Male reproductive system
Testicles are small ball-like organs. An adult testicle size is about 4 to 5 cm long. The testicles produce sperm cells from teenage years to old age. The sperm cells are produced in the seminiferous tubules, which are the main part of the testicles. After the sperms are produced, they are stored temporarily in the epididymis. The epididymis is covering the top of the testicle.