46 
PHOLAS. 
May not this 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 in 
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. 
