170 Economic Uses of Shells, and their Inhabitants. 



gently to jerk the line, when the cuttle-fish, attracted by the 

 appearance of the cowrie, darts out one of its arms, which it 

 winds around the shell, and fastens among the openings in. the 

 plates. The jerking being continued, the fish puts out 

 another and another arm, till it has quite fastened itself 

 to the shell-bait, when it is drawn up into the canoe and 

 secured. 



Pearl-producing shells. — The pearl-mussel, Unio margaritis 

 ferns, afforded the once famous British pearls. It is found in 

 the mountain streams of Britain, Lapland, and Canada, and is 

 used for bait in the Aberdeen cod-fishery. The Scotch pearl- 

 fishery continued till the end of the last century, especially in 

 the river Tay, where the mussels were collected by the 

 peasantry before harvest-time. The pearls were usually found 

 in old and deformed specimens. Round pearls, about the size 

 of a pea, perfect in every respect, were worth £3 or £4. An 

 account of the Irish pearl-fishery was given by Sir R. Redding 

 in the Philosophical Transactions, 1693. The mussels were 

 found set up in the sand of the river-bed, with their open side 

 turned from the torrent; about one in a hundred might 

 contain a pearl, and one pearl in a hundred might be tolerably 

 clear. 



Hyria is the shell which the Chinese employ to produce 

 artificial pearls, by the introduction of shot, etc., between the 

 mantle of the animal and its shell. A Hyria in the British 

 Museum has a number of little josses made of bell-metal, now 

 completely coated with pearl, in its interior. 



Pearls are produced by many bivalves, especially by the 

 oriental pearl-mussel (Avicula margaritifera). They are caused 

 by particles of sand, or other foreign substances, getting be- 

 tween the animal and its shell ; the irritation causes a deposit 

 of nacre, forming a projection on the interior, generally more 

 brilliant than the rest of the shell. Completely spherical 

 pearls can only be formed loose in the muscles, or other soft 

 parts of the animal. The Chinese obtain them artificially, by 

 introducing into the living mussel foreign substances, such as 

 pieces of mother-of-pearl, fixed to wires, which thus become 

 coated with a more brilliant material. Similar prominences 

 and concretions — pearls which are not pearly — are formed 

 inside porcellanous shells. These are as variable in colour as 

 the surfaces on which they are formed. They are pink in 

 Turbinella and Strombus ; white in Ostrea ; white or glossy, 

 purple or black, in MytiLm ; rose-coloured and translu- 

 cent in Pinna. (See specimens in Shell Gallery, British 

 Museum.) 



The pearl-fisheries of the Persian Gulf and Ceylon give 

 employment annually to several hundred boats and many 



