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The conch becomes one of the most definitive symbols in the novel. Found early on by Ralph and Piggy, the conch calls all of the boys together for their very first organized meeting, and many of the boys connect the creamy white shell to a trumpet, in their minds like the megaphone held by the man at the airport. In this way, the conch becomes a symbol of authority, which is later reinforced when Ralph chooses to make the conch a visual symbol in their chaotic meetings to help determine who has the right to speak.
The conch represents power-- the power to speak during meetings, but also the power to control the other boys by calling them to meeting. Because the conch is connected to Ralph's ideals of orderly meetings and tribal communitry, the conch also comes to represent in a larger sense, civilization itself. Only at the very end of the novel when the conch shatters during Piggy's death, does the reader gain a true sense that savagery has completely overrun the island.