The mesonephros is a temporary kidney structure that develops in the early stages of vertebrate embryos, including humans. It forms after the pronephros and before the metanephros, serving as a functional organ for filtering waste and producing urine during early development. In humans, the mesonephros appears around the fourth week of gestation and is largely replaced by the metanephros by the end of the first trimester. While it plays a crucial role in embryonic development, the mesonephros does not persist into adulthood and is eventually absorbed by the body.