| the respiratory organ of a spider, scorpion, or other arachnid, composed of thin, membranous structures arranged like the leaves of a book. |
| book lung n. A saccular respiratory organ found in some arachnids, such as scorpions and spiders, consisting of several parallel membranous folds arranged like the pages in a book. |
book lung  (b k) Pronunciation Key
The breathing organ of scorpions, spiders, and some other arachnids. It consists of membranes arranged in several parallel folds like the pages of a book. |
book lung
form of respiratory organ found in certain air-breathing arachnid arthropods (scorpions and some spiders). Each book lung consists of a series of thin plates that are highly vascular (i.e., richly supplied with blood) and are arranged in relation to each other like the pages of a book. These plates extend into an internal pouch formed by the external skeleton that opens to the exterior by a small slit. This provides an extensive surface for the exchange of oxygen and carbon dioxide with the surrounding air. There are four pairs in scorpions and up to two in spiders.
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