Early spermiogenesis in Rajonchocotyle emarginata. A, B, very early spermatid with round nucleus and mitochondria gathered above nucleus. The early zone of differentiation is lined with microtubules; constituents of the zone of differentiation visible as a densification of the cytoplasm. C, early zone of differentiation, with fully formed intercentriolar body and two centrioles. This section does not cut the nucleus. D, magnification of early zone of differentiation in A. Scales in all figures: 500 nm.