nephridium

Japanese: nephridium

…The kidney is an excretory organ common to all vertebrates, and its main function is to release waste products, mainly nitrogenous metabolic products, from the body. It also has other functions, such as the excretion of water to regulate the osmotic pressure of body fluids, the excretion of excess components in body fluids, the excretion of alkaline or acidic substances to maintain a constant pH level in body fluids, and the excretion of harmful or unnecessary substances, and these functions are interrelated. The kidney is thought to have originated from the nephridium, and is divided into the pronephros, mesonephros, and metanephros based on the developmental order and position (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. …

From [Discharge]

…This process is repeated periodically to maintain a constant osmotic pressure within the cells. A typical protonephridium is found in the flatworm planarian, where it branches out in a complex network from the main ducts on both sides of the body, with flame cells at the ends (Figure 1). There are a pair of outlets that open on both sides of the center of the body. …

*Some of the terminology that mentions "nephridium" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

Japanese:

…腎臓は脊椎動物に共通する排出器官で，老廃物，おもに窒素代謝産物の体外への放出がその主要な働きであるが，体液の浸透圧調節のための水分の排出，体液中の余剰成分の排出，体液を一定のpHに保つためアルカリ性または酸性物質の排出，有害あるいは不要物質の排出などの機能ももっており，これらの諸作用は互いに関連し合っている。　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。…