What external changes are visible after the last moult of a cockroach nymph?

Options

A. Mandibles become harder
B. Anal cerci develop
C. Both fore wings and hind wings develop
D. Labium develops

Answer

**Step-by-Step Solution:**

1. **Understanding the Life Cycle of Cockroaches:**
- Cockroaches undergo a process called hemimetabolism, which involves several molts throughout their life cycle. This means that they shed their exoskeleton multiple times as they grow.

2. **Molting Process:**
- A cockroach nymph will molt approximately 13 times before reaching adulthood. Each molt brings the nymph closer in appearance to an adult cockroach.

3. **Development of Wings:**
- In the second last nymphal stage, the nymph begins to develop wing pads. This is a crucial change that indicates the nymph is nearing adulthood.

4. **Last Molt:**
- After the final molt, the nymph transforms into an adult cockroach. This final molt is significant as it brings about the most noticeable external changes.

5. **Visible Changes After the Last Molt:**
- The most prominent external changes visible after the last molt are the development of both forewings and hindwings. This is the key differentiation between the nymph and the adult cockroach.

6. **Conclusion:**
- Therefore, the external changes that are visible after the last molt of a cockroach nymph include the presence of fully developed wings.

**Final Answer:**
The external changes visible after the last molt of a cockroach nymph are the development of both forewings and hindwings.

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