The appendix of the epididymis (or pedunculated hydatid) is a small stalked appendage (sometimes duplicated) on the head of the epididymis. It is usually regarded as a detached efferent duct.
This structure is derived from the Wolffian duct (Mesonephric Duct) as opposed to the appendix testis which is derived from the mullerian duct (Paramesonephric Duct) remnant.
See also 
This article incorporates text from a public domain edition of Gray's Anatomy.
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