164 MADRAS FISHERIES BULLETIN VOL. XIV, 



bottom, rocks, stones and shells, in depths from 5 to II fathoms. 

 In Palk Bay they occur on muddy bottom or rather just where the 

 purely muddy bottom merges into muddy sand at a very uniform 

 depth of 5^2 fathoms. On this bottom there are no stones, only 

 occasional dead shells, the valves of Arcti, Modioli and Placiiiia 

 chiefly. To this precarious foothold the pearl-oysters attach. In 

 1914 they were found in sufficient numbers to justify an experi- 

 mental fishery. Though the result showed only a small profit, the 

 fishery was of great benefit to the villages in the neighbourhood, 

 bringing a considerable amount of money into circulation. 



It is probable that the permanent habitat of the pearl-oyster in 

 South Indian waters is in Palk Bay and that the beds which were 

 recently discovered there give rise to the spat that repopulate from 

 time to time the banks in the Gulf of Mannar.'" 



In the Gulf of Kutch a pearl-fishery is carried on by His High- 

 ness the Maharaja of Nawanagar. The oysters there do not form 

 banks; they occur scattered along the low-water edges of the 

 rocky reefs that abound on the Nawanagar coast. They are 

 collected l:)y men wading in the shallows at low water of spring 

 tides. 



The shell of the common Indian pearl-oyster is too thin for 

 manufacture into any but the most inferior quality of small pearl 

 buttons. Pearls are the sole object of the fishery ; the shells are 

 of such little value that they have usually been left derelict by 

 their owners at the end of a fishery. 



The origin of pearls has long been the subject of speculation, 

 but it was not till 1912 that the subject as concerning the Ceylon 

 and Indian pearl-oyster was systematically investigated. In that 

 year Professor Herdman and the writer went to Ceylon by request 

 of the Government to investigate this and related questions. The 

 result was to show that pearls belong to two main classes, orient 

 and muscle pearls. The best of the former usually owe their 

 origin to the irritation set up by the presence of a parasitic worm 

 larva in the mantle. To get rid of the trouble the oyster covers 

 the intrusive body with layer after layer of nacre, thus forming a 



* The anatomy of the Pearl-oyster is described by Herdman and Hornell in Volume 11 

 of the Ceylon Pearl Fisheries Reports, Royal Society, London, 1904, while the Madras 

 Fisheries Bulletin, Reports IV and II of \'ol. \'11I, should be consulted respectively 

 for information regarding the pearl beds in Palk Ba}' and the factors governing the 

 irregularly cyclic occurrence of Indian pearl fisheries. 



