Planarians have been used as a model to study development and regeneration for
more than 200 years. Research on these animals has traditionally focused on surgical and pharmacological
manipulations. Recently, the dissection of planarians has become more molecular in nature. The isolation
of thousands of ESTs and the introduction of in situ hybridizations, immunocytology, and
RNA-mediated gene interference (RNAi) has opened the door to gene discovery and to the study of gene function
in planarians during development and regeneration. These advances promise to shed mechanistic insight into
basic biological attributes such as regeneration and stem cell regulation.