ink sac

noun

a large gland in most cephalopods, as the cuttlefish, octopus, and squid, that is near the rectum and ejects ink at predators.
a flexible structure containing ink.

Unlike most octopuses, dumbos don’t have ink sacs, perhaps because they have very few predators in the deep sea.

The ink taken from the ink-sac of Sepia is an article of commerce.

They are without an ink-sac, and have the foot divided into lobes bearing sheathed tentacles.

The ink-sac, absent in Nautilus, is a rectal caecum developed from its dorsal wall.

In certain cases remains of the arms provided with hooks, and of the ink-sac, have been recognized.

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