ABSTRACT
Planarians* are free-living, nonparasitic, bilaterally symmetrical flat worms (dorsoventrally flattened). They range in size from about 3 to about 15 mm and are found throughout the world. There are several features that make planarians particularly noteworthy and valuable for pharmacologic study, including being the earliest extant example of cephalization (centralized nervous system’), capacity for rather complex behavior (‘learning and memory’) and ability to regenerate.
