Adult tapeworms are all parasites of vertebrates, living almost always in the intestines. They have become so well adapted in their parasitic life that they no longer have a digestive system, not even a mouth. They absorb digested food from their host directly through their body wall. The head has suckers and hooks, which enable the tapeworm to hang onto the host's intestine walls. The extremely long ribbon-like body is composed of many segments.
Each segment in a tapeworm is really a reproductive apparatus, complete with male and female sex organs. When a segment matures, it contains thousands of fertilized eggs. Mature segments, laden with fertilized eggs, are continuously dropped off the tail end of the worm and leave the host animal with the feces as new ones develop near the neck of the worm. Thus, the tapeworm is clearly an impressive reproductive machine that turns out egg packages on an assembly line basis, one after the other. In man, tapeworms have been know to reach a length of 70 feet and may contain hundreds of segments. The most commonly encountered tapeworm is the beef tapeworm, which can be avoided by never eating beef rare, but well done.