Spermiogenesis in Rajonchocotyle emarginata, fully formed zones of differentiation. A, zone of differentiation at stage when free flagella are directed backwards along the zone of differentiation. B-E, longitudinal sections of fully formed zones of differentiation, showing typical morphology with elongate nucleus with lamellated chromatin, two centrioles, two striated roots, two free flagella and median cytoplasmic process. Mitochondria appear separate and roundish. F, high magnification of striated root, longitudinal section. G-H, transverse sections of fully formed zones of differentiation; row of peripheral microtubules in all sections. G, section in proximal part of zone of differentiation, showing nucleus and several mitochondria. H, I, sections at level of intercentriolar body and centrioles, with nucleus and/or mitochondria. Scales in all figures: 500 nm.