ink sac

ink +‎ sac

ink sac (plural ink sacs)

1. (zoology) A muscular bag found in certain cephalopods used to generate ink.
   • 2017 August 9, Mark Carnall, The Guardian‎:

     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.

• incask