236 Conchology. 



too fatally known. These concretions, no doubt, owe their ori- 

 gin to the diseased or unhealthy action of the vessels secreting the 

 fluids in which they are formed. By this diseased action produc- 

 ing a super abundance of the matter, which enters into the com- 

 position of the concretion; or this matter in the fluid state, meeting 

 with some solid body, which becomes a nucleus, is attracted by 

 it, and deposited in concentrib layers, till the concretion acquires 

 a larger or smaller size, according to the duration and quantity of 

 the secretion and deposition. In the same way, it seems extremely 

 probable the pearl may be frequently formed; the matter of which 

 it is composed, being constantly secreted by the animal for the 

 production of the new part of the shell. If then, this matter 

 should at any time be produced in greater quantity than what is 

 necessary to form the inner layers of the shell, and particularly if 

 it should meet with a solid particle of any body, it will be attract- 

 ed by it, and thus constituLe the rudiments of a pearl, which will 

 receiv'e constant additions of concentric layers, and increase in 

 size, in proportion to the age of the animal, and the quantity of 

 matter deposited. Pearls, it is said, have been found within the 

 body of the animal. If this be true, the pearly matter, in its pas- 

 sage through the vessels of the body, must have met with some 

 •nucleus, around which the concentric layers have been founded. 

 In most cases, however, the pearl is found loose in the shell, en- 

 tirely detached from the animal. It must then have been formed 

 of the matter, which was thrown out of the body, but it is not 

 unlikely that pearls are found both ways, or that the same pearl 

 may be partly formed within the body of the animal, and be after- 

 wards excluded, and arrive at its utmost size, while it remains 

 loose in the shell. 



But according to others, the pearl owes its formation to some 

 external injury. The following seems lo be a pretty distinct view 

 of this opinion. When Taujas de St. Fond visited Loch Tay, he 

 was led to make some inquiries concerning the pearl fishery, which 

 had been carried on in several parts of the river Tay for some 

 years. Shells were brought to him, and in these shells the fisher- 

 men pretended to find pearls, which they expected to sell at a 

 higher rate, as they were found in the presence of the traveller. 

 But he informs us, that they attempted to impose on him, by in- 

 troducing a pearl secretly into the shells as they opened them. 

 Observing this circumstance, he told them that he could know at 

 once, by examining the outside of the shell, before opening it, 

 whether it contained any pearl. He mentions this to introduce 

 some speculations concerning its formation. When no perforation 

 or callosity appeared on the outside, he concluded that there was 



