The retinulae of houseflies differ from cockroach in the 

Options

A. presence of retinulae just below vitrillae and absence of secondary pigment cells
B. presence of retinulae deep below vitrillae and presence of primary pigment cells
C. presence of retinulae just below vitrillae and presence of secondary pigment cells
D. none

Answer

To answer the question regarding how the retinulae of houseflies differ from those of cockroaches, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure**: The retinulae are the light-sensitive cells found in the compound eyes of insects. They play a crucial role in the visual system of these organisms.

2. **Identify the Organisms**: We are comparing the retinulae of houseflies (Musca domestica) and cockroaches (Blattella germanica).

3. **Examine the Options**: The question provides four options regarding the differences in retinulae:
- Presence of the retinula just below the vitrella and absence of the secondary pigment cells.
- Presence of the retinula deep below the vitrella and presence of primary pigment cells.
- Presence of the retinula just below the vitrella and presence of secondary pigment cells.
- None of the above.

4. **Analyze the Retinula Position**:
- In houseflies, the retinula is located just below the vitrella (the transparent layer of the eye).
- In cockroaches, the retinula is located deeper within the eye structure.

5. **Consider the Pigment Cells**:
- Houseflies have secondary pigment cells that help in the functioning of their eyes.
- Cockroaches also have pigment cells, but the type and arrangement may differ.

6. **Eliminate Incorrect Options**:
- The first option is incorrect because it states the absence of secondary pigment cells, which is not true for houseflies.
- The second option is incorrect because it states the retinula is deep below the vitrella, which is not accurate for houseflies.
- The fourth option (none) can be eliminated since there is a difference.

7. **Select the Correct Option**:
- The third option is correct: "Presence of the retinula just below the vitrella and presence of secondary pigment cells." This accurately describes the retinulae of houseflies compared to cockroaches.

### Final Answer:
The retinulae of houseflies differ from those of cockroaches in the presence of the retinula just below the vitrella and the presence of secondary pigment cells.

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