Human vs. Cat Appendix: Single Vestigial vs. Multiple Immunologic

Human appendix: Single, worm-like diverticulum of cecum (avg 8–10 cm). Contains lymphoid tissue; proposed roles: microbiome reservoir, immune sampling. Appendectomy = no major deficit.

Cat appendix (cecal appendices): 2–4 (sometimes more) branched diverticula from cecum near ileocecal valve. Rich in lymphoid tissue; active in mucosal immunity – IgA production, lymphocyte maturation. Removal may impair immune defense.

Evolutionary Context

• Herbivores/omnivores often have prominent cecal appendices for fermentation/immunity.
• Humans: reduced, vestigial.