Select the correct statement.

Options

A. Pineal gland secretes melatonin
B. Vasopressin is secreted by kidneys
C. Endocrine system of invertebrates is very complex
D. `T_3` is secreted from follicular cells of parathyroid glands

Answer

To solve the question "Select the correct statement," we will analyze each of the given statements one by one.

### Step-by-Step Solution:

1. **Statement A: Pineal gland secretes melatonin.**
- The pineal gland is a small gland located at the base of the hypothalamus. It is known to secrete the hormone melatonin, which regulates sleep patterns and circadian rhythms.
- **Conclusion:** This statement is correct.

2. **Statement B: Vasopressin is secreted by kidneys.**
- Vasopressin, also known as antidiuretic hormone (ADH), is synthesized in the hypothalamus and released from the posterior pituitary gland. It is not secreted by the kidneys; rather, it acts on the kidneys to promote water reabsorption.
- **Conclusion:** This statement is incorrect.

3. **Statement C: Endocrine system of invertebrate is very complex.**
- The endocrine system in most invertebrates is either absent or very simple compared to vertebrates. Invertebrates typically have a less complex endocrine system, primarily for functions like molting and growth.
- **Conclusion:** This statement is incorrect.

4. **Statement D: T3 is secreted from follicular cells of parathyroid gland.**
- T3 (triiodothyronine) and T4 (thyroxine) are thyroid hormones secreted by the follicular cells of the thyroid gland, not the parathyroid gland. The parathyroid gland secretes parathyroid hormone (PTH), which regulates calcium levels.
- **Conclusion:** This statement is incorrect.

### Final Conclusion:
The only correct statement is **Statement A: Pineal gland secretes melatonin.**

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