Z ^'' EDI3LE BRITISH MOLLUSCA. 



solid oak a material ten times harder than itself. He 

 also observed that the form of the tube is evidently 

 not the result of an auger-like instrument, because it 

 is broader at the bottom than at the top and sides. 



Dr. J. G. Jeffreys, who quotes the above in his 

 ' British Conchology/ agrees with Sellius that the foot 

 or muscular disk, and not the shell, is ' ' the sole instru- 

 ment of perforation by the mollusca of stone, wood, 

 and other substances, which is closely applied to the 

 concave end of the hole, and is constantly supplied 

 with moisture through the glandular tissues of the 

 body." He adds, " By this simple, yet gradual process, 

 the fibres of wood or grains of sand-stone may easily 

 be detached or disintegrated, time and patience being 

 allowed for the operation." Some naturalists believe 

 that it is accomplished by means of an acid contained 

 in the fish, by which it dissolves the calcareous rocks ; 

 while others maintain that the Pholas bores by using 

 its shell as a rasp. This mechanical process is fully 

 described by " Astur/' who, from his own observa- 

 tions, has endeavoured to solve the problem, and who, 

 to quote the late Mr. Buckland's words, is apparently 

 the only person " who has ever seen the Pholas at work." 

 In the ' Field/ " Astur " published some time since an 

 interesting description of the method by which this 

 mollusk bores its habitation. He says, " Having pro- 

 cured several of these mollusks in pieces of timber, I 

 extracted one, and placed it loose in my aquarium, in 

 the vague hope that it would perforate some sand- 

 stone on which I placed it. It possessed the powers 

 of locomotion, but made no attempt to bore. I then 

 cut a piece of wood from the timber in which it had 

 been found, and placed the Pholas in a hole a little 



