Spermiogenesis in Rajonchocotyle emarginata, late zones of differentiation. A, B, longitudinal sections of late zones of differentiation embedded in the cytoplasm of the mass of spermatids. Arching membranes at the anterior (proximal) extremity. C, D, high magnification of arching membranes. E, high magnification of transverse section of late zone of differentiation. Two fully-incorporated axonemes, one section of mitochondrion, and almost complete row of peripheral longitudinal microtubules. Note dense material external to cell membrane, or “ornamentation”. F-I, various transverse sections of late zones of differentiation; the cytoplasm of the surrounding spermatid is often lined with membranes (several layers in I). Scale in D valid for C- I. Scales in all figures: 500 nm.