noun. A caplike structure at the anterior end of a spermatozoon that produces enzymes aiding in egg penetration.

noun. In cytology, the body which forms the extreme anterior portion of the spermatozoön. Von Lenhossek, 1897.

noun. A structure forming the end of the head of a spermatozoon.

noun. a process at the anterior end of a sperm cell that produces enzymes to facilitate penetration of the egg

"In order to accomplish this the head of each sperm called the acrosome contains a packet of shell-dissolving enzymes—released when contact with the egg is made."

appendage  outgrowth  process