Atrium of Periplaneta is a

Options

A. tracheal ring
B. tube of trachea
C. cavity below spiracle
D. fluid filled in trachea

Answer

### Step-by-Step Solution:

1. **Understanding the Term "Periplaneta":**
- Periplaneta refers to the genus of cockroaches, specifically the American cockroach.

2. **Defining "Atrium":**
- In the context of Periplaneta (cockroach), the atrium is a specific structure related to its respiratory system.

3. **Cockroach Respiratory System Overview:**
- Cockroaches do not have lungs like mammals. Instead, they breathe through a network of tubes called trachea.

4. **Function of Trachea:**
- The trachea is a system of tubes that transport air directly to the tissues of the cockroach.

5. **Role of Spiracles:**
- Air enters the cockroach's body through openings known as spiracles. There are typically 10 pairs of spiracles located on the sides of the cockroach's body.

6. **Structure of Spiracles:**
- Each spiracle is bordered by a chitinous plate and is guarded by bristles to prevent the entry of dust and other particles.

7. **Mechanism of Air Entry:**
- The opening and closing of spiracles are controlled by sphincter muscles, which help regulate air intake and prevent water loss.

8. **Location of the Atrium:**
- The atrium is located just below the spiracles. It serves as a chamber where the air collects before entering the trachea.

9. **Air Flow from Atrium to Trachea:**
- Once air enters the atrium, it flows into the trachea, which then branches into smaller tubes called tracheoles, delivering oxygen to the cells of the cockroach.

10. **Conclusion:**
- The atrium of Periplaneta is correctly identified as the cavity located below the spiracles, where air collects before entering the tracheal system.

### Final Answer:
The atrium of Periplaneta is a **cavity below the spiracles**.