102 PIIOLADIDtE. 



M. Deshayes, in his splendid work upon tlie mollusca of 

 Algeria, maintains that the Teredo bores by means of a 

 solvent. The foot (which, however, he regards not as 

 such, but as a special secreting organ) presents a circular 

 smooth surface surrounded by a thick fleshy ring, so as to 

 constitute a sucker, by means of which the animal attaches 

 itself to the wood, and denudes the anterior extremity of the 

 gallery it inhabits. He believes that the contact long pro- 

 longed of this part of the animal with the wood, macerates 

 and renders it friable, by the action of a special secretion, of 

 which the product impregnates the leaflets of the fleshy ring, 

 and does not diffuse itself, or become dissolved in water. 



M. F. Oaillaud'" holds a similar opinion with respect to 

 the perforating power of animals of the genus Clavagella, 

 which he maintains perforate by a solvent acid. This acid 

 he supposes to be developed in very small quantities at a 

 time, for otherwise the shell itself would be attacked by it. 

 He believes the animal has the j)ower of ajjplying the acid 

 to the point where it wishes to work, and that it can dilute 

 the solvent with water in case it threatens to endanger the 

 shell. 



In the " Annales des Sciences Naturelles" for 1839, 

 M. L. A. Necker published some very interesting and im- 

 portant observations on the mineralogical nature of the 

 shells of mollusca, in which he points out difterences of 

 structure as indicated by polarization of light. In it he 

 has the following observations on the subject in question : 

 " It is very remarkable that two genera of perforating 

 shells, the Pholas and the Venerupis, radiate strongly calc- 

 spar. Thus the asperities which roughen their shells may 

 with the aid of the acids with which they are provided, 

 excavate the calcareous rocks inhabited by them. The 



* Mag. deZoolugiu, 1842. 



