1.The oyster is called a shell-fish；but it is not a real fish，like the sole or the herring.All true fishes have a backbone，and they swim about in the sea by the help of their tail and their fins.
DREDGING FOR OYSTERS（用捞网捉牡蛎）
2.But the oyster has no backbone；indeed it has no bones at all.Its soft body is protected by two hard shells，between which it lies.
3.One of these shells is larger than the other；and it is by the larger one that the oyster fastens itself to the rocks or to the muddy sea-bottom where it lives.
4..T h e t w o s h e l l s a r e joined together by a hinge①；and the oyster has a strongpiece of flesh，or a muscle，by which it can keep them shut.If you take an oyster out of the water，you will find that it holds its two shells so tightly together that you cannot pull them apart.
5.Oysters are usually opened with a knife；but by being put into boiling water they can be killed in a moment，and the shells then open easily.Look inside an empty oyster-shell，and you will see a little hollow where the muscle was fixed to the shell.
6.The inside of the shell shines like pearl；indeed，it is from a kind of oyster that pearls②are got.The oyster makes both the shell and the pearls out of matter whichit finds dissolved in the sea-water.
7.The oyster has a little mouth，a stomach，and other organs③.It breathes like a fish by sucking air out of the sea-water with its gills；and it also gets its food out of the sea-water.
①Hinge，the joint on which anything hangs and turns.
②Pearls，small，white，and shining gems found in some shellfish.
③Organs，members of the body.
8.It takes the sea-water into its mouth，and lets it run out through its gills.But any tiny living things which may be in this sea-water are caught and swallowed，and go into its stomach.
9.The best oysters are found round the mouth of the river Thames①，in the English Channel，and on the coasts of France.
10.In the summer months the oyster lays its eggs，and millions of young ones are born.They are no bigger than pin-points，and they swim about in the sea.Most of them are eaten up by fishes；but those that escape settle down on the sea-bottom，and begin to form their shells.
11.Fishermen scrape the oysters off the sea-bottom by means of a dredge，which is a bag-shaped net with an iron rim.Then they are sent to London and to other large towns，to be sold for food.Oysters are a very good food，and they are very easy todigest②，but they are rather dear.
12.A great many oysters are also found along the coasts of North America，and some of these are now put into barrels and sent to this country alive.The oyster will live for two or three weeks after it is taken out of the sea，if it is kept wet with sea-water.
SUMMARY
The oyster has two hard shells which are joined together by a hinge.With the larger of these shells it fastens itself to rocks or to the sea-bottom.The oyster gets its food out of the sea-water.It breathes like a fish by sucking air out of the water.In summer the oyster lays its tiny eggs，many of which are eaten up by fish.Those that remain settle down on the sea-bottom and form their shells.When two years old，they are ready to be dredged off the sea-bottom and used as food.From a kind of oyster pearls are got.
①Thames，a large river in the south of England.
②Digest，dissolve food in the stomach.
【中文阅读】
1．牡蛎是一种贝类（shell-f i sh），意思是“带壳的鱼”。但它不是真正的鱼，跟比目鱼和鲱鱼不一样。所有真正的鱼都有一条脊椎骨，借助尾巴和鳍的帮助，在海里游来游去。①2．但是牡蛎没有脊椎骨，其实，牡蛎连一点儿骨头都没有。它柔软的身体躺在两片坚硬的甲壳（）之间，让这两片甲壳来保护。
3．这两片甲壳，一片大，一片小；牡蛎用那片大甲壳，把自己固定在岩石上，或者海底的泥地上，就在这些地方生活。
4．两片甲壳由一条蝶铰相连；②牡蛎还有一块强壮的肉，学名叫“闭壳肌”，用它来闭合两片甲壳。如果把一只牡蛎从水里捞出来，你会发现牡蛎的两片壳闭合得非常紧，掰都掰不开。③5．牡蛎一般要用刀子撬开；但是如果放进开水里，马上就会死掉，贝壳也就很轻易地打开了。请看空牡蛎壳的内部，你会看见一个小小的空洞，肌肉就是在这儿附着在壳上的。
6．贝壳的内部，像珍珠一样闪闪发亮。其实，牡蛎中有一种，就是能制造珍珠的。牡蛎的贝壳和珍珠，都是用溶解在海水里的物质制造的。④7．牡蛎有一张小口，一个胃，还有其他的器官。牡蛎的呼吸方式跟鱼很像，也是用鳃从海水中吸进空气的。牡蛎还从海水中得到食物。
8．牡蛎把海水吸进口中，又让海水从鳃流出来，但是海水中的任何小生物都被抓住，吞了下去，进了牡蛎的胃。
9．质量最好的牡蛎，出产在泰晤士河口，英吉利海峡，法国海岸。⑤10．牡蛎在夏季产卵，一次能产数百万粒，不比大头针的针尖更大。（孵化出的幼体）在水里到处游逛。大多数的卵都被鱼吃掉了，但逃脱的幼体就在海底安家，开始长自己的贝壳。
11．渔民用一种“捞网”把牡蛎从海底刮下来。捞网也叫“挖泥机”
（dredge），是一种袋子形状的网，带着一个铁耙子。然后，渔民会把捕捞的牡蛎，送到伦敦和其他大城市，当做食品出售。牡蛎是非常美味的食品，很容易消化，但相当贵。⑥12．沿着北美海岸，也能找到很多牡蛎，有一些也放进大桶，活着运到英国。牡蛎从海里捞出来，浸在海水里，还能活两三个星期。⑦译注①鱼属于“脊索动物门”“鱼纲”，牡蛎属于“软体动物门”“瓣鳃纲”，关系那是相当地远！牡蛎的另一个汉语名字是“生蚝”。
②蝶铰的原文是hinge，指牡蛎等贝类两片甲壳连在一起的部分。
③贝壳的主要成分是碳酸钙和磷酸钙，牡蛎有一个产生贝壳的器官，叫“外套膜”。
④这种牡蛎一般叫“珠母贝”。当有异物进入外套膜和贝壳之间的时候，珠母贝会用形成贝壳的“珍珠质”，层层包裹异物，最后就产生了珍珠。牡蛎并不直接从海水中提取矿物质来制造贝壳和珍珠，而是用自己食物中的矿物质。20世纪初，出现了人工养殖的珍珠，目前养殖珍珠的市场已经远远超过了天然珍珠。
⑤中国广东的珠江口沙井蚝，是国内最有名的牡蛎种类之一。
⑥目前国产牡蛎的价格，1市斤一般在50-80元，进口的品种还要贵一些。
⑦现在，因为过度捕捞和海水污染的缘故，野生牡蛎的数量锐减。2011年的研究发现，课文里提到的北美、欧洲，还有澳大利亚地区的牡蛎数量居然减少了85%。如果这个势头再继续下去，读者今后能不能吃到牡蛎，恐怕都会成问题了。人们正在设法限制牡蛎捕捞，并且大力发展养殖业，以挽救这道人间美食。
THE CRUSTY CRAB