PROCEEDINGS OF SECTION D. 547 
a few hours during the lowest ebb of the spring tides, proved to 
be admirably adapted for the purpose. At all other times a 
strong current, which is one of the most essential elements of 
their healthy growth, swept over them. Corals of the genus 
Madrepora, which will flourish in the purest and swiftly-circulating 
water only, were growing freely in these pools, and the conditions 
generally coincided closely with those under which the pearl-shell 
was in former times abundantly and may even yet be occasionally 
gathered in its adult state. For greater security, and in order 
that they might be more readily accessible for examination at all 
tides, the forty adult and about an equal number of young 
specimens that had been brought in by the A/Jatross were placed 
in wire netting-covered frames, closely resembling those that have 
for some years been successfully employed by me for the culture 
of ordinary oysters. In these frames the shells were raised 
slightly from the surface of the ground, and at the same time 
remained covered by a few inches of water at even the lowest ebb 
of the tide. Examined at short intervals during the remaining 
period of my stay at Thursday Island, about six weeks, all the 
specimens were found not only to be doing well, but to be growing 
rapidly. By the end of this relatively short period some of the 
examples had added as much as half an inch to the free border of 
their shells, and in almost all instances lappet-like prolongations 
of new shell were produced throughout this region. A corres- 
ponding rapidity of growth was also observed of the young shells 
having a diameter of two or three inches only, and including both 
those acquired in connection with the A/éatross expedition and 
the specimens previously obtained from the adjacent coral reef. 
Several examples from the stock ef pearl-shell accumulated 
were dissected for the purpose of preparing illustrations of the 
animal’s anatomy, and others were sacrificed with the object of 
ascertaining the capacity possessed by the living animals of 
repairing their shells, and the time occupied in such process. The 
results obtained in these several directions tended to show that 
the growth and maturation of the pearl-shell is effected within a 
much shorter interval than has been hitherto suspected. By 
many of those practically associated with the pearl-shell fisheries 
a period of from ten to fifteen years has been variously assigned 
to the mollusc as the time required for the growth of its shell to 
a marketable condition. Until the species has been under culti- 
vation or direct observation for a number of years, it will be 
impossible to accurately determine this important point. From 
the investigations recently conducted, and evidence otherwise 
collected, I am, however, inclined to anticipate that, under 
favourable conditions, a period not exceeding three years suflices 
for the shell to attain to the marketable size of eight or nine 
inches diameter, and that heavy shells of five or six pounds 
weight per pair may be the product of five years’ growth. In 
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