Ink sac


  • Webster's Revised Unabridged Dictionary
    • Ink sac (Zoöl) an organ, found in most cephalopods, containing an inky fluid which can be ejected from a duct opening at the base of the siphon. The fluid serves to cloud the water, and enable these animals to escape from their enemies. See Illust. of Dibranchiata.
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In literature:

Identify the long plume-like gills, the ink sac, and the inner opening of the exhalent siphon.
"A Guide for the Study of Animals" by Worrallo Whitney
Belemnites have sometimes been sketched with fossil sepia, or india ink, from their own ink sacs.
"The Elements of Geology" by William Harmon Norton