Dedifferentiation and redifferentiation of the penis of the freshwater planarian Bdellocephala brunnea

Following decapitation of Bdellocephala brunnea and subsequent repeated removal of regenerating head-blastemas, the copulatory apparatus degenerated within 40-60 days. The copulatory apparatus disintegrated into cell clusters that further divided into separate neoblast-like cells that, in turn, eventually transformed into ordinary parenchymal cells by 60 days after decapitation. When the head of worms with a degenerate copulatory apparatus was allowed to regenerate by discontinuing excision of the head blastema, a new copulatory apparatus differentiated, ostensibly from the dedifferentiated cells. The neoblast-like cells appear to participate in the redifferentiation of the penis and of other parts of the copulatory apparatus.