Male reproductive organs (seereproductive 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.