The mesonephros (Latin for "middle kidney") is one of three excretory organs that develop in vertebrates (after pronephros and before metanephros).
The mesonephros serves as the main excretory organ of aquatic vertebrates and as a temporary kidney in higher vertebrates.
The mesonephros is included in the Wolffian body after Caspar Friedrich Wolff who described it in 1759. The Wolffian body is composed of the mesonephros and the paramesonephrotic blastema.
The mesonephros is composed of the mesonephric duct (also called the Wolffian duct), the mesonephric tubules, and the associated capillary tufts.
A single mesonephric tubule and its associated capillary tuft is called a mesonephric excretory unit. These units are similar in structure and function to nephrons of the adult kidney. The mesonephros is derived from intermediate mesoderm in the vertebrate embryo.
In human males, the mesonephros gives rise to the efferent ductules of the testis, the epididymis, vas deferens, seminal vesicle, and vestigial structures such as the appendix testis (hydatid of Morgagni), appendix epididymis, and paradidymis.
In human females, the mesonephros largely regresses though vestigial mesonephrotic structures such as Gartner cysts, the epoophoron, and paroophoron are common.
In animals
The mesonephros persists and form the permanent kidneys in fishes and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) develops begins during the sixth or seventh week, so that by the beginning of the fifth month only the ducts and a few of the tubules of the mesonephros remain.
See also
pronephros
metanephros
paramesonephric ducts