In cockroaches, the flow of haemolymph is:

Options

A. Heart `to` Head haemocoel `to` Perivisceral sinus `to` Pericardial sinus `to` Ostia `to` Heart
B. Heart `to` Pericardial sinus `to` head haemocoel `to` Perivisceral sinus `to` Ostia `to` Heart
C. Heart `to` Head haemocoel `to` Perivisceral sinus `to` Ostia `to` Pericardial sinus `to` Ostia
D. Heart `to` Ostia `to` Perivisceral sinus `to` Pericardial sinus `to` Head haemocoel `to` Ostia

Answer

To understand the flow of haemolymph in cockroaches, we need to analyze the circulatory system of these insects. Cockroaches have an open circulatory system, which means that their blood (haemolymph) is not confined to blood vessels but flows freely within cavities.

### Step-by-Step Solution:

1. **Identify the Components of the Circulatory System**:
- The main components involved in the flow of haemolymph in cockroaches include the heart, hemocoel, perivisceral sinus, pericardial sinus, and ostia.

2. **Flow of Haemolymph**:
- The flow of haemolymph starts at the **heart**. The heart pumps the haemolymph into the **hemocoel**, which is the primary body cavity in insects.

3. **Movement to Sinuses**:
- From the hemocoel, the haemolymph moves into the **perivisceral sinus**. This sinus is a large fluid-filled cavity that surrounds the internal organs.

4. **Pericardial Sinus**:
- After the perivisceral sinus, the haemolymph enters the **pericardial sinus**. This sinus is located around the heart and is formed by the impressions of the pericardial sac.

5. **Return to the Heart**:
- The haemolymph then flows through the **ostia**, which are openings in the heart that allow the haemolymph to re-enter the heart. The ostia function as valves that prevent backflow.

6. **Cycle Completion**:
- The cycle completes as the haemolymph is pumped back into the heart, and the process repeats.

### Conclusion:
The correct flow of haemolymph in cockroaches can be summarized as:
**Heart → Hemocoel → Perivisceral Sinus → Pericardial Sinus → Ostia → Heart**.

Thus, the correct answer is the first option provided in the question.