THE HARVEST OF THE TROPIC SEAS. 
the oyster shell itself. This is exported for manufacturing into knife 
handles, buttons, and articles of jewellery. So difficult is it to control 
the gathering of the pearls that they are regarded merely as an incident 
in the business, and are sometimes granted as a perquisite to the men. 
The shell, as soon as it is taken, is-opened on the deck with a knife, 
and any pearls that it may contain are scratched out with the fingers 
from the flesh in which they are embedded. 
Originally the shells were picked up from the surface of the coral 
reef by wading at low tide. When this situation was exhausted, natives 
were engaged to dive for the shell in shallow water. By degrees shell 
was followed down to water too deep for a swimmer to operate, and 
diving dresses were then introduced. The usual depth from which shell 
is procurable is 7 or 8 fathoms. Exceptional depths up to 20 fathoms 
may be reached, but work at such levels is difficult and dangerous. So 
heavy a mortality was caused by shelling in deep water that it was 
disallowed by regulation. 
Proposals were made to cultivate the pearl shell, but the experi- 
ments attempted have not yet been a commercial success. 
The head-quarters of the Queensland pearling fleet is Thursday 
Tsland, whence the vessels radiate to Torres Strait, New Guinea, and 
the Great Barrier Reef. The corresponding capital on the west coast 
is Broome. 
The Black-lip shell (Pinctada margaritifera) has a much wider 
range, both within and beyond Australia, than the previous species. But 
it is inferior both in size and in the quality of nacre and pearls. 
The Shark-Bay shell (Pinctada carcharina) is quite different in 
habits and appearance to either of the others. The shell, scarcely 3 
inches in diameter, is thin and poor, and can only be used for inferior 
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