Facts in The Chambered Nautilus

The chambered nautilus is named for the expanding, spiraling series of “chambers” or “cells” that the nautilus constructs within its shell over the course of its lifespan. As the nautilus matures and grows in size, it periodically creates a new chamber before transporting its soft organs therein. The nautilus fills the previously inhabited, smaller chambers with controlled amounts of gas in order to adjust the ballast of its body as it ascends and descends through the oceanic depths.

In this case, the noun “main” refers to the sea. This definition of “main” is a truncation of “the main sea,” meaning “the powerful sea.” To call the sea “unshadowed” is a tonal flourish, intended to evoke the fanciful vision of the sea that prevails over the course of the poem. In reality, the chambered nautilus is a frequent denizen of the marine layer known as the dysphotic—or “twilight”—zone, ranging down to depths of 1,000 feet where sunlight barely penetrates.

Here Holmes introduces an important extended metaphor: that of the chambered nautilus as a ship at sea. With its buoyant, concave structure, the shell of the nautilus resembles the hull of a ship. However, to say it is a ship “of pearl” is not a metaphor. Like its fellow molluscs, the chambered nautilus fashions its shell out of nacre, a material better known as mother of pearl. With its pearlescent gleam and helical architecture, the nautilus shell has long stirred the curiosities of artists and collectors alike.