ink sac

— The ink sac feeds into the rectum, controlled by a sphincter and in some inking events mucus from another organ, the funnel organ is ejected with water and ink through the anus and the siphon to create a cloud of ink. […] Fossils are particularly well described from the Carboniferous, Triassic, Jurassic and Cretaceous periods and have been found in the USA, England, Russia, Lebanon and Germany. Sites such as Lyme Regis in Dorset have particularly yielded number of Jurassic “squid” ink sacs and nodules (Doguzhaeva et al. 2004).