Mesonephros

Part of speech: noun

Definitions

1. An organ embryonically developed in vertebrates that contributes to kidney formation during a specific developmental stage
2. A segment of the embryonic excretory system in lower vertebrates, which plays a role in the formation of the permanent kidneys
3. A structure found in the early development of fish and amphibians that serves as a functional excretory organ before the constitutive kidneys develop

Etymology: The name is a plain piece of Greek-based scientific compounding: "meso-" from Greek "mesos", meaning "middle", joined to "nephros", meaning "kidney". The result describes an organ that sits in the middle of the developmental series of kidneys. In vertebrate embryos, three successive kidney systems appear in turn, and the mesonephros is the middle one, following the pronephros and preceding the metanephros, which becomes the adult kidney in mammals. The Greek roots are ancient, with "mesos" traceable back through Proto-Hellenic to a Proto-Indo-European base meaning "middle", and "nephros" carrying the sense of kidney. The compound itself, however, is a modern technical coinage built from these classical elements, not a term the ancient Greeks would have recognised. Anatomists assembled it in the scientific vocabulary of the nineteenth and twentieth centuries, using the same method that produced many other embryological names.