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Whales, like dolphins, belong to a group of mammals(哺乳动物)called “cetaceans”.This name comes from a Latin word meaning “large sea animal”.There are at least seventy-five kinds of cetaceans.Scientists divide the various kinds into two major groups-baleen whales, which do not have teeth, and toothed whales, which have teeth.
Whales have the same basic shape as fish, but they differ from fish in many ways.The most noticeable difference is the tail.Fish have vertical(垂直的)tail fins(鳍), but whales have horizontal tail fins.Fish breathe by means of gills(腮), while whales have lungs(肺)and must come to the surface to breathe.But they can hold their breath for long periods.
Like other mammals, whales give birth to live young and feed them with milk produced by the mother’s body.Most fish, however, lay eggs and do not feed their young.Whales are also warm-blooded-that is, their body temperature remains about the same all the time.Almost all fish are cold-blooded.Their body temperature changes with changes in the temperature of the water.
Whales have a highly developed brain and they are highly advanced life forms.They sing to their young, engage in complex family relationships, and their communication skills are fine.
In December 2005, a whale, after being rescued from fishing nets, didn’t just swim back to deep water.It hung around and touched each of the divers with its mouth.“Knowing that it was free, it stopped about a foot away from me, pushed me around a little bit and had some fun,” said dive master James Moskito.He thought it was “one of the most fantastic moments” of his life.
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