46 P H O L A S. 



May not tills process be forwarded by chemical as 

 well as mechanic means ? May not the peculiar 

 secretion, which, both in the body of the animal, 

 and when separated from it, emits a phosphores- 

 cent light, act in some degree as a menstruum on 

 calcareous matter, and woody fibre ? If so, the 

 difficulty of procuring an entrance, and of enlarging 

 the internal chamber, would be much diminished. 

 It appears, indeed, scarcely possible that these 

 Mollusca should be able to obey the instinct of 

 their nature without some aid from a softening or 

 dissolving fluid. They are doubtless deposited, as 

 soon as formed, in the superficial cavities of the 

 rock or wood ; for they are usually discovered iu 

 great numbers about the same place, as if from the 

 ovary of a common parent. 



The accessory valves are affixed to the hinge and 

 upper margin by a gelatinous substance, which is 

 liable to decay after the death of the inhabitant : 

 hence arises the circumstance of their being found 

 very frequently defective. 



