The hormone of pars intermedia is responsible for :

Options

A. Darkening of skin in lower vertebrates
B. Regulates the growth of the mammary glands and formation of milk in them
C. It stimulates milk ejection from the mammary gland
D. Stimulates the synthesis and secretion of steroid hormones called glucocorticoids

Answer

**Step-by-Step Solution:**

1. **Identify the Hormone of Pars Intermedia**: The pars intermedia is a part of the pituitary gland that secretes hormones. The primary hormone produced by the pars intermedia is the Melanocyte Stimulating Hormone (MSH).

2. **Understand the Function of MSH**: The main role of MSH is to regulate the production of melanin by melanocytes in the skin. This process is responsible for the darkening of the skin, particularly in lower vertebrates.

3. **Evaluate the Options Given**:
- **Option A**: Darkening of skin in lower vertebrates - This is correct as it relates to the function of MSH.
- **Option B**: Regulates the growth of mammary glands and formation of milk - This is incorrect as this function is associated with the hormone prolactin, which is secreted by the anterior pituitary.
- **Option C**: Stimulates milk ejection from the mammary glands - This is incorrect as this function is performed by oxytocin, which is secreted by the posterior pituitary.
- **Option D**: Stimulates the synthesis and secretion of steroid hormones called glucocorticoids - This is incorrect as glucocorticoids are produced by the adrenal cortex, not the pars intermedia.

4. **Conclusion**: Based on the evaluation of the options, the correct answer is **Option A**: The hormone of pars intermedia is responsible for the darkening of skin in lower vertebrates.

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