| {{B}}
The whale is a mammal (哺乳动物) - warm-blooded, air-breathing, giving birth to its young alive, sucking them - and, like all mammals, originated on land. There are many signs of this. {{U}}(51) {{/U}} front flippers (鳍肢), used for steering and stability, are traces of feet. Immense strength is built into the great body of the big whales, and in fact most of a whale's body is one gigantic muscle. The blue whale's pulling {{U}}(52) {{/U}} has been estimated at 400 horsepower. One specimen was reported to have {{U}}(53) {{/U}} a whaling vessel for seven hours at the {{U}}(54) {{/U}} of eight knots. An enraged whale will attack a ship. A famous {{U}}(55) {{/U}} of this was the fate of whaler Essex, which was sunk {{U}}(56) {{/U}} the coast of South America early in the last century. More recently, steel ships have had their plates buckled (扭曲变形)in the same way. Sperm whales were known to {{U}}(57) {{/U}} the old-time whaleboats in their jaws and crush them. The greatest mystery of whales is their diving ability. The sperm whale can {{U}}(58) {{/U}} the bottom for his favorite food, the octopus (章鱼). {{U}}(59) {{/U}} that search he is known to go as far down as 3,200 feet, where the pressure is 1,400 pounds, to the square inch. Doing {{U}}(60) {{/U}} he will remain submerged (水下的) as long as one hour. Two feats (绝技) are involved in this: storing up enough {{U}}(61) {{/U}} (all whales are air-breathed) and withstanding the great change in pressure. Just {{U}}(62) {{/U}} he does it scientists have not determined. It is believed that some of the oxygen is stored in a special system of blood vessels, rather than just held in the lungs. And {{U}}(63) {{/U}} is believed that a special kind of oil in his head is some sort of compensating mechanism that automatically adjusts the internal pressure of his body. But {{U}}(64) {{/U}} you can't bring a live whale into the laboratory for study, no one {{U}}(65) {{/U}} just how these things work. |