Which one of the following statements is incorrect ?

Options

A. In cockroaches and prawns excretion of waste material occurs through malpighian tubules.
B. In ctenophores, locomotion is mediated by comb plates
C. In fasciola flame cells take part in excretion
D. Earthworm are hermaphrodites and yet cross fertilization take place among them .

Answer

To determine which statement is incorrect, we will analyze each option provided in the question step by step.

### Step-by-Step Solution:

1. **Analyze the First Statement**:
- The statement claims that in cockroaches and prawns, excretion of waste material occurs through Malpighian tubules.
- **Cockroaches**: This is correct; they do excrete waste through Malpighian tubules.
- **Prawns**: This is incorrect; prawns excrete waste through green glands, not Malpighian tubules.
- **Conclusion**: This statement is incorrect.

2. **Analyze the Second Statement**:
- The statement claims that locomotion in Ctenophores is mediated by comb plates.
- This is correct; Ctenophores use comb plates (ctenes) for locomotion.
- **Conclusion**: This statement is correct.

3. **Analyze the Third Statement**:
- The statement claims that in Fasciola, flame cells take part in excretion.
- This is correct; flame cells are involved in excretion in Fasciola (liver flukes).
- **Conclusion**: This statement is correct.

4. **Analyze the Fourth Statement**:
- The statement claims that earthworms are hermaphrodites and yet cross-fertilization takes place among them.
- This is correct; earthworms have both male and female reproductive organs but still engage in cross-fertilization.
- **Conclusion**: This statement is correct.

### Final Conclusion:
The only incorrect statement among the options is the **first statement** regarding the excretion process in prawns.