From a central feather vane sprout hundreds of filaments called barbs.

从中央羽毛叶片萌芽数以百计的长丝所谓钩。

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Only after stage 4 could additional feather variations evolve, including the many specializations we see at stage 5, such as the asymmetrical vane of a flight feather.

一旦演化到阶段4之后，其他各种不同的羽毛才能够演化出来，包括我们在阶段5看到的各种特化羽毛，例如飞羽的不对称羽片。

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