vestigial

蛇类体内仍保留着退化的后肢骨骼。

Snakes still possess ___vestigial bones from their ancestral hind legs.

人类的阑尾被认为是一个退化的器官。

The human appendix is considered a ___vestigial organ.

某些洞穴鱼的眼睛已经退化成无用的结构。

Some cave fish have ___vestigial eyes that serve no purpose.