Sagittal histological sections of specimen after regenerating for 48 hours. Anterior is to the left in all panels. A-C. Various sections of a 1-hour-BrdU pulse specimen (cells in S-phase with orange-brownish nuclei). A. Whole specimen. Arrow points to male primordium. B,C. Sections through male primordium. Black arrowheads point to muscle fibres. D. Section through male primordium stained with Richardson’s stain. Note that the cells are arranged concentrically in a sphere but without any apparent organisation. Abbreviations: br, brain; cv, chordoid vacuole; ds, digestive syncytium; m, mouth; o, oocyte. Scale bars: A 50 μm; B, C, D 10 μm.