You and your cat might share a love of tuna and milk. You and your cat might even both enjoy playing with lasers and chasing mice. One thing you don't have in common is a certain vestigial organ -- namely, the appendix. You have one and your cat doesn't.
What's An Appendix, Anyway?
Unless you've had it removed, odds are you have an appendix. It's a thin, tubular structure on your cecum, which is a pouch near the point your intestines join together. Despite its location, biologists and doctors don't believe the appendix helps with digestion -- at least not in humans -- and it remains widely regarded as a vestigial organ (an organ that has lost its one-time function through evolution). A growing body of scientific evidence, however, suggests that the appendix plays a role in the human immune system, according to Scientific American and Web MD.
Who Has One?
Humans have appendixes, but they're irregular in light of the rest of the animal kingdom. Some plant-eating vertebrates have larger appendixes that appear to help digest large amounts of vegetation. Rabbits and some rodents have them, but your cat doesn't have one. Most animals don't have appendixes or, if they do, only rudimentary ones. Cats are in a bit of a gray area. They don't really have appendixes, but they do have rudimentary organs, appendix-like structures, although their function isn't well understood.
While your cat doesn't have an appendix, he does have a structure that appears to function similarly to one. In 1974 a group of researchers published a paper describing the "rudimentary appendix of the cat," which has been cited in multiple scientific works in the decades since then. Still, understanding of the organ has changed since then, and there doesn't appear to be much contemporary research in this arena. Just because this organ is in the same place as appendixes in other animals doesn't mean it serves the same function in cats. Your cat's rudimentary appendix is neither large nor complex enough for it to swell enough to necessitate its removal. That's right: Your cat will never have appendicitis.
Considering the fact that cats are obligate carnivores -- they have to eat meat to survive and can't live on vegetarian diets -- it shouldn't be particularly surprising that they don't really have appendixes. Your cat's penchant for chewing on your favorite house plant, however, might persuade you otherwise. Cats eat grass and other flora to get folic acid. They don't need to eat the greenery for this, technically speaking, but they end up swallowing some anyway. It helps as a laxative, too, if they can keep it down long enough to digest it. It's unclear whether human-like appendixes would help them in this regard, but it's clear cats have thrived for thousands of years without them.