Cross-sections of spermatozoa of R. speculum. A Showing acrosome (a) B, C transition region between the acrosome (a) and nucleus (N), showing acrosome (a) on both sides of the nucleus (N), until it locates on just the one side of nucleus (N) D oval nucleus (N) E–I nucleus-flagellum transition region, showing the nucleus (N), mitochondrial derivatives (md), accessory bodies (ab), axoneme (ax), the asterisk indicates the centriolar adjunct (ca) and the arrow indicates the centriole (c). Scale bars: 0.5 µm (A, I); 0.1 µm (B–H).