Royal Physical Society. 401 



rich In its natural supplies ; that it will move from its 

 original situation if the water becomes impure, either from 

 the decomposition of vegetable or animal matter, or muddy, 

 and probably too, if there is a large influx of fresh water ; 

 that if the water is agitated to an inordinate degree, the 

 oyster will leave its old mooring-place and seek another ; 

 that a thunder-storm will kill some in an aquarium (query, 

 if thunder storms have similar fatal effects on oysters lying 

 deep in the sea ?) ; that the animal can unfix itself from its 

 byssus, and that crabs, shrimps, and other creatures, force 

 them to form a new byssus, by nibbling through the old one ; 

 that it can re-form its byssus at pleasure, if in good health 

 and condition ; that it can live for a long time without form- 

 ing a byssus, and that it will re-form a byssus when it has 

 recovered strength ; that the power of re-forming its byssus 

 is not confined to the young animal, but that the largest 

 living oyster I have seen can re-form it in an aquarium-, as well 

 as in the depth of the sea, but not so actively as the young 

 and middle-aged. Pearl oysters are gregarious in their habits. 

 In placing several young oysters in different parts of an aqua- 

 rium, they will sooner or later be found attached to each other. 

 The older ones have also this desire ; but their heavy shells iru- 

 .pede their motion, and they are contented to remain apart from 

 their fellows. That, taking the foregoing facts into account, 

 there appears to be no reason why pearl oysters should not be 

 translated from their native beds, and made to colonize other 

 parts of the sea. That the young, as well as the old, are in 

 spawn from March to September, and that probably there is 

 no stated period for spawning. The whole occupation of the 

 oyster, when fixed to a spot, appears to be, keeping its valves 

 open, and admitting food to its mouth. For several hours the 

 valves remain open ; they then close for a few minutes, or 

 for an hour or two, then open again. At night the valves 

 remain generally open till towards daylight, when they close, 

 and remain so till the sun shines brightly over the horizon. 

 It is during the early part of the night, or soon after sunset, 

 that they exercise, tuJien required, their locomotive powers. 

 I have watched the oysters in aquaria for nearly a whole night, 

 and they appear to be then active in moving and attaching 



