OF THE GULF OF MANAAR. 
103 
adapted for giving holding ground to facilitate the growth 
of minute algte, while the fine interstices between the closely 
overlapping spines and the continuous crevice under every 
flange afforded with the algfe, the most beautiful shelter for 
infusoria. Seeing then that the young oyster is in every 
individual studiously provided with a shell specially con- 
structed both for sheltering the food of the young oyster 
and for rearing the food of that food, it seems to follow that 
it is a great and primary necessity to every young pearl 
oyster to be thus independently supplied with a moveable 
commissariat, and it indicates that to have such a necessity 
a migratory habit must be one of the laws of its existence. 
In brief the testaceous covering indicates the habit of the 
tenant. 
It may serve to give us a clue in a further direction also. 
The spines present on the shell of the young pearl oyster 
are locally said to be absent from the older oyster. On 
this point I have had no opportunity of making personal 
observations, for as I have said we came on no mature live 
oysters, and no reKance could be placed on dead shells that 
might have been subjected to abrasion -. and the shells kindly 
shown me in Ceylon had all been rubbed smooth by way of 
cleaning. I note here that Reeve's Conchologia Iconica has 
the remark : "as the shell advances in age and the valves 
thicken the sculpture becomes obsolete." This remark is 
made of the giant pearl bearer Avicula {meleagrina) mar- 
garitifera, the shell of which is 7 inches across from hinge 
to contour, and can only be taken quantum valeat as confir- 
matory of the local opinion of our Avicula {meleagrina) fucata, 
which is only 3| inches across at maturity. Presuming 
that the local information is accurate on this point, and as 
opportunity occurs of examining mature oysters, it is to be 
hoped that it will be tested, it seems to indicate the con- 
elusion that there comes an age when, from the increased 
thickness and weight of their shells, pearl oysters cease to be 
