Zoology. 289 



ing one or more elevated points near the center. These bodies are 



highly refractive, and are for the most part pretty regularly distributed 

 over the whole convex surface of the foot, but are occasionally congre- 

 gated into masses. Similar crystalline bodies are embedded in the 

 edges of the mantie surrounding the foot. In Pholas the same appear- 

 ance is presented both in the foot and the surrounding edges of the 

 mantle. Saxicava rugosa has also the anterior portion of the animal 

 abundantly provided with crystalline bodies like those already descri- 

 bed ; so also with the foot and mantle of Patella vulgata. These 

 bodies are constantly being shed. Acetic acid has no effect on them ; 

 and in Saxicava, strong nitric acid produces no change after several 

 days' immersion. Those of Pholas and Teredo appear to be ultimate- 

 ly acted on by this acid, but are never totally destroyed by it. It is 

 by means of these bodies that the author believes the animal rasps 

 down the substances in which they are found. The whole of these an- 

 imals are also supplied with powerful muscles by which they may effect 

 the necessary movement for the production of this result. Judging 

 from analogy, the author believes that all the boring mollusks excavate 

 in the same manner ; none by the rasping or cutting of their valves, 

 none by a solvent, none by ciliary currents. In the same manner he 

 accounts for the gradual disappearance of certain portions of the colu- 

 mella in the gasteropodous Mollusca; not by the process of "absorp- 

 tion," as has been supposed. 



Mr. Phillips explained more fully the nature of the boring process 

 carried on by these animals, and thought the author of this paper had 

 thrown much light on the subject. Granules on the tongue of many of 

 the Mollusca had been long known. They appeared to be of a siliceous 

 character. — Prof. Owen stated that there was no a priori objection to 

 the theories opposed by the author, and one or another had been adopt- 

 ed by naturalists to explain the phenomenon of boring. At the same 

 time, the inadequacy of these theories for the explanation of some 

 cases had led him to regard the foot and mantle as engaged in the ope- 

 ration, — how, he now, for the first time, was informed. He still, how- 

 ever, thought that an exception ought to be made in the case of Pholas 

 navalis, which he yet believed must burrow in wood by means of its 

 she!l._p ro f. E t Forbes said that having to write on this subject in his 

 History of the British Mollusca, 11 he had carefully gone over the evi- 

 dence in favor of all the views adopted, and was not unaware of those 

 °f the author. He found little evidence to support the theory of a sol- 

 vent being employed, or of the agency of ciliary currents; but he found 

 a s little in favor of the siliceous particles of the author. He had care- 

 fully examined Saxicava, and could find no siliceous granules. Mr. 

 Heofrey had examined these creatures under the microscope, and had 

 foiled to detect anything of the kind. A chemical examination made 

 b y Mr. Henry had also failed to detect them. He did not deny that 

 they might be present in Clavagella. Under these circumstances, he 

 had endeavored to take an eclectic view of the subject. The different 

 substances into which these animals penetrated might require different 

 means. Some species of the genus Pholas bored in wood, some in 

 stone, but none in both. — Mr. Hancock had referred to a species of 

 sponge, the Clione, as a borer. This animal was undoubtedly irritable, 



Second Series, Vol. VII, No. 20.— March, 1849. 37 



