Tapeworms: Cestoda

Scientists know little about the behavior of tapeworms in the intestines of their hosts. It seems that most tapeworms attach themselves at a certain site of the intestinal wall and stay there for their entire lives.

Tapeworms follow this general scheme as their life cycle. The eggs, each holding an embryo (EHM-bri-yo), pass into the environment with the final host's feces and are eaten by the intermediate host. In the intestine of the intermediate host, the embryos hatch and, using their hooks, bore through the intestinal wall and into the body cavity or an internal organ. In the new location the embryos transform into larvae. In most species the larvae have a fully developed scolex identical to that of adult tapeworms. The larvae enter the final host when it eats the intermediate host. In the final host the scolices (SKOH-luh-seez, the plural of scolex) of the larvae attach to the intestinal wall. The necks of the larvae start production of proglottids, and the strobila forms. With further development of proglottids, the worm starts producing eggs, which are released with feces into the environment. Some tapeworms have more than one intermediate host.

Most tapeworms make both eggs and sperm. Each proglottid contains one set of male reproductive organs and one set of female reproductive organs. In most species the male organs mature first, and proglottids first act as male organs. In species in which the female organs develop first, sperm develop in the male organs when the eggs develop in the female organs. Sperm from one tapeworm enter the female reproductive organs of another tapeworm during mating and are stored for a while before joining with eggs for the start of development of embryos.