part of part of in taxon sperm acrosomal vesicle acrosomal granule A structure in the head of a spermatozoon that contains acid hydrolases, and is concerned with the breakdown of the outer membrane of the ovum during fertilization. It lies just beneath the plasma membrane and is derived from the lysosome. acrosome GO:0001669 Wikipedia:Acrosome secretory granule Eukaryota Fungi