The nervous system of vertebrates is derived from :

Options

A. Ectoderm
B. Endoderm
C. Mesoderm
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Germ Layers**: In vertebrates, the development of organs occurs from three primary germ layers: ectoderm, mesoderm, and endoderm. Each layer gives rise to different structures in the body.

2. **Identifying the Germ Layers**:
- **Ectoderm**: This is the outermost layer and is responsible for forming structures such as the skin, hair, nails, and the nervous system.
- **Mesoderm**: This middle layer forms structures such as muscles, bones, the heart, and the circulatory system.
- **Endoderm**: This innermost layer primarily forms the internal organs, including the liver and pancreas.

3. **Focusing on the Nervous System**: The question specifically asks about the origin of the nervous system in vertebrates. The nervous system includes the brain and spinal cord, which are crucial components of the central nervous system.

4. **Determining the Correct Germ Layer**: Since the nervous system develops from the ectoderm, we can conclude that the nervous system of vertebrates is derived from the ectoderm.

5. **Final Answer**: Therefore, the correct answer to the question is **ectoderm**.

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