Sperm cells. Coloured scanning electron micrograph (SEM) of human sperm cells or spermatozoa. These tiny male sex cells are produced in the testes, and are responsible for fertilisation of the female egg (ovum). Each sperm has a rounded head which contains the male hereditary material (DNA) Some 300 million sperm are released by the male during ejaculation, while the female usually produces one large egg at a time. Only one sperm cell can fertilise the egg. Magnification: x4000 when printed at 10cm. wide.