英語聽力文摘 神奇的蟹

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Amazing Crabs

D: What's the difference between a hard-shelled blue crab and a soft-shelled blue crab?

Y: Is this a trick question?

D: I'll give you a hent. It has to do with the crab’s skeletal system.

Y: Skeletal system? You got me there, I know that like other crustaceans, periodicallymolt. That is, the crab sheds its hard shell and forms a new one. But I don't have a clue as to what that means about the skeletal system?

D: Well, I'll tell you. When a blue crab sheds its hard shell, its exoskeleton, it has to wait about a week for the new shell to harden. Before that happens, this outer layer of tissue is too soft and flexible to transmit muscle contractions as it did, and will do again when the crab’s new shell hardens. And yet these creatures are somehow still able to move about, even immediately after molting.

Y: How is that possible?

D: It's possible using a hydrostatic skeleton. Many animals, such as worms, rely on hydrostatic skeletons all their lives. What this means is that muscle contractions are transmitted through an incompressible fluid. Immediately after molting, the hydrostatic pressure inside crabs jumps significantly higher, allowing the crabs to use this pressure to move their muscles. While a hydrostatic skeleton isn’t so remarkable in itself, what is remarkable is that the crab alternates between using the two kinds of skeletons. Scientists suspect that crabs probably aren’t alone in this feat and plan to investigate the skeletal systems of other creatures that molt.

神奇的蟹

D: 你知道軟殼青蟹和硬殼青蟹有什么區(qū)別嗎?

Y: 這個問題很難嗎?

D: 我來給你個提示。這與螃蟹的骨骼系統(tǒng)是緊密相關(guān)的。

Y: 骨骼系統(tǒng)?哦，我大概懂了。就像是其它的甲殼類動物一樣，螃蟹會定期的褪殼。也就是說，螃蟹褪掉原有的硬殼再重新長出新殼。但問題是，我想不明白這怎么就和骨骼系統(tǒng)扯上了關(guān)系。

D: 那就由我來告訴你吧。當(dāng)一只青蟹褪掉了它的硬殼(也就是它的外骨骼)之后，新長出的殼要等上大概一個星期才能變硬。在殼變硬之前，外面的那層“殼”太軟太韌了，以致于無法進(jìn)行正常的肌肉收縮。在新殼變硬之時還要再進(jìn)行一次。而且，不知為何，青蟹在這種情況下還是能到處爬來爬去的，即使是剛剛褪殼的時候也是如此。

Y: 這怎么可能呢?

D: 使用鈴靜力骨架就可以了!許多種動物，比如說蠕蟲，它們一生都是靠鈴靜力骨架支撐下來的。這也就是說，肌肉的收縮通過不可壓縮鈴被傳送到了身體各部分。青蟹剛剛褪殼的時候，體內(nèi)的鈴靜壓力陡然飚到很高，這使得青蟹可以利用壓力來使肌肉活動。青蟹的鈴靜力骨架并不是特別出眾，真正出眾的是青蟹在外骨骼和鈴靜力骨架之間出眾的交替使用能力。科學(xué)家們猜測，蟹并不是唯一一種此類動物，接下來，科學(xué)家們將會研究更多褪殼生物的骨骼系統(tǒng)。

Notes: trick question 欺騙性問題，假如有人問一個“欺騙性問題”，那就是說他問了一個非常難回答的問題，比如說其中暗藏難點(diǎn)或是顯而易見并非正確的問題。