Sperm cells are born in the testicles. From the testicles immature sperm are then moved into the epididymis where they mature and are sorted for viability. Upon ejaculation sperm are drawn out of the epididymis by the peristaltic action of the muscular vas deferens where they travel up over the bladder and down through the seminal vesicles where they are mixed with seminal fluids then out through the prostatic sperm ducts where other fluids including prostatic fluid are added to the ejaculate and finally the sperm containing semen is ejected from the body through the penis. Sperm makes up 5% or less of the total 2-5ml volume of ejaculate.