78 THE SEA-SIDE AND AQCTAKIUM. 



try a very simple experiment, by procuring from the 

 kitchen a piece of hearthstone which the servant, 

 by the way, observed was a very hard piece. With 

 some salt water to assist me, I rubbed the surface 

 with my finger, of course keeping to the same spot, 

 and in a very few minutes' time, I had made a very 

 sensible impression in the stone. I had not patience 

 to carry the experiment any further ; but as far as it 

 went, it left no doubt on my mind that with the foot 

 alone, without silicious particles, without a chemical 

 solvent, and without using the rasping powers of the 

 shell, our little animal could easily execute his self- 

 pronounced sentence of solitary confinement for life." 



With due deference to such an authority, I feel 

 confident in my own mind that Mr Sowerby, and 

 other writers who have also advocated this theory, 

 are totally mistaken, and that Mr Osier's theory is 

 nearer the truth, though it is not altogether correct. 

 I have had excellent opportunities of watching a 

 Pholas at work under singularly favourable circum- 

 stances, and I am enabled therefore to speak pretty 

 positively upon the question. 



In the general massacre of my Pholades by Blennies 

 and Crabs, I was left with only a solitary specimen, 

 seated, however, in a loose piece of rock ; the syphon 

 and upper portion of the shell being distinctly visible. 



To ascertain whether the Pholas moved in the 

 cavity, I used to place a pencil cross on the wooden 

 base of the Aquarium, and a corresponding mark 

 upon the white marbled baize beneath. To guard 



