through the 10th week of development. Despite the similarity in structure, function, and terminology, however, the mesonephric nephrons do not form any part of the mature kidney or nephrons. As the more caudal nephrons form, the more cranial nephrons are already degenerating. In females the mesonephros degenerates entirely, though vestigial structures such as Gartner's ducts, the epoophoron, and paroophoron are common. In males, a few of the more caudal tubules will survive and give rise to the efferent ductules of the testis, the epididymis, vas deferens, seminal vesicle, as well as vestigial structures such as the appendix testis, appendix epididymis, and paradidymis. Other animals The mesonephros persists and forms the anterior portion of the permanent kidneys in fish and amphibians, but in reptiles, birds, and mammals, it atrophies and for the most part disappears rapidly as the permanent kidney (metanephros) begins to develop during the sixth or seventh week. By the beginning of the fifth month of human development, only the ducts and a few of the tubules of the mesonephros remain. Additional images See also pronephros metanephros paramesonephric ducts, ducts beside (para-) the mesonephros References Embryology of urogenital system Kidney Scrotum