Fluid produced by the male on ejaculation from the penis at sexual orgasm. Each ejaculate contains up to 500 million spermatozoa (male germ cells) suspended in a fluid that is secreted by the PROSTATE GLAND, seminal vesicles (see TESTICLE), and Cowper's glands – a pair of small glands (also called the bulbo-urethral glands) that open into the URETHRA at the base of the penis. Semen, or seminal fluid, contains a form of sugar (fructose) essential for the motility of sperm. The hormone TESTOSTERONE is a key element in the production of sperm and of seminal fluid.