Name the hormone secreted by Pars intermedia in lower vertebrates.

Answer

### Step-by-Step Solution:

1. **Identify the Structure**: The question asks for the hormone secreted by the Pars intermedia in lower vertebrates. The Pars intermedia is a part of the pituitary gland.

2. **Understand the Pituitary Gland**: The pituitary gland is divided into two main parts: the adenohypophysis (anterior pituitary) and the neurohypophysis (posterior pituitary). The Pars intermedia is a part of the adenohypophysis.

3. **Hormones of the Pars Intermedia**: In lower vertebrates, the Pars intermedia primarily secretes one hormone.

4. **Name the Hormone**: The hormone secreted by the Pars intermedia in lower vertebrates is Melanocyte Stimulating Hormone (MSH).

5. **Function of MSH**: MSH acts on melanocytes, which are cells that produce melanin, the pigment responsible for coloration in skin and other tissues.

### Final Answer:
The hormone secreted by the Pars intermedia in lower vertebrates is Melanocyte Stimulating Hormone (MSH).

---