OF THE GULF OF MANAAR. 
109 
growth very great ; but when the circumstances are alto- 
gether different as in the case of an oyster attached to a 
buoy, one naturally expects to find a very marked difference 
in the health and growth of the animal. But when the 
differences in the surroundings are less marked, we expect 
to find the effect on the growth correspondingly less marked 
also. Thus in a bank of oysters we find that those which 
have contrived to get by themselves are larger than those 
that are thickly clustered, and in such cases the variations in 
growth are naturally variations of degree, such as might 
easily account for the difficulty the divers experienced in 
ageing all individuals. It is interesting also to observe that 
any individual oyster that is growing more rapidly than its 
fellows has the soft edge, which is the growing edge, longer 
in comparison than the soft edge of a slower growing 
neighbour, the shells of some of the most backward of which 
are stunted. It is a very natural indication of varying 
rapidity of growth, which I also have observed in a less degree 
in the horn of the antelope, though there the case is more 
complicated than in the oyster. Again, we find that the 
system of ageing pursued on the two sides — the Ceylon and 
the Madras sides — of the Grulf of Manaar differ, and we are 
hardly justified in jumping therefrom to the conclusion that 
the whole set of divers and the experienced Superintendent 
on either side is in error. Once more we find that the same 
oyster on the Ceylon side grows at maturity to a decidedly 
larger size than any to be found on the Madras side, which 
is an indication that the conditions of Kfe are more favor- 
able to the oyster on the Ceylon side than they are on the 
Madras side, and, taken in connection with the different 
rate of ageing on the two coasts, another indication to 
be added to the several instanced above that the rate of 
growth of the pearl oyster varies with its surroundings. 
Indeed it would be strange if such a widespread rule did not 
obtain in a greater or less degree. Allowing then for ita 
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