1. When we talk about ears, we usually mean the oddly wrinkled appendages on the sides of our heads. 2. We are aware that at the end of the central hole in this outer ear there is something called the middle ear, with an eardrum and a few little bones. Even deeper lies the inner ear, the organ with which we hear. 3. Animals such as dogs and cats also have conspicuous outer ears, but few of us probably ever stopped to think whether there might be such a thing as a middle and inner ear beneath those pointed tips. Yet, we know very well that these animals hear. 4. Birds are even more mysterious, because here we do not even see an outer ear. The same is true to still a larger degree of such animals as frogs and fishes, although in the frog we can at least see an eardrum. 5. Again, at one time or another, you may have found that all such animals hear. Hunters know that birds are attracted by artificial calls, and fishermen emphasize that you should be as quiet as possible if you dont want to go home empty handed. And if you ever hunted frogs in your childhood, you know how softly you had to tread! Moreover, it seems absurd that birds should sing and frogs croak, if they could not even hear their own voices. 6. By direct observations and many experiments, biologists have discovered that practically all animals have some sense of hearing or vibration. Earthworms feel vibrations in the soil, fish can be trained to respond to certain tones, male mosquitoes are attracted by the sound of the female, and frogs will respond to a tape recording of their own voices. 7. The inner ear is composed of delicate membranes which bear dense patches of specialized cells called maculae. Each of these collections of cells can carry a message to the brain. What message is carried by a macula depends upon how it is affected. The message which is carried is not, however, always connected with the hearing sense. For instance, a certain kind of tadpole can tell the depth of the water it is swimming in by the pitch of a tone which is produced by its own lungs. 8. In the human and all other mammals, the macula has developed into an organ which can easily be seen. This organ is called the cochlea. This spiral shaped organ contains the macula itself and it is called organ of Corti after its discoverer. If you have ever seen a snail shell, you know how a cochlea looks. 9. When sound waves enter the cochlea, which is really a tube coiled around, they set a membrane into a back and forth motion and cause a new wave. This is something like the way in which high and low sounds are produced by a flute or whistle. The high sounds are produced when the air is prevented by the holes from going through, while the low sounds are produced by allowing more of the air to pass. All this is what produces the differences between high and low sounds. The loudness of a sound is evidently produced by how much the membrane is cause to move. 10. Whether or not hearing is really produced in all animals by the effect of pressure is not definitely known by scientists as yet. We do know, however, that nature has set up some very delicate hearing mechanisms for its creatures. Scientists must explore much further for more knowledge about how animals use their ears.
高考语法习题之主谓一致
体坛英语资讯:Italy join Netherlands in last eight after beating France 2-0
体坛英语资讯:Zheng Jie knocks out top-seeded Ana Ivanovic at Wimbledon
少儿双语小故事:顽皮的弟弟
体坛英语资讯:Croatia bullish, Germany relieved at Euro 2008
体坛英语资讯:Milwaukee Bucks trade Yi to Nets
高二英语教案 Unit 2 No smoking, please! --1
体坛英语资讯:Germany edges into Euro 2008 final after defeating Turkey by 3-2
体坛英语资讯:Federer, Safin, Nadal reach Wimbledon semifinal
体坛英语资讯:Venus, Sharapova go through at Wimbledon
体坛英语资讯:Hansen denied berth in 200m breaststroke
高考语法习题之形容词和副词
体坛英语资讯:Venus beats Serena for fifth title at Wimbledon
体坛英语资讯:Hamilton rules at home in rain
体坛英语资讯:Nadal outlasts Federer in 5 sets to win 1st Wimbledon title
体坛英语资讯:Zhao Ruirui ready to put bad luck behind her
高二英语教案 Unit 1 Disneyland -1
体坛英语资讯:Cuban Robles sets 110m hurdles new world record at Golden Spike
少儿双语故事:愚蠢的小妖精
少儿双语故事:作为一个孩子是不容易的
体坛英语资讯:Dutch advance, Italy, France on brink of elimination
高考语法复习之分词
高考语法习题之助动词
体坛英语资讯:China announces 598 Olympic homestays in Beijing
体坛英语资讯:Ricco soars high for 2nd stage win
少儿双语小故事:巨人杰弗瑞
体坛英语资讯:Spain makes Euro 2008 final on 3-0 victory over Russia
体坛英语资讯:Win or lose, Jiang confident Williams will be shocked
体坛英语资讯:Russia through, champions bow out without win at Euro 2008
体坛英语资讯:Chelsea rejects Inters bid for Lampard