Figure 205 from Chapter 6 (Golgi Apparatus) of 'The Cell, 2nd Ed.' by Don W. Fawcett M.D. Sequence of the development of the acrosomal cap in spermatids from guinea pig testis, as observed in electron microscopic images. Initially, membrane-bound vesicles appear in the Golgi (A). These coalesce into larger proacrosomal granules (B), one of which attaches to the nuclear envelope (C) and the other vesicles appear to merge with the attached vesicle (D). Once attached, the acrosome further enlarges to its final volume, the Golgi apparatus leaves its surface and migrates to the caudal cytoplasm (E - G). A PDF copy of the accompanying chapter is available on the ASCB’s BioEDUCATE website.