Which one of the following statements is incorrect about the occurrence of notochord ?

Options

A. It is present only in larval tail in ascidian
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 incorrect, we will analyze each option provided in the question:

1. **Option 1**: "It is present only in the larval tail in the ascidian."
- **Analysis**: Ascidian, which belongs to the Urochordata, has a notochord that is indeed present only in the larval stage, specifically in the tail. In adult ascidians, the notochord is absent. This statement is correct.

2. **Option 2**: "It is replaced by a vertebral column in the adult frog."
- **Analysis**: Frogs are classified under Amphibia, which is part of the Vertebrata. In adult frogs, the notochord is replaced by a bony vertebral column. This statement is also correct.

3. **Option 3**: "It is absent throughout the life in humans from the very beginning."
- **Analysis**: Humans are mammals and also part of the Vertebrata. While the notochord is present during early embryonic development, it is replaced by the vertebral column during development. Therefore, this statement is incorrect, as the notochord does exist in the embryonic stage before being replaced.

4. **Option 4**: "It is present throughout the life in the amphioxus."
- **Analysis**: Amphioxus, which belongs to the Cephalochordata, retains its notochord throughout its life. This statement is correct.

**Conclusion**: The incorrect statement about the occurrence of notochord is **Option 3**: "It is absent throughout the life in humans from the very beginning."