THE OYSTER AND ITS MODE OF LIFE 9 



Lister) on the Atlantic coast of Canada and the United States. A small 

 distinct species (0. lurida, Carpenter) occurs on the Pacific coast of Canada, 

 extending southwards to California. 



Distribution. — In geological distribution the genus Ostrea dates from 

 the Carboniferous era, and reached its culmination in the Cretaceous, 

 when tv.^o other genera (Exogyra and Gryphsea) became extinct. Geo- 

 graphically, it is to be found in waters adjacent to every continent, but 

 especially to the south and west of Europe, on both sides of America, the 

 east and south of Asia, and south of Australia. The North Atlantic with 

 its extensions into America (gulf of St. Lawrence and gulf of Mexico) and 

 into Europe (Mediterranean, Adriatic and Black seas, bay of Biscay, 

 English channel and North sea) is the great oyster-producing ocean of the 

 world. Japan, China, India, Java, Australia, Tasmania, New Zealand, 

 Brazil, California, British Columbia, and some other countries not within 

 its bounds, have a relatively small production. Nowhere do oysters 

 occupy such extensive, continuous areas as on the eastern coast of the 

 United States, the greatest oyster-producing as well as the most lavish 

 oyster-consuming country in the world. From cape Cod to the gulf of 

 Mexico is one vast, almost uninterrupted area, with Chesapeake and 

 Delaware bays as the centre of most profuse production, and Baltimore 

 as the greatest oyster market in the world. 



On the Atlantic coast of Canada oysters occur at many places, from 

 Chaleur bay along the coast of New Brunswick and of Nova Scotia to near 

 the strait of Canso, on both sides of Prince Edward Island, in the Bras 

 d'Or lakes of Cape Breton, and very sparingly at a few places on the south 

 shore of Nova Scotia to the east of Halifax. The centres of greatest pro- 

 duction are Miramichi bay, N.B., and Richmond bay, P.E.L 



Habitat. — Oysters occur in shallow bays and estuaries of rivers, 

 where the water is warmer and less saline than that of the sea, and where 

 there is also a greater abundance of suitable food. Adult oysters cannot 

 swim, creep or burrow, but are normally fastened upon the left side to a 

 rock, shell, or other submerged object. As the older oysters die off young 

 ones build upon their shells, until the mass broadens and thickens into a 

 more or less extensive bed. Small, isolated clumps of oysters also occur, 

 and many individuals become broken loose and rolled about by 

 disturbances in the water. 



Food. — As the oyster cannot go in search of food, it has to depend 

 upon that which is produced by the water of its immediate vicinity, or 

 brought to it by currents. As it has neither jaws nor teeth, it cannot make 

 use of anything except the smallest particles of food-material. Both of 

 these conditions are met by the vast numbers of minute plants and animals, 

 — particularly the group of the former called diatoms — that swarm in the 

 water and constitute a great part of what is known as " plankton ". These 



