the plural of testis. or testicles Male reproductive organs (see reproductive system). Humans have two oval-shaped testes 1.5-2 in. (4-5 cm) long that produce sperm and androgens (mainly testosterone), contained in a sac (scrotum) behind the penis. Each testis is divided into 200-400 lobes containing three to 10 very thin coiled tubes (seminiferous tubules) each, which produce the sperm and contract to expel them through a complex network of canals to another structure in the scrotum, the epididymis, for temporary storage. The cells in the testes are undeveloped in early childhood; at puberty they are stimulated by hormones to develop into fertile sperm cells