Specimens regenerating for three days. Anterior facing upwards in A,B,C,D and to the left in E and F. White arrows point to bursal nozzle, black arrowheads to male primordium. A. Slightly squeezed live specimen. B. Posterior end of squeezed live specimen. C. Horizontal CLSM projection of whole specimen. Note that the inner muscles bend away from the male primordium. D. Horizontal CLSM projection of primordia of copulatory organs. E. Sagittal histological section through primordia of copulatory organs. White arrow points to densely stained part of developing bursal nozzle. F. Ultrathin section of male primordium. White arrowheads point to prospective longitudinal muscle fibres of the penis. Abbreviations: bwm, body-wall musculature; cv, chordoid vacuole; ds, digestive syncytium; fp, female primordium; mp, male primordium; st, statocyst. Scale bars: A, C 100 μm; B 25 μm; D, E 20 μm; F 10μm.