386 SUPPLEMENT 
artificial means. Linneus has effected this in the shells of 
the genus Unio, in the rivers of Sweden. By piercing the 
shell while the animal is living, the formation is induced, at 
the corresponding part of the interior, of a pearly mass, which 
will present the desired size and form. 'The Swedish govern- 
ment at first made a secret of this invention, and established 
artificial pearleries; but at the end of a few years it was 
obliged to abandon them, the advantages of the undertaking 
being very far from counterpoising the expence ; because, in 
the number of pearls which were formed, it was very rare to 
find any of the slightest value.” 
The inhabitants of India appear to pursue a system pretty 
nearly analogous to this. We find sometimes in collections, 
though not often, the large shell which produces the most 
numerous and the finest pearls, crossed by a thread of brass- 
wire, in a part of its length, and we see in the interior, 
some crumplings, or blisters of the nacre, which indicate 
that pearls might be found there. A fluviatile shell, from 
China, has been seen penetrated by a brass-wire, rivetted 
externally like a nail-head, while the part which penetrated 
inside had a very well formed pearl, soldered, as it were, to 
its extremity. 
Pearls are also said to be obtained by depositing in a living 
shell, a very small piece of spherical nacre, in a place where 
the mantle is raised up, and the nacreous paries scratched. 
This mode is reported to have been tried with success in 
Finland. It has been even said, that certain Asiatics intro- 
duced into shells little works of handicraft, which, in the 
course of time, are invested with the substance which forms 
the pearls. 
We have already observed, that it is easy to imagine that 
all the nacreous shells may produce pearls. Thus we find 
them sometimes in the patelle, the haliotides, and the pinne ; 
but in general, they are more especially produced by the 
“oe 
