这样的话,至少在一只蠕虫身上出现了在中央神经系统中腹部与背部的发育的分离,并且他主张同样发育上的分离早在Urbilateria时期就已经出现了.
Thus the development of front and back has been decoupled from the development of a central nervous system in one worm at least, and he argues that the same separation may have existed in Urbilateria.
驼背鲸有一个较小的背鳍，大约是背部三分之二接近尾部的中央。
The humpback has a small dorsal fin located towards the tail flukes about two-thirds of the way down its back.
驼背鲸有一个较小的背鳍，大约是背部三分之二接近尾部的中央。
The humpback has a small dorsal fin located towards the tail flukes about two-thirds of the way down its back.
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