Formation of malformed pharynx and neoplasia in the planarian Bdellocephala brunnea following treatment with a carcinogen

The effect of benzo(a)pyrene on regeneration of the pharynx in Bdellocephala brunnea Ijima et Kaburaki was studied by inserting a 5-µg crystal of this carcinogen into the pharyngeal cavity of worms from which the pharynx had been extirpated 2 d previously. Multiple pharynges formed in the regenerates, and neoplasia was induced in a few cases. The malformed pharynges appeared as protrusions overlapping the anterior part of the main pharynx. Electron microscopy of the pharynx in normal, intact worms shows eight layers comprising inner and outer ciliated epithelia, muscle, and glands.