Page:The American Cyclopædia (1879) Volume XII.djvu/786

 772 fringes for more than a third of the length of the mantle. The adult oyster has no power of locomotion, and the only signs of vigorous movements are in the expulsion of the respira- tory currents, the excrements, and the sperm or ova by the sudden closing of the valves and OYSTER Oysters at different Stages of Growth. the contraction of the mantle ; but it is said they can turn themselves if placed upside down, and the sensibility of the fringes and labial pro- cesses is acute. The eggs are expelled in a white, greasy, viscid fluid, called " spats " by the fishermen, which adhere to submarine bodies, and to each other, by their develop- ment forming the immense banks found upon some coasts, the old ones being destroyed by the pressure of the new ; fecundation is effect- ed through the medium of the water, which conveys the sperm to the ova ; the eggs are to a certain extent developed within the cavity of the mantle about the gills ; to this cavity also the floating ova of some of the smaller Crustacea gain access, and here the little, soft, yellowish white crab (pinnotheres) is often de- veloped to a considerable size; this last is a parasitic inhabitant of the oyster shell, and is not a portion of its food, as the softness of the mouth of the latter does not admit of its at- tacking any resisting substance. Oysters are found in almost all seas, usually in from two to six fathoms of water, and never at a great distance from the shore; they are especially fond of tranquil waters or the gulfs formed by the mouths of great rivers ; they cannot live in fresh water, but some species remain dry during the greater part of every tide ; the tree oysters ( 0. parasitica and polymorpha), which attach themselves to mangrove and other bushes in the tropics, enclose within the shells a sufficient quantity of water to keep up the respiratory currents ; this faculty, possessed more or less by all the family, renders practi- cable their transportation to great distances. They have been highly esteemed as food from the times of the Greeks and Romans to the present day ; they are of easy digestion, but not very nutritious, and act rather as a provocative to appetite than as satisfying food ; they are eaten all the year round, except in the months of May, June, July, and August, which is the spawning season ; and they are good even then. The common oyster of Europe (0. edu- lis, Linn.), abundant on the coasts of Great Britain and France, occurs in large banks or beds, sometimes extending for miles, usually on rocky bottoms ; from about the middle of August to the middle of May they are dredged from the bottom by a kind of iron rake drawn by a boat under full sail, several hundreds being taken at a single haul ; these are trans- ferred to artificial beds or parks, where they are preserved for sale, continually growing in size and improving in flavor. The growth of the oyster is slow, it being only as large as a half dollar at the end of four to six months, and twice that size at the end of a year ; in artificial beds the growth is usually slower, the full size not being attained till the fifth to the seventh year. The west coast of Scotland and the Hebrides have the best oysters of the British coasts, and here in sheltered bays they acquire the green color so esteemed by the epicure, and supposed to be due to confervas and similar colored growths in the breeding places ; other English beds extend from Graves- end on the Thames along the Kent coast, and in the estuaries of the Colne and other rivers along the Essex coast. The British beds are kept up by careful culture and by the introduc- tion of broods from all quarters; since 1872 several varieties of American oysters have been introduced, but the planting is still an experi- ment, and it is said that the change of sea de- teriorates their quality. Not many years ago the beds of France were nearly exhausted ; in 1858 M. Coste recommended plans for their restoration, and since then the parks in the bays of St. Brieuc and Arcachon, and the isle of Re, restocked by broods from Cancale and other sources, have become enormous; and the successful culture is yearly extending along the entire Atlantic and Mediterranean coasts of France. The Danish coast is Avell supplied with beds. The Neapolitan lake Fusaro is the great oyster park of Italy. The species most esteemed in America are the Virginian oyster ( 0. Virginiana, Lister) and the northern oyster (0. lorealis, Lam.). In the 0. Virginiana the shell is elongated and narrow, and the beaks