1. 发育中有变态现象:

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/fa3a908d-6f99-4463-b5cd-e1c92fe547cc/Untitled.png

  1. 脊椎分成四部分:颈椎、躯椎、荐椎、尾椎

https://s3-us-west-2.amazonaws.com/secure.notion-static.com/1f88c7e8-8adf-40c4-a1e4-c7437e6f4348/Untitled.png

  1. 开始出现中耳,能将声音传入内耳发生听觉

  2. 卵生,体外受精,不具钙质的卵壳。