84 THE SEA -SIDE AND AQUAKIUM. 



substance always seemed scraped on the surface. I 

 cannot, therefore, but believe that the ligament aids 

 very materially in rubbing off the rock, or, at all 

 events, in graduating the pressure of the valves dur- 

 ing the same process, and that this curious formation, 

 instead of being worn away, may, like the callosity 

 upon a workman's hand, increase in toughness the 

 more labour it is called upon to perform. Still I 

 feel pretty confident, that although the ligament 

 may greatly assist, the shell, as I have said before, 

 forms the principal agent in boring the animal's 

 dwelling. 



The conclusion I arrive at from these facts, may 

 be thus summed up : That as the Pholas only bores 

 the rock in sufficient degree to admit of its increased 

 bulk of body, it only requires to bore occasionally; 

 that there may be often an interval of many months, 

 during which time nature will have renewed the 

 serrated edges and rough surface of the valves, and 

 thus enabled the creature to renew its wondrous 

 operations. 



The probability of the correctness of this idea is 

 further confirmed by the fact, that the Pholades are 

 generally found not very far beneath the surface of 

 the rock in which they live. My specimen, too, did 

 not attempt to bore for a period of two months. 

 How long it had been passive hitherto, is known only 

 to Him who watches lovingly alike over this poor 

 bivalve, as over the most exalted of His creatures. 



There is a most singular circumstance, which I 



