Venom sac

You may be looking for Venom gland.

Bees usually lost their venom sacs when they lost their stings. (PROSE: Eater of Wasps ^[+]Loading...["Eater of Wasps (novel)"])

Kagawan lizards had venom sacs from which the Kagawa Virus was synthesised. (PROSE: Virus ^[+]Loading...["Virus (short story)"])

Zygons carried venom sacs in their tongues. (TV: The Day of the Doctor ^[+]Loading...["The Day of the Doctor (TV story)"])