In 1732 Laurentius Heister1 first described the valvular arrangement of the mucous membrane of the cystic duct that bears his name. He attributed to these leaflets projecting into the cystic duct a functional rôle of the gallbladder, namely, the storage of bile. Recent studies are at variance with this hypothesis; for this reason I undertook an anatomic and experimental study of the problem in 1923. The mucous folds in the cystic duct apparently reach their highest development in man. They are present in the dog, rabbit and a few other animals, but are less developed and fewer in number. A study of the comparative anatomy, therefore, suggests the very minor part played by these leaflets in the functional activity of the gallbladder. Indeed, in many species there are no leaflets and this must be considered in attempts to ascribe a functional rôle to the valves. Certainly their absence lessens