Consideration of the organization, ontogeny, and orientation of tapeworms, and comparison with the structure and development of other invertebrates, support the opinion that the cestode is an individual rather than a colony and that the transformation of the oncosphere to a procercoid or cysticercoid is a true metamorphosis in which there is a reversal of the antero-posterior axis. T EAPEWORMS have been known for thousands of years, and the ancients believed that both the segmented and bladder-worm stages arose spontaneously in the bodies of other animals. In the middle of the last century, Kiichen