Spermatozoon of Rajonchocotyle emarginata, anterior part. A-G and I-R, transverse sections, in antero-posterior sequence; H, longitudinal section. A, B, anteriormost part of spermatozoon: one axoneme, one centriolar derivative, peripheral row of microtubules and ornamentation on membrane. C-G, region of spermatozoon with membrane ornamentation. Microtubules generally as a single row of peripheral parallel units, two axonemes and section of mitochondrion. G shows together a typical section (right) and an intermediary section (left) with ornamentation only on ventral side of spermatozoon. H, longitudinal section in region with membrane ornamentation, showing axoneme with typical trepaxonematan 9 + ”1” structure, mitochondrion with very regular diameter, peripheral microtubules and external ornamentation on cell membrane (microtubules and ornamentation visible on both sides). I-K, various sections at the limit of region with ornamentation and region without ornamentation and additional microtubules. A section of mitochondrion is visible in all sections; a section of nucleus appears, with very small diameter. L-R, sections in the region posterior to membrane ornamentation, showing decreasing number of external microtubules and progressive appearance of section of nucleus. Scale in K, valid for all figures: 500 nm.