PHOLAS STONE PIERCER. 201 



is, that the mollusks whose shells are per- 

 fectly smooth, are capable of producing the 

 same excavation as those which have a surface 

 as rough as a file. Many have supposed that 

 these animals possess some liquid which acts as 

 a solvent upon the substance they enter. This 

 appears the more probable, as they are known to 

 emit a phosphorescent light. 



The entrance is the smallest part of the dwell- 

 ing of the Pholades, and hence it is evident 

 that they must have penetrated the rock when 

 young and small, and enlarged their perforations 

 as they themselves increased in dimensions. The 

 position of the hole is always oblique to the 

 horizon : its form that of a truncated cone, 

 terminated by a rounded cavity. This cavity 

 receives the body, while the farthest end is 

 occupied by the proboscis, which is continually 

 protruded to the orifice to procure the sea water, 

 upon which it subsists. The proboscis is long, 

 pliable, and fleshy, terminated by a corneous 

 substance, which is dentated like a saw at its 

 extremity. There is an opening between the 

 valves, through which it is projected, and a case 

 into which it fits. At the approach of danger, 

 these mollusks, by means of this instrument 

 eject water to a considerable height, and its 

 dentated margin leads us to suppose, that they 

 also employ it in the work of perforation. 



