Illustration showing the internal anatomy of the human testis (testicle), part of the male reproductive system. The testes are where the male sex cells (spermatozoa) are produced. This process, called spermatogenesis, occurs in the seminiferous tubules, seen coiled in the main body (round, purple) of the testicle. The coiled structure leading out of the testicle is the epididymis. This carries the sperm to the spermatic duct (vas deferens, bottom) that ascends into the abdomen.