Consider the lobster（龙虾）. Other than living on Earth, we don't have a lot in common with these arthropods（节肢动物(的)）. The group of animals includes everything from spiders to insects to crustaceans（甲壳类动物）, like these guys. 80% of all known animal species are arthropods. They're noted（注意） for having segmented（分割） bodies, jointed（把〔肉〕切成大块） legs, and stiff（硬的） exoskeletons（[昆] 外骨骼）. If you ask me, the most amazing difference between you and me and this lobster isn't immediately obvious.

  Let me show you. Right here, the poop chute, or more accurately（精确地）, the dorsal（背的） intestine（肠）. Now, if you've ever eaten lobster, shrimp, or crawfish, you've probably just thrown this thing away. But this gross（总的） little tube holds more than just lobster（龙虾） poop. It tells a special story of one event hundreds of millions of years ago that changed the course of your body. In 1822, a French naturalist（ 自然主义者） by the name of Joffre Centilier cut open a lobster（龙虾） and noticed that its arthropod（节肢动物(的)） anatomy was essentially a mirror image of our own, one what's called the dorsovetral axis（轴）.

  And old Joffre never did figure（ 认为） out why, but his observation（观察） was right on. Animals like us have our guts（内脏） in circulatory（循环的） system on our belly side and our nerve（神经） cords along our backs.