1922] MADRAS PEARL FISHERIES 149 



the animals which lodge the adult stage, we cannot formulate any 

 plan for furthering the increase in numbers of those of the larval 

 stage, whose presence in the pearl oyster controls the production of 

 valuable pearls. 



The ratio of infection — and of consequent pearl production — ■ 

 varies greatly as is to be expected consequent upon the local 

 abundance or otherwise of the host of the adult parasite whatever 

 it may be, and also upon the relative profusion or scarcity of the 

 oysters themselves. 



Time after time I have proved by the dissection of large 

 numbers of oysters of the same age from different beds that the 

 cestode infection may vary within considerable limits and as a 

 consequence the pearl yield is proportionately variable. For 

 example in November IQ02 samples of the same generation of 3/4 

 to 3^2 years old oysters were obtained from four different beds, 

 with valuation results as follows : — ■ 



RS. 



Periya Par Karai ... ... ... 13 



South-east Cheval ... ... ... 10 



Mid-east Cheval ... ... ... 18 



North-east Cheval ... .. ... 23 



In March 1887, oysters of a similar age from the Moderagam 

 Par gave a pearl valuation yield of but Rs. 9-14-3 per 1,000, while 

 other individuals of identical age from the North-west Cheval in 

 the same year were valued as low as Rs. 6-15-O per 1,000. 



Another instance of wide variation in pearl yield occurred in 

 the valuation of the 4% to 4 3 A years old oysters fished this year 

 (1904) from the Western Cheval. Three lots varied as follows : — • 



rs. a. p. 

 South-west Cheval ... ... ... 36 o o per 1,000 



North-west Cheval ... ... ... 33 12 o ,, 



Mid-west Cheval ... ... ... 20 4 o , 



With such wide divergence in oyster value from closely adjoin- 

 ing areas we can never be sure of the pearl yield from a particular 

 bank till we solve the riddle of the pearl cestode's life-history and 

 are enabled to increase artificially the proportion of infected 

 oysters — a matter for marine biological investigation. 



Meanwhile it is satisfactory to know that the oysters which the 

 Tolayiram Par rears are of fair quality and capable of giving a 

 high pearl yield. 



