THE LIFE-HISTORY AND HABITS OF THE PEARL OYSTER. 



141 



This gives an increase of only 0'8S X 0"65 millim. for the 4 months ending March, 

 1903, which bears out the statement made above that growth after the third year is 

 very slow. Comparison with the growth of the much younger (second year) 

 oysters on the South-west Cheval, from 50'57 X 47 '52 millinis. in November, 1902, 

 to 54 - 41 X 4975 millims. in March, 1903, shows how very rapid the increase is at 

 this age, 3"84 X 2 - 23 nhllims. in 4 months. 



As, however, the shell can grow in thickness of valve as well as in superficial 

 extent, it is of some importance to consider the weight in relation to age. We are 

 able to give a table of the weights of shells of one generation of pearl oysters as 

 determined by Captain Donnan annually from the first year to the time when fished 

 at 4 and 5 years of age. As after the third year there is but little increase in size, 

 the figures for the later years may be taken as indicating the additions to the 

 thickness of the shell. 



Weight of Cleaned Pearl-oyster Shells. 



The stunted condition of the oysters on the Western Cheval which we saw on the 

 ground, and have noted elsewhere in this report, is shown by these figures to have 

 been as marked a quarter of a century ago. While the South-east Cheval produced 

 shells which at 3 years of age weighed 21 J drams each and at 4 years 30 drams, 

 those of the same ages from the North-west Cheval weighed only 19 drams and 24|- 

 drams respectively. 



All the above figures, as well as the non-numerical observations which we made 

 upon the banks during two inspections and a fishery, tend to show that, of the 

 reliable paars, the Southern and Eastern parts of the Cheval, the Periya Paar Kerrai 

 and the North Modragam are, at present, those that produce the most rapid growth 

 and healthy development of the pearl oysters. The conditions at these paars which 

 seem to determine the good results are : 



