The consumption of oysters in London is enormous.  During the season of 1848-49, 130,000 bushels of oysters were sold in our metropolis.  A million and a half of these shell-fish are consumed during each season in Edinburgh, being at the rate of more than 7300 a day.  Fifty-two millions were taken from the French channel banks during the course of the year 1828; and now the number annually dredged is probably considerably greater, since the facilities of transport by rail greatly increase the inland consumption of these as of other marine luxuries.  French naturalists report, that before an oyster is qualified to appear in Paris, he must undergo a course of education in discretion; for the artificial oyster-beds on the French coast, where the animals are stored to be carried away as required, are constructed between tide-marks; and their denizens, accustomed to pass the greater part of the twenty-four hours beneath the water, open their valves and gape when so situated, but close them firmly when they are exposed by the recession of the tide.  Habituated to these alternations of immersion and exposure, the practice of opening and closing their valves at regular intervals becomes natural to them, and would be persisted in to their certain destruction, on their arrival in Paris, were they not ingeniously trained so as to avert the evil.  Each batch of oysters intended to make the journey to the capital, is subjected to a preliminary exercise in keeping the shell closed at other hours than when the tide is out; until at length the shell-fish have learned by experience that it is necessary to do so whenever they are uncovered by sea-water.  Thus they are enabled to enter the metropolis of France as polished oysters ought to do, not gaping like astounded rustics.  A London oyster-man can tell the ages of his flock to a nicety.  They are in perfection when from five to seven years old.  The age of an oyster is not to be found out by looking into its mouth; it bears its years upon its back.  Everybody who has handled an oyster-shell must have observed that it seemed as if composed of successive layers or plates overlapping each other.  These are technically termed ‘shoots,’ and each of them marks a year’s growth; so that, by counting them, we can determine at a glance the year when the creature came into the world.  Up to the epoch of its maturity, the shoots are regular and successive; but after that time they become irregular, and are piled one over the other, so that the shell becomes more and more thickened and bulky.  Judging from the great thickness to which some oyster-shells have attained, this mollusc is capable, if left to its natural changes and unmolested, of attaining a patriarchal longevity.  Among fossil oysters, specimens are found occasionally of enormous thickness; and the amount of time that has passed between the deposition of the bed of rock in which such an example occurs, and that which overlies it, might be calculated from careful observation of the shape