196 MULTIVALVES. 



as a file. Many have supposed that the animal 

 must possess some liquid which acts as a solvent 

 upon the substance it enters. This appears the 

 more probable, as it is known to emit a phos- 

 phorescent light ; but as the Pholades pierce 

 substances of so very different natures, it appears 

 that the same substance could not act as a sol- 

 vent to them all. 



The difficulty in accounting for the manner in 

 which this little animal forms its retreat, should 

 teach us how easily human reason is baffled, and 

 lead us to reflect upon the condescending wisdom 

 displayed for the accommodation of a slug. The 

 entrance is the smallest part of the dwelling 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 posi- 

 tion 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 probos- 

 cis, which is continually protruded to the orifice 

 to procure the sea water, upon which it subsists. 

 The proboscis is long, pliable, and fleshy, termi- 

 nated by a corneous substance, which is den- 

 tated 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, the mollusca, by means of 

 this instrument, eject water to a considerable 

 height, and its dentated margin leads us to sup- 

 pose, that they employ it in the work of perforation. 



