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MOLLUSCA.

removal necessary, as has repeatedly happened in the dockyard of Plymouth. To preserve the timbers used there, and exposed to them, the plan now adopted is to cover the parts under water with short broad-headed nails, which, in salt water, soon invests the whole with a strong coating of rust impenetrable by their augers. The plan appears to have proved effectual, for, in the harbours of Plymouth and Falmouth, where the Teredo was once abundant, it is now rare or not to be found; but in other parts it has still a residence, and within these few years it has materially injured or destroyed many of the piles used in the construction of the pier at Port Patrick, on the coast of Ayrshire; and the Limnoria terebrans, a crustaceous insect, co-operating with it, the result of their united efforts can hardly fail to be the utter and speedy destruction of all the timber in the pier."

Another kind of injury is dependent on the fact that certain species, which are generally eatable and even wholesome, become at certain times highly poisonous. Some foreign species are liable to this fatality, particularly oysters, both in the East and West Indies. But we need not go to distant countries for cases in point. The Mussels of our own rocks, though generally sold and eaten by many persons without fear, are well known to be fickle in their qualities, and many cases are on record in which their use has proved fatal. One of these, well authenticated, and investigated by scientific medical men, occurred at Leith in June 1827. Many of the poor of this town were poisoned by eating mussels which had been collected in the docks.