- The endostyle is found in protochordates (like Amphioxus). It secretes mucus to trap food particles.
- During evolution, the endostyle was modified into the thyroid gland in vertebrates.
- Atrium refers to a chamber in the heart.
- Pharynx is part of the digestive/respiratory system but not directly the thyroid precursor.
- Test refers to a protective covering (in tunicates), not endocrine-related.
Find the variance of the following frequency distribution:
| Class Interval | ||||
| 0--4 | 4--8 | 8--12 | 12--16 | |
| Frequency | 1 | 2 | 2 | 1 |