Illustration of ejaculatory fluid from the seminal vesicles (top right) being added to sperm cells (spermatozoa, white) in the ejaculatory ducts. Spermatozoa enter the ejaculatory ducts from the vas deferens (sperm duct, top centre-left). The fluid from the seminal vesicles is added to the sperm to provide nutrients and added motility. Spermatozoa are reproductive cells (gametes) which can fertilise the egg during sexual reproduction, and carry one set of chromosomes from one parent.