In cockroach, the malpighian tubules constitute the excretory system.

Answer

### Step-by-Step Solution:

1. **Introduction to the Excretory System in Cockroach**:
- The excretory system in cockroaches is primarily constituted by structures known as Malpighian tubules. These tubules play a crucial role in the elimination of waste products from the body.

2. **Understanding the Anatomy of the Cockroach**:
- To comprehend the function of Malpighian tubules, it is essential to understand the overall anatomy of the cockroach, particularly the digestive system, as the tubules are closely associated with it.

3. **Elementary Canal Structure**:
- The elementary canal of the cockroach consists of three main parts: the foregut, midgut, and hindgut.
- **Foregut**: Includes the mouth, salivary glands, and crop.
- **Midgut**: Contains the gizzard and is where most digestion occurs.
- **Hindgut**: Comprises the ileum, colon, rectum, and anus.

4. **Location of Malpighian Tubules**:
- The Malpighian tubules are located at the junction of the midgut and hindgut. They are thread-like structures that can number between 100 to 150 in a single cockroach.

5. **Appearance and Function**:
- These tubules are yellow, filamentous structures that extend into the hemolymph (the blood-like fluid in cockroaches). Their primary function is to filter waste from the hemolymph and excrete it.

6. **Excretion Process**:
- The Malpighian tubules absorb waste materials from the hemolymph and convert them into uric acid, which is then passed into the hindgut for elimination from the body.

7. **Conclusion**:
- In summary, the Malpighian tubules are vital excretory structures in cockroaches, facilitating the removal of metabolic waste and maintaining homeostasis within the organism.

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