288 Scientific Intelligence. 



III. Zoology, 



On the Boring of Mollusca into Rocks and on the removal of 

 Portions of their Shells ; by Mr. A. Hancock, (Proc. Brit. Assoc, 

 Athen., No. 1086.) — The author stated that three theories had been 

 advocated as to the way in which the mollusks effect their entrance in- 

 to the rocks, &c, in which they are found. The first is, that the ani- 

 mal works with the shell in the manner of a rasp or an auger. The 

 second, that it secretes an acid whereby the substance with which it 

 comes in contact is dissolved. The third, that the effect is produced 

 by the vibratile action of the parts exciting constant currents of water 

 against the substance, aided by its impetus when drawn in down the 

 elongated body of the animal. The author objected to all these theo- 

 ries. In opposition to the first, he stated that the burrows are tortuous 

 and of a form to render it impossible that the valves of the shells 

 should act as a centre-bit or auger. Again, the spines that cover 

 many of the shells are covered with an epidermis which, if the shells 

 were used for boring, would be rubbed off — which is not the case. 

 The young of these creatures commence boring directly they are 

 hatched, when their shells are too delicate to produce any effect on the 

 substances into which they penetrate. In opposition to the theory that 

 a solvent is employed, the author stated that this must be of an acid 

 nature, and that by the most careful experiments he had been unable 

 to detect the slightest indication of any acid secretions from any part 

 of the bodies of these animals. Besides, if a solvent were secreted 

 capable of dissolving calcareous and sandstone rocks, ought it not also 

 to act on the shell of the animal ? — which was found not to be the 

 case. The physical appearances of the excavation, also, were not 

 like those produced by a solvent. It would not account, either, for 

 their boring in wood. The wood found in the stomach of the Teredo 

 navalis was found to be chemically unchanged. The theory of the 

 ciliary currents was objected to on the ground that it was inadequate to 

 explain the phenomena. If these delicate ciliary currents were capa- 

 ble of effecting this object, the dashing of the water over the same sur- 

 faces ought to have as much more effect as their physical force is 

 greater. The anatomical structure of the part, also, on which the cilia 

 are situated would forbid the supposition that currents produced by them 

 could effect this object. These theories being insufficient to explain 

 the phenomenon, the author proposed a new one. He believes that the 

 anterior portion of the animal is the excavating instrument. This, in 



Teredo and Pholas, is composed of the foot and edges of the mantle 

 which together fill up the frontal gape of the shell. In Saxicava and 

 Gastrocluvna it is formed wholly of the edges of the mantle, which 

 are united and thickened. The form of the excavation corresponds to 

 the form of these organs. On a minute examination of the surface of 

 the foot of Teredo Norwegica it is found, under the microscope, to be 

 crowded with minute brilliant points, which on being compressed, con- 

 sist of comparatively large crystalline bodies embedded within them. 

 These crystals are numerous and of various sizes and shapes, chiefly » ve 

 and six-sided, but not by any means regularly so. They all agree in hav- 





