Sperm cells. Illustration of sperm cells (or spermatozoa). These are the male sex cells, and are produced in the testes. They carry one half of the genetic material for a new human. The other half is in the female sex cell (ovum) with which one sperm merges during fertilisation. The genetic material of each sperm is carried in the rounded head, while its long tail is used to move itself. Some 300 million sperm are released by the male during ejaculation, as opposed to the one ovum the female releases in ovulation. A single sperm cell is less than 0.1 millimetres long.