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SSS 2009-07-10

时间:2010-05-18 03:13来源:互联网 提供网友:mark@li   字体: [ ]
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    (单词翻译:双击或拖选)

This is Scientific American's 60-Second Science, I'm Cynthia Graber. This will just take a minute.

 

It sounds like the title to a Rudyard Kipling tale: how the turtle got its shell. But it’s actually a question that has puzzled scientists. After all, no other animal, living or extinct, has a similarly constructed bony shield surrounding its body. Scientists had thought that, over evolutionary1 time, small bony plates fused with the animal’s skin. But a new study published July 10th in the journal Science offers a different pathway.

 

In most animals the shoulder blades lie outside the ribs2. Not so with turtles. And there’s no intermediate evolutionary form in which the shoulder blades lie beneath ribs. So researchers in Japan compared chicken, mouse and Chinese soft-shelled turtle embryos3 at different stages of development. They show that initially4 the embryos develop along the same pathways. But the turtle takes a turn.

 

As it develops, part of its body folds in on itself. Shoulder blades get folded within the ribs. The ribs stay connected, but new connections also develop between bone and muscles. Then the shell starts to develop as the ribs fuse together and encase the shoulder blades. Not as droll5 perhaps as a “Just So” story. But more fascinating for being true.

 

Thanks for the minute, for Scientific American's 60-Second Science, I'm Cynthia Graber.
 


点击收听单词发音收听单词发音  

1 evolutionary Ctqz7m     
adj.进化的;演化的,演变的;[生]进化论的
参考例句:
  • Life has its own evolutionary process.生命有其自身的进化过程。
  • These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。
2 ribs 24fc137444401001077773555802b280     
n.肋骨( rib的名词复数 );(船或屋顶等的)肋拱;肋骨状的东西;(织物的)凸条花纹
参考例句:
  • He suffered cracked ribs and bruising. 他断了肋骨还有挫伤。
  • Make a small incision below the ribs. 在肋骨下方切开一个小口。
3 embryos 0e62a67414ef42288b74539e591aa30a     
n.晶胚;胚,胚胎( embryo的名词复数 )
参考例句:
  • Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段,而且其行为象胚。 来自辞典例句
  • Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句
4 initially 273xZ     
adv.最初,开始
参考例句:
  • The ban was initially opposed by the US.这一禁令首先遭到美国的反对。
  • Feathers initially developed from insect scales.羽毛最初由昆虫的翅瓣演化而来。
5 droll J8Tye     
adj.古怪的,好笑的
参考例句:
  • The band have a droll sense of humour.这个乐队有一种滑稽古怪的幽默感。
  • He looked at her with a droll sort of awakening.他用一种古怪的如梦方醒的神情看着她.
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