D: What's the difference between a hard-shelled blue crab and a soft-shelled blue crab?
D: 你知道软壳青蟹和硬壳青蟹有什么区别吗？
Y: Is this a trick question?
Y: 这个问题很难吗？
D: I'll give you a hent. It has to do with the crab’s skeletal system.
D: 我来给你个提示。 这与螃蟹的骨骼系统是紧密相关的。
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?
Y: 骨骼系统？ 哦，我大概懂了。就像是其它的甲壳类动物一样，螃蟹会定期的褪壳。 也就是说，螃蟹褪掉原有的硬壳再重新长出新壳。 但问题是，我想不明白这怎么就和骨骼系统扯上了关系。
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.
D: 那就由我来告诉你吧。 当一只青蟹褪掉了它的硬壳（也就是它的外骨骼）之后，新长出的壳要等上大概一个星期才能变硬。 在壳变硬之前，外面的那层“壳”太软太韧了，以致于无法进行正常的肌肉收缩，在新壳变硬之时还要再进行一次。 而且，不知为何，青蟹在这种情况下还是能到处爬来爬去的，即使是刚刚褪壳的时候也是如此。
Y: How is that possible?
Y: 这怎么可能呢？
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.
D: 使用铃静力骨架就可以了！ 许多种动物，比如说蠕虫，它们一生都是靠铃静力骨架支撑下来的。 这也就是说，肌肉的收缩通过不可压缩铃被传送到了身体各部分。 青蟹刚刚褪壳的时候，体内的铃静压力陡然飚到很高，这使得青蟹可以利用压力来使肌肉活动。 青蟹的铃静力骨架并不是特别出众，真正出众的是青蟹在外骨骼和铃静力骨架之间出众的交替使用能力。 科学家们猜测，蟹并不是唯一一种此类动物，接下来，科学家们将会研究更多褪壳生物的骨骼系统。
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