Also found in: Thesaurus, Medical, Encyclopedia, Wikipedia.
One of the paired saccular respiratory organs found in some arachnids, such as scorpions and spiders, consisting of several parallel membranous folds arranged like the pages in a book.
the respiratory organ of many arachnids, composed of thin, paperlike layers of tissue.
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.