Amnion membrane is absent upto amphibians,

Answer

**Step-by-Step Solution:**

1. **Understanding the Amnion Membrane:**
- The amnion is a protective membrane that surrounds the embryo in amniotes (mammals, reptiles, and birds).
- Its primary function is to provide a cushioning effect and protect the embryo from mechanical shocks.

2. **Presence of Amnion in Different Groups:**
- The amnion membrane is present in mammals and some reptiles and birds, which undergo internal fertilization.
- In contrast, amphibians and fish primarily exhibit external fertilization, where eggs are fertilized outside the female's body.

3. **Absence of Amnion in Amphibians:**
- In amphibians, the absence of the amnion is due to their reproductive strategy of external fertilization.
- When amphibians lay eggs in water, the eggs are surrounded by a gelatinous coating that serves a protective function similar to that of the amnion.

4. **Role of Gelatinous Coating:**
- The gelatinous coating provides protection against physical shocks and environmental factors.
- This coating, combined with the aquatic environment, helps safeguard the developing embryos from damage.

5. **Conclusion:**
- The statement that the amnion membrane is absent in amphibians is true because their eggs are protected by a gelatinous substance in an aquatic environment, fulfilling a similar role to that of the amnion in amniotes.

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