Semen is made up of sperm (male cells for sexual reproduction) floating in a fluid called seminal plasma. Sperm, also called spermatozoa, are made by a man's testicles and mature (grow up) in the epididymis. The fluids in seminal plasma come from different glands in the man's body: the seminal vesicles, prostate and bulbourethral glands (also called the Cowper's glands). (Glands are special organs in the body that make chemicals.) The table below shows the substances that make up semen and the glands that produce them: