INTRODUCTION 7 



There is much that we agree with in all of these previous reports. There are some 

 points in each on which we differ from the author. We account for the occurrence in 

 another way, or draw a different conclusion from the observed facts. Several of these 

 writers, although not strictly speaking scientific men, were accurate observers and 

 acute investigators who have left valuable records. Others better equipped in 

 scientific training have been prevented from doing more by unfavourable circumstances. 

 Dr. Kelaart's short reports show that he was tackling the problems in a scientific 

 manner, and his researches were incomplete at the time of his sudden death.* 

 Mr. Holdsworth's visit to Ceylon (18G5-69) was apparently made at an unfortunate 

 time. Mr. Oliver Collett states (' Journ. II. Asiat. Soc.,' Ceylon, Br., 1900) that 

 Mr. Holdsworth never had an opportunity of seeing a fishery, and according to 

 Sir W. Twyxam, he " did not witness an inspection of a bank with a bed of oysters 

 on it, young or old." Mr. Hornell and I were more fortunate, as during our cruises 

 in the Gulf of Manaar we found pearl oysters in all stages of growth, from the 

 microscopic free-swimming larvae and newly-deposited "spat" to the pearl-bearing 

 adults, and we have also two consecutive inspections of banks well covered with 

 oysters, and the successful fishery of 1903, from which to draw conclusions. 

 Mr. Thurston, of Madras, has also had experience of fisheries and inspections with 

 Captain Donnan, and has written a most interesting and valuable record containing 

 a great deal of incidental information as to the fauna of the Gulf of Manaar, but had 

 apparently not the opportunity and the implements for a more detailed survey, nor 

 the time for a more thorough investigation of the ovster problems. 



To all our predecessors, however, we are indebted for information and for sugges- 

 tions which have been of value to us in our work. That work has led us into various 

 different lines of inquiry. Outside the larger influences, cosmic in origin, uncontrol- 

 lable, and wide-spread in effect, such as oceanic currents, monsoon storms, depth of 

 water, configuration of bottom, and shifting sands which may devastate a bank and 

 cause the sudden disappearance of many millions of oysters, there are, in addition, 

 various minor causes of failure of the fisheries, some of which we were able to 

 investigate. The pearl oyster has many enemies, such as Star-fishes, boring Sponges 

 which destroy the shell, boring Molluscs which suck out the animal, internal Proto- 

 zoan and Vermean parasites, and carnivorous Fishes, all of which cause some destruc- 

 tion, and may on occasions conspire to ruin a bed and change the prospects of 

 a fishery. But, in connection with such animate foes, it is necessary to bear in 

 mind that, from the fisheries' point of view, their influence is not wholly evil, as some 

 of them are closely associated with pearl production in the oyster. One enemy (a 

 Plectognathid fish), which doubtless devours many of the oysters, at the same time 



* Soon after the fishery of 1859, during which Dr. Kelaart worked with the Swiss Naturalist, 

 Humbert, at Chilavaturai, he was sent to England in medical charge of General Lockyer, who was very 

 ill and died in the Red Sea. Dr. KELAART, who was in constant attendance on the General, died suddenly 

 a day or two later. 



