MARGARITACE.E ; PEARL-FISHERY. 403 



the shells, with the animals alive, to make perforations in them, 

 and then to commit them to their native element. The expense 

 of this proceeding, however, has been found to exceed the profit 

 obtained by it ; especially as the pearls thus produced are seldom 

 possessed of that regularity of form, which is an important 

 element in their value. The best pearls are generally produced 

 at the point, where the attachment of the adductor muscle causes 

 a roughness in the shell. The gradual change which takes place 

 in the position of this muscle, in accordance with the growth of 

 the animal, causes the detachment of the pearl ; and it is gene- 

 rally found imbedded in the substance of the muscle, by the 

 motion of whose fibres its regularly spherical form seems chiefly 

 occasioned. 



943. The formation of pearls is by no means confined to the 

 Amcula margaritifera. Any shell, univalve or bivalve, with a 

 nacreous interior, may produce them. They have been found in 

 Patellae (Limpets), Haliotides, and Pinnae ; and more especially 

 in the Unios, which are fresh water shells, abounding in most 

 rivers of the north.* It is the Pearl Oyster, or Mussel, as it 

 has been termed, which is most sought, as furnishing this com- 

 mercially-important article of luxury. The shell exists in con- 

 siderable banks in the Gulf of Manaar, on the shores of Ceylon, 

 the Persian Gulf, and other parts of the borders of the Indian 

 Ocean ; and also in the Gulf of Panama, and on the east shore 

 of California. It is attached by the byssus to submarine rocks, 

 usually at considerable depths. The most considerable bed is 

 said to occupy a space of twenty miles opposite Condatchy. To 

 prevent injurious destruction, the bank is divided as it were into 

 regular cuts ; one seventh part being worked every year, so as 

 not to exhaust the bed. The shells are brought up by divers, 

 who, by long practice, acquire the power of remaining under 

 water for four minutes, or even longer ; and in this time they 

 descend to the depth of from four to ten fathoms, pluck the shells 

 from their attachment, and accumulate about fifty in a net sus- 



* The River Tay in Scotland affords pearls which are held in tolerable estima- 

 tion ; although they are much inferior in clearness and lustre to the * orient 

 pearl.' 



