During regeneration in planarians, anterior (head and prepharyngeal) and posterior (postpharyngeal and tail) fragments rebuild one of the most peculiar structures of planarians: the pharynx and the pharynx cavity. Previous studies (see Brnsted, 1969, for a general review, and Asai, 1990, 1991, for anterior regeneration) have shown that within postpharyngeal pieces both structures appear in the old stump from clusters of undifferentiated cells. However, the lineage and differentiation of their elements (inner and outer epithelial cells, muscle layers, gland cells, nerve rings) and the overall pattern of growth and differentiation is not clear.