The second of the three excretory organs that develop in a vertebrate embryo, becoming the functioning kidney in fish and amphibians but replaced by the metanephros in higher vertebrates.

• 中肾在脊椎动物胚胎内发育而成的三对排泄器官中的第二对，作为功能肾存在于鱼类和两栖类体内，但在更高级的脊椎动物中则发育成后肾