Name the stage at which zona pellucida envelop disintegrates

Explanation

### Step-by-Step Solution:

1. **Understanding Zona Pellucida**:
- The zona pellucida is a thick, transparent membrane that surrounds the mammalian ovum (egg) before implantation. It plays a crucial role in fertilization and early embryonic development.

2. **Identifying the Stage of Disintegration**:
- The question specifically asks for the stage at which the zona pellucida disintegrates. This occurs during the development of the embryo.

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