Spermatozoon of Rajonchocotyle emarginata, posterior part. A-I, transverse sections, in antero- posterior sequence. A-C, section with two axonemes, mitochondrion, nucleus with various degrees of dilatation, and peripheral microtubules. The nuclear envelope often has additional membranes. D-F, sections with a single axoneme, mitochondrion, nucleus, and peripheral microtubules. G, single axoneme, section of nucleus with dense chromatin and small diameter, mitochondrion with very small diameter, and peripheral microtubules. H, I, extremity with section of nucleus and no mitochondrion. A few microtubules present. Scale in C, valid for all figures: 500 nm.