Fig. 1

Ultrastructure of the spermatozoon of Lepidodasys sp. a Longitudinal section of the apical region (aa) of the acrosome. b Longitudinal section of the acrosome including the apical region and basal regions (ba). c Cross-section of the apical acrosomal region. d Longitudinal section of the basal region of the acrosome containing material organized into irregular vesicles (arrow). e Longitudinal section of the basal acrosomal region and of the nuclear base. f Cross-section of the basal region of the acrosome. g Longitudinal section of the nucleus–mitochondrion complex: the spiralized nucleus (n) surrounds the mitochondrion (arrows). h Longitudinal section of the ‘connecting piece’ (arrow head) lying in a cavity at the nuclear base. The mitochondrion is also visible (arrows). i Oblique and cross-section of the nucleus surrounding the mitochondrion (m). j Small electron-transparent spaces (s) with various size are regularly arranged into the condensed chromatin along the whole nuclear length. k Cross-section of the flagellum. l Schematic reconstruction of the mature spermatozoon