Open vascular system

Japanese: 開放血管系 - かいほうけっかんけい（英語表記）open vascular system

It is also called the open circulatory system or crevice circulatory system. It is a vascular system that lacks capillaries and in which all blood that passes through the arteries flows into the tissue spaces. Therefore, blood cannot be distinguished from lymph, and it is also called hemolymph. Blood in tissues returns to the heart through veins, gills, branchial vessels, pericardial space, etc., but in terrestrial insects, blood vessels are poorly developed compared to the development of the trachea, and blood flows directly into the heart. Among animals with a vascular system, it is often found in invertebrates such as arthropods, mollusks, and tunicates of protochordates.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

開放循環系，隙窩循環系ともいう。毛細血管を欠き，動脈を通過した血液がすべて組織間隙に流れ出すような血管系。したがって血液はリンパ液と区別できず，血リンパ液とも呼ばれる。組織中の血液は静脈，鰓，出鰓血管，囲心腔などを通過して心臓へ戻るが，陸生昆虫では気管の発達と逆に血管の発達が悪く，直接心臓へ入る。血管系をもつ動物のうち，節足動物，軟体動物，原索動物の被嚢類など，無脊椎動物に多くみられる。

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