中胚叶

例句：

1. 1. The plant's growth is closely related to the development of its vascular system.
   植物的生长与其血管系统的发育密切相关。
2. 2. During embryonic development, the cells in the mid-layer are responsible for forming the body's internal organs.
   在胚胎发育过程中，中层细胞负责形成身体的内部器官。
3. 3.Researchers have discovered that the mid-layer plays a crucial role in the development of the nervous system.
   研究人员发现，中层在神经系统的发展中起着关键作用。