Which of the following is correct about nematocyst ?

Options

A. it can be re-used
B. its ejection is conditioned reflex
C. it is ejected on contact and pierce they prey
D. due to which other Hydra doesn't come in contact with it

Explanation

To answer the question regarding the correct statement about nematocysts, we can break down the information as follows:

### Step-by-Step Solution:

1. **Understanding Nematocysts**:
- Nematocysts are specialized cells found in cnidarians, such as hydra. They are responsible for stinging and capturing prey.

2. **Activation of Nematocysts**:
- Nematocysts are activated by various stimuli, including touch, chemicals in the water, vibrations, or nerve impulses from the organism itself.

3. **Mechanism of Ejection**:
- Upon activation, nematocysts are discharged from the specialized cells called cnidocytes. This discharge occurs when the nematocyst comes into contact with a target (prey or predator).

4. **Effect on Prey**:
- The ejection of nematocysts pierces the prey and can cause paralysis or death, allowing the hydra to capture its food effectively.

5. **Reusability of Nematocysts**:
- Once a nematocyst is discharged, it cannot be reused. Instead, new nematocysts are formed through cell division in the interstitial cells of the epidermis.

6. **Conditioned Reflex**:
- The ejection of nematocysts is not a conditioned reflex. Conditioned reflexes are learned responses to stimuli, while the activation of nematocysts is an innate response.

### Conclusion:
The correct statement about nematocysts is that they are ejected on contact and pierce the prey, causing paralysis or death.