Three accessory glands of the male reproductive system are: Seminal vesicle, Prostate gland, Cowper's gland.
1) Seminal Vesicle: It is a pair gland present lateral to the urethra on both the side. 60% of the semen content is of seminal vesicle. It secretes fructose (gives energy to the sperm for swimming in the female genital tract), prothrombin and fibrinogens etc.
2) Prostate gland: It is a single gland present below the urinary bladder. It secretes 30% of the semen. It secretes acidic fluid. Prostate cancer is common cancer among the males.
3) Cowper's gland/Bulbourethral gland: It is a pair gland present laterally to the membranous urethra. It dose not contribute to the semen content but secretes fluid to neutralize the acidity of the urethra.
NOTE: SEMEN CONTAIN 60% SEMINAL FLUID, 30% PROSTATIC FLUID AND 10% SPERMS.