Blastopore is the opening of:

Options

A. Blastocoel
B. Archenteron
C. Coelenteron
D. Gastrocoel

Answer

### Step-by-Step Solution:

1. **Understanding the Concept of Blastopore**:
The blastopore is an important structure that forms during the early stages of embryonic development in animals.

2. **Formation of Blastopore**:
The blastopore arises from the blastula stage, which consists of 60 to 70 cells. During this stage, a fluid-filled cavity called the blastocoel is present.

3. **Transition from Blastula to Gastrula**:
As development progresses, the blastula undergoes a process called gastrulation, leading to the formation of the gastrula, which contains more than 15,000 cells.

4. **Structure of Gastrula**:
In the gastrula, two primary germ layers are formed: the endoderm and ectoderm. The gastrula also has a central cavity known as the archenteron.

5. **Role of Archenteron**:
The archenteron serves as a pathway for cells to migrate and differentiate into various tissues. The opening through which the archenteron begins is referred to as the blastopore.

6. **Conclusion**:
Therefore, the blastopore is the opening of the archenteron in the gastrula stage of embryonic development.

### Final Answer:
**Blastopore is the opening of the archenteron.**

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