Fig. 1.

A demonstration that the normal ‘rouleaux’ formation of the spermatozoa is preserved throughout the slam-freezing and freeze-substitution procedure. This rouleau comprises four sperm sectioned at the level of the acrosome. The heads are linked together by the well known membrane appositions (arrowed) – see Friend & Fawcett (1974). However, granular material, containing vesicles, is also present between the sperm heads (double arrows); this material is scarcely preserved at all in conventionally fixed cells (loc. cit.). Scale bar=2µm.