Genetic and physiologic control of fissioning and sexuality in planarians.

Several fissiparous strains of the planarian Dugesia gonocephala s.l. have been subjected for many months to continuous feeding on crushed tissues of sexually mature specimens of the planarians Polycelis nigra or (in a few cases) Dugesia lugubris. In a very high percentage of cases (especially after feeding on Polycelis nigra crushed tissues) the fissioning phenomena have been stopped and a sexual state has been induced. The sexualized specimens developed hyperplasic ovaries, testicular follicles and a more or less complete copulatory apparatus; some of them went so far as to lay sterile cocoons. As for the nature of sexualizing substances contained in crushed tissues of sexual planarians, further researches are required; we suggest they are neurosecretions stimulating sexuality and so inhibiting fissioning phenomena.