The epididymis (/ɛpɨˈdɪdɨmɪs/; plural: epididymides /ɛpɨdɨˈdɪmədiːz/ or /ɛpɨˈdɪdəmɪdiːz/) is a tube that connects a testicle to a vas deferens in the male reproductive system. It is present in all male reptiles, birds, and mammals. It is a single, narrow, tightly-coiled tube (in adult humans, six to seven meters in length) connecting the efferent ducts from the rear of each testicle to its vas deferens.