Page:Natural History, Mollusca.djvu/248

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ciently abundant to pay for dredging. The sea-oyster is often, before being brought to market, kept for a time in artificial beds, in order to improve its flavour.

"The most esteemed oysters are those of the small ovate, but deep-shelled variety, called Natives, among which, those of the river Crouch, or Burnham Oysters, are pre-eminent for the marine flavour; probably on account of the facilities for rapid importation of them in fine condition. Much of the quality depends on the ground and condition of the beds: the oysters of different years from the same place often vary materially in this respect. They are considered full-grown for the market when from five to seven years old; sea-oysters at four years. The age is shown by the annual layers of growth, or 'shoots,' on the convex valve. Up to three or four years, each annual growth is easily observed, but after their maturity it is not so easy to count the layers. Aged oysters become very thick in the shell. In the neighbourhood of fresh water the oyster grows fast, and improves in body and flavour. The flavour is said by some to improve by shifting the oysters as they approach their full growth. Frost kills numbers, and when they are left dry at low ebbs, the run of fresh water from the land turns them, what is called, 'foxy,' of a brownish red colour. They are sometimes seized with sickness during the spawning season, and considerable numbers may die. Much labour is required to keep the beds in good order, cleansed from shells and rubbish, star-fishes, barnacles, corallines, and sea-weed, which grow freely in the spring of the year. On the cleanliness of the ground the prolific character of the bed, if the