1911 Encyclopædia Britannica/Bladder - Wikisource, the free online library
BLADDER (from A.S. blaēddre, connected with blāwan, to blow, cf. Ger. blase), the membranous sac in animals which receives the urine secreted from the kidneys. The word is also used for any similar sac, such as the gall-bladder, the swim-bladder in fishes, or the small vesicle in various seaweeds.