PEARL AND PEARL-SHELL FISHERIES. 219 



to be admirably adapted for the purpose. At all other times a strong current, which is one of the 

 most essential desiderata for healthy growth of the animals, swept over them. Corals of the 

 genus Madrepora, which will flourish in the purest and swiftest 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 equally numerous young oysters that had 

 been brought in by the Albatross were placed in wire-netting-covered wooden frames, closely re- 

 sembling those which had for some years previously been successfully employed by the author for 

 the culture of ordinary oysters. In these frames the shells were raised slightly from the surface 

 of the ground, and they at the same time remained covered by a few inches of water, at even the 

 lowest ebb of the tide. Examined at short intervals throughout the remaining period of the 

 author's 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 short period, some of the examples 

 had added as much as half-an-inch to the free borders of their shells, and in almost all instances 

 lappet-like prolongations of new shell were produced at this growing region. A correspond- 

 ing rapidity of growth was observed for the young shells having a diameter of two or three 

 inches only, including both those acquired in connection with the Albatross expedition and the 

 specimens previously obtained from the adjacent coral-reef. 



Several examples from the stock of pearl-shell accumulated, were dissected, for the purpose 

 of preparing a diagram 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 when mutilated, 

 and the time occupied in that process. The results tended to show that the growth and maturation 

 of the pearl-shell is effected within a much shorter period than has been suspected. By many of 

 those practically concerned in the pearl-shell fishery, a period of from ten to fifteen years has been 

 variously assigned to the mollusc, as the time required for the growth of its shells to a marketable 

 condition. Until the species has been under cultivation or continuous observation for years, it will 

 be impossible to determine this important point. From the investigations then and subsequently 

 conducted, and from data otherwise collected, the author is inclined to think that under favourable 

 conditions a period not exceeding three years suffices for the shell to attain to the marketable size 

 of eight or nine inches diameter, and that heavy shells of 5 lb. or 6 lb. weight per pair may be 

 the product of five years' growth. In connection with the experiments concerning the artificial 

 cultivation of the pearl-shell, it was the author's desire to make himself acquainted with the 

 reproductive phenomena of the species, of which up to that time no accurate information was 

 available. In none of the specimens dissected, nor in the more numerous examples opened on the 

 shelling grounds, however, were the reproductive organs mature. From this it is thought that 

 the principal spawning season of this mollusc occurs during the calmer and hotter period of the 



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