THE LIFE-HISTORY AND HABITS OF THE PEARL OYSTER. 137 



estimate in March, L900. In his report on the inspection of that date he announced 

 the discovery of two wide-spread falls of spat over the Cheval and Muttuvaratu paars, 

 which must have taken place about June and December, 1899, respectively, as he 

 gave the ages, when found in March, 1900, as from 3 to 9 mouths. Consequently 

 the oysters fished from the East Cheval Paar in the spring of 1903 cannot have been 

 older than 3 to 3f years, a conclusion Avhich makes the yield of pearls in this last 

 fishery an eminently satisfactory one considering the comparative immaturity of the 

 oysters. We must also conclude that, notwithstanding differences in size and 

 appearance, the oldest oysters on the Muttuvaratu Paar and on the Cheval Paar are 

 of the same age, as they are grown from the spat which Donnan found in March, 

 1 900. 



A sample of 50 adult oysters from the Muttuvaratu Paar, measured in April, 1902, 

 gave as the average 2^- X 2^j inches, or 55 - 50 X 511) millims.* A sample of 

 38 oysters from the same bank, measured in November, 1902, gave an average of 

 58"84 X 54 - 32 millims., by 22 - 07 millims. in thickness. Twelve oysters from the same 

 locality, measured in March, 1903, gave an average of 57 "54 X 54'0 millims., by 

 24"42 millims. in thickness. 



These, figures show an increase during 7 months (April to November, 1902) ot 

 3"34 millims. X 3"32 millims., with a slight decrease during the ensuing 4 months. The 

 very slight increase during the former period, and the arrest of growth after that, agrees 

 well with the impression we formed as to this bank from the oysters we have seen. 

 Coral growths are very rich on the valves along with other incrusting organisms 

 Polyzoa, Sponges, Tunicates, and Algse chiefly. The oysters are small but thick, 

 with no marginal processes or " fingers." If they have ceased to grow superficially, 

 they are adding to the thickness of the shell. Our field notes say (November, 1902) : 

 " The pearl oysters on this bank are more thickly crowded than on any other ; their 

 size is the most stunted of any yet seen, and they are thin and miserable within, 

 with little food in the alimentary canal in most cases." In March, 1903, when 

 Mr. Hornell inspected the bank with the diving apparatus, he found that the 

 oysters were densely crowded together, approximately 125 to the square yard, along 

 with various other animals, chiefly corals, which were both on and around the oysters. 

 He noted " The oysters were all small and stunted and unhealthy looking, showing 

 no vigorous shell growth and no marginal processes. On dissection, it was found that 

 all those collected had internally the same stunted appearance. The bodies of all were 

 equally shrunken and thin, the gonads spent or not seasonably developed, and at the 

 best, extremely small ; indeed all tissues were equally meagre, even the byssus weak 

 and of few strands." We have other observations, and extracts might be multiplied, 

 all tending to show that the poorly nourished and diseased condition of the oysters on 

 the Muttuvaratu Paar is due to overcrowding. 



* The first measurement given is always the depth (dorso-ventrally. at right angles to the hinge), and 

 the second the length (antero-posteriorly). 



T 



