Hydra receives stimuli through
(a) Nerve cells
(b) Nerve net
(c) Sensory cells
(d) Nematocysts

Options

A. Nerve cells
B. Nerve net
C. Sensory cells
D. Nematocysts.

Answer

To solve the question "Hydra receives stimuli through," we will analyze each option provided and determine which one is correct based on the characteristics of Hydra.

### Step-by-Step Solution:

1. **Understanding Hydra's Structure**:
- Hydra is a simple aquatic organism belonging to the phylum Cnidaria. It has a basic body structure that includes a gastrovascular cavity and specialized cells.

2. **Evaluating Option (a) Nerve cells**:
- Nerve cells, or neurons, are specialized cells that transmit signals in more complex organisms. Hydra does not have a centralized nervous system or true nerve cells like higher animals.

3. **Evaluating Option (b) Nerve net**:
- While some cnidarians possess a nerve net, Hydra specifically does not have a true nerve net structure. Instead, it has a more primitive arrangement of nerve cells.

4. **Evaluating Option (c) Sensory cells**:
- Hydra contains specialized sensory cells that are responsible for detecting stimuli. These sensory cells are located in the gastrodermis and can respond to environmental changes, such as the presence of prey.

5. **Evaluating Option (d) Nematocysts**:
- Nematocysts are specialized stinging cells found in cnidarians, including Hydra. They are used for capturing prey and defense, but they do not function in receiving stimuli.

6. **Conclusion**:
- Based on the evaluation, the correct answer is **(c) Sensory cells**. Hydra receives stimuli primarily through these specialized sensory cells located in its gastrodermis.

### Final Answer:
**(c) Sensory cells**