In Hydra, nematocysts occur only in

Options

A. Epidermis
B. Gastrodermis
C. Mesodermis
D. Endodermis

Answer

To answer the question "In Hydra, nematocysts occur only in", we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Structure of Hydra**:
- Hydra is a member of the phylum Cnidaria. It has a simple body structure consisting of two main layers: the outer epidermis (ectodermally derived) and the inner gastrodermis (endodermally derived).

2. **Identify the Types of Cells in Hydra**:
- The epidermis contains various types of cells, including epithelial muscular cells and specialized cells called nematocysts (also known as cnidocytes).
- The gastrodermis contains nutritive muscular cells and gland cells, but it does not contain nematocysts.

3. **Locate the Nematocysts**:
- Nematocysts are specialized cells that are primarily found in the epidermis of Hydra. They play important roles in anchorage, defense, and capturing prey.

4. **Conclusion**:
- Since nematocysts are present only in the epidermis of Hydra and not in the gastrodermis, we conclude that the correct answer to the question is that nematocysts occur only in the epidermis.

### Final Answer:
- **Nematocysts occur only in the epidermis of Hydra.**