Illustration of sperm cells (spermatozoa, white) moving into the ejaculatory ducts. Upon sexual stimulation, mature spermatozoa are transported through the vas deferens (sperm duct, arching tube) to the ejaculatory ducts. Here fluid from the seminal vesicles (pink and red structures, right) and the prostate (round pink structure) are added to the sperm to provide nutrients and added motility, forming semen. Spermatozoa are reproductive cells (gametes) which can fertilise the egg during sexual reproduction, and carry one set of chromosomes from one parent.