Pronephros

… The kidney is thought to have originated from the nephridium, and is divided into the pronephros, mesonephros, and metanephros based on the order and location of development (Figure 1). The pronephros, which appears first, is funnel-shaped and opens into the body cavity, and is considered to be the primitive form of the kidney. In the cyclostome hagfish, the pronephros functions together with the mesonephros that develops later, but in cartilaginous fish and reptiles and above, the pronephros is vestigial and degenerates from the beginning and has no function. …

*Some of the terminology explanations that mention "pronephros" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…　腎臓は腎管nephridiumに由来したものと考えられ，発生上の順序や位置から前腎，中腎および後腎に分けられる(図1)。最初に現れる前腎pronephrosは漏斗状となって体腔に開き，腎臓の原始型とみられる。円口類のメクラウナギでは前腎がその後に発達する中腎とともに機能を営むが，軟骨魚類と爬虫類以上では前腎が初めから退化痕跡的で作用をもたない。…

※「pronephros」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報