Which one of the following statements is totally wrong about the occurrence of notochord , while the other three are correct

Options

A. It is present only in larval tail in Ascidians
B. It is replaced by a vertebral column in adult frog
C. It is absent throughout life in humans from the very beginning
D. It is present throughout life in Amphioxus

Explanation

To determine which statement about the occurrence of notochord is totally wrong, we need to analyze each of the provided options based on our understanding of chordates and the characteristics of notochord.

### Step-by-Step Solution:

1. **Understanding Notochord**:
- The notochord is a flexible rod-like structure found in chordates. It is present during some stage of development, either in embryonic or adult forms.

2. **Analyzing Each Statement**:
- **Option A**: "It is present only in the larval tail in ascidians."
- This statement is **correct**. In ascidians (urochordates), the notochord is present only in the larval stage and is located in the tail.

- **Option B**: "It is replaced by the vertebral column in adult dogs."
- This statement is also **correct**. In vertebrates, including dogs, the notochord is present during embryonic development but is replaced by the vertebral column in adults.

- **Option C**: "It is absent throughout life in humans from the very beginning."
- This statement is **wrong**. Humans, being chordates, have a notochord during embryonic development, which is later replaced by the vertebral column. Thus, it is not absent from the very beginning.

- **Option D**: "It is present throughout life in amphioxus."
- This statement is **correct**. Amphioxus (cephalochordates) retains the notochord throughout its life.

3. **Conclusion**:
- The only statement that is totally wrong is **Option C**: "It is absent throughout life in humans from the very beginning." This statement contradicts the fact that humans have a notochord during embryonic development.

### Final Answer:
- The answer to the question is **Option C**.

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