Final answer:
The caecum is the first part of the large intestine, and the appendix is attached to the caecum. The appendix contains lymphoid tissue which suggests an immune function, though it has been viewed as a vestigial organ.
Step-by-step explanation:
The caecum and appendix are parts of the digestive system, specifically within the large intestine. The caecum is a pouch located at the start of the large intestine, right after the ileocecal valve, where the small intestine ends. Attached to the caecum is the appendix, a narrow, tube-like structure. While the appendix has been considered a vestigial organ, current research suggests it may play a role in maintaining a healthy balance of bacteria in the gut or may have an immunological function, especially as it contains lymphoid tissue. Appendicitis is a condition where the appendix becomes inflamed and infected, often leading to a surgical procedure called an appendectomy to remove the appendix.