I find the topic of this thread intensely interesting, so I've been doing a bit of digging of my own. To my surprise, I discovered that some animal worms live in a pouch which forms just after the junction between the small and large intestine. This pouch is called the Caecum, and in the human body terminates in the appendix.
To my amazement, the appendix may not be a vestigial organ at all but may play a vital role, especially early in life, in the development of the immune system! If human intestinal parasites hook into the appendix, they can muck about to their heart's content... just like R2-D2 plugging into the Deaths Star's mainframe, (do I win the prize for the worst analogy on this site?).
I'm afraid I've gone and lost the links and references I had, but if I find them again I'll edit this post.
"Although quite presumptive, it might actually be possible especially since some pathogens, such as the Epstein-Barr virus which is known to cause lymphoma, can be contracted through consumption of undercooked food. Hence, although it is not proven, the appendix might actually have the capacity to prevent a variety of deadly diseases by giving the body the protection it needs through the production of numerous antibodies that combat pathogens that enter the body via food consumption."
"...theory suggests that the human appendix—as well as the tonsils, the spleen, lymph nodes, and bone marrow—manufacture the antibody-producing white blood cells called B-lymphocytes. " "The Human Body." Science Fact Finder. Ed. Phillis Engelbert. UXL-Gale, 1998. eNotes.com. 2006. 7 Feb, 2007 <http://science.enotes.com/science-fact-finder/