PHOLAS MUSSEL COCKLE. 83 



passive state, or when its foot is through the aper- 

 ture, no such threads are ever to be seen. 



I am better able to state, from my own observa- 

 tion, that there can be no doubt it is with the shell, 

 and not with any acid or flinty particles, that the 

 creature bores the rock. 



Professor Forbes held that if this were the case, 

 the rasping points on the surface of the valves would 

 soon be worn clown an appearance which, he says, 

 never is seen. With due respect to such a name, I am 

 convinced he was in error. Not only are the edges 

 worn, but the rough surface is worn nearly smooth, 

 appearing in certain parts of a shelly white colour, 

 instead of a light drab, as my specimen proves. 



But the reader may ask, If certain parts of the 

 valves are worn nearly smooth, and the animal worked 

 so vigorously, how is it they were not rasped through ? 

 This is a very natural question, and one that I put 

 to myself repeatedly. 



I have made frequent and careful observations 

 with a powerful lens, while the animal was actually 

 at work, in order to satisfy myself upon this point, 

 and have always perceived that the particles of soft- 

 ened rock fell from and on each side of the ligament 

 that binds the hinge, and extends to the- lowest 

 points of the valves.* Moreover, that this leathery 



* The reader must keep in mind, that since I was watching 

 the movements of my Pholas from beneath, my eye was as it 

 were at the base of the cavity for the hole was bored through, 

 and allowed the foot, and a portion of the shell of the animal, to 

 be distinctly seen. 



