DEVELOPMENTAL VESTIGES. “Ontogenetic changes (i.e., developmental modifications occurring during an organism’s lifespan) can be more drastic than phylogenetic changes, perhaps due to the speed and scope with which development advances, and similarly reflect major biological processes. Nipples in male mammals provide a classic example.”
https://evolution-outreach.springeropen.com/articles/10.1186/s12052-014-0012-5