 more vigorously than on the elevated parts, and the consequence 

 would be the exaggeration of the grooves. Holes and cracks cut 

 over are not enlarged, as every one conversant with etching is 

 aware they should be were a solvent fluid used. As before re- 

 marked, extraneous obstructions of a calcareous nature can be 

 removed : the sandy sheath however of Terebella lumbricalis re- 

 sists the power of the mantle. When this animal retards the 

 growth of the mollusk, it is covered over by the inner lip, and 

 distortion frequently arises in consequence. The sand attached 

 by this species of Terebella is composed almost entirely of rather 

 large siliceous particles ; and from what we know respecting the 

 boring of the Acephala, it might be inferred that the sheath of 

 this animal could not be removed. The question is not mate- 

 rially affected, on either side, by this fact, though if a solvent be 

 the agent, it must have the power, one would think, of removing 

 in the first instance the epidermis ; and if so, there does not ap- 

 pear any good reason why the corroding fluid should not find its 

 way to the horny sheath that holds together the siliceous par- 

 ticles, and reducing it liberate the sand. The improbability of 

 the use of an acid solvent is increased by the fact that it must 

 be supplied by the same organ that secretes the calcareous matter 

 forming the inner lip : certainly this may be supposed to come 

 from the mantle further back, and the solvent from the extreme 

 edge of it ; but this does not remove the difficulty, for the one 

 would still be liable to interfere with the other. 



The action of currents is apparently out of the question in this 

 case, as the mantle is furnished with cilia only on the surface 

 next the animal ; on that next the shell I could detect none : it 

 is supplied, however, with crystalline bodies similar to those be- 

 fore described in the foot and mantle of the boring mollusks. 

 Then, shall we not conclude that it is by their agency that the 

 columella is reduced, and that spines and other obstructions are 

 removed from it ? Analogy would lead to this conclusion, assu- 

 ming that we have arrived at a correct view respecting the boring 



