UROGENITAL VESTIGES. “”The best examples of non-functional embryonic ‘vestiges’ come from the developing urogenital system. Not only do excretory (urinary) and reproductive (genital) systems share many developing tubes but there is also shared ‘plumbing’ between developing males and females.”
https://evolution-outreach.springeropen.com/articles/10.1186/s12052-014-0012-5