not be done simply by the weight of the lid, as before. Now, if we unlock the desk, up springs the lid, raised by the expansive force of the rubber at the hinges. This is precisely one of the functions of the hinge-ligament of the oyster. When the animal desires to shut up the valves, it contracts the great adductor muscle. When it needs to open them, it relaxes that muscle, and the valves open of themselves. Patrick's mishap was not merely amusing, regarded as a blunder, but even more so when viewed in this physiological light. He was told to go into the cellar and bring up some oysters in the shell; and his mistress gave him a strict charge not to bring any that were dead.
Fig. 7.—Organism of an Oyster
Patrick brought up a tray full, and every bivalve upon it was gaping wide! In reply to the astonished look of his mistress he said: "Sure, mam, they must be alive, or how could they keep their mouths open?" "But, Patrick," urged the lady, "could you not tell the difference by the smell?" "And sure, mam, I was remarking that same to meself. But mightn't the others have bad breaths too, if they'd only open their mouths a bit?" Had the matter been pressed to an explanation, perhaps the mistress would have been as severely taxed as the servant to render a reason.
The growth of an oyster-shell is always at the edge. It is effected by the rim of the mantle, as a series of delicate tips assorting the lime which is held in solution in the sea-water, and most daintily laying in
