Cestodes or tapeworms are more or less elongated, flattened, and segmented bodies that attach themselves to the mucous membrane of the intestine by means of suckers or hooklets.

They have no alimentary canal. Are hermaphroditic. One cycle of their life-history is in man, the other in some one of the lower animals. The fully developed worm is called a strobile. It consists of a head, a very narrow neck, and a number of segments called proglottides. These segments complete or the eggs from them escape in the feces. They are then taken up in the food, the covering of the egg digested, and the embryos penetrate the tissues, ultimately lodging in the voluntary muscles and elsewhere. The embryo worm when lodged in the tissues is called a scolex, consisting only of a head and vesicular body without a trace of organs, and is surrounded by a bladder-like body known as a cysticercus. When the animal food is eaten, the embryos are set free, and attach themselves to the intestine.