pit membrane

例句：

1. 1. The surgeon removed the tumor from the patient's abdomen with a sharp knife.
   外科医生用一把锋利的刀从病人腹部切除了肿瘤。
2. 2. The scientist studied the structure of the pit membrane in detail.
   科学家详细研究了囊膜的结构。
3. 3. The researcher found that the pit membrane plays an important role in maintaining the balance of body fluids.
   研究者发现囊膜在维持体液平衡方面起着重要作用。