In the poem’s final lines, the nautilus reaches the state of freedom it seeks by leaving behind its “outgrown shell” entirely. Building on the themes of the final stanza, the nautilus is only able to achieve its spiritual aim by shedding its body. The religious idea that the physical, sensuous world blocks us from uniting with a veiled transcendent reality has roots in the Judeo-Christian and Gnostic traditions. In the Christian tradition, access to transcendence—figured as heaven—generally only occurs after the death of the body. In the Gnostic tradition, access to transcendence is an epistemological quest that results in gnosis, the Greek word for “knowledge.” The American transcendentalist movement, spearheaded by Ralph Waldo Emerson, repurposed some of the principles of Gnosticism, and Oliver Wendell Holmes was profoundly influenced by Emerson’s writings.

In a continuation of the metaphor of the shell’s chambers as mansions that mark one’s progress, Holmes swaps out “mansions” for “temples,” explicitly signalling the spiritual nature of the progress. These ever larger and “nobler” temples, however, “shut thee from heaven,” suggesting that the temples are ultimately limiting constructs, preventing the nautilus from reaching the numinous reality it seeks.

The final stanza represents the message of the nautilus, as recorded—perhaps imaginatively—by the speaker. Addressing “my soul,” the nautilus says, “build thee more stately mansions.” On one level, this is an extension of the shell-as-house metaphor, referring to the series of “mansions” the nautilus builds for itself. On an allusive level, this draws on the Bible, specifically John 14:2, in which Jesus says, “In my Father's house are many mansions.” At this level, the mansions are a spiritual, metaphysical construction, perhaps representing the layers of experience and development that accrue over the course of one’s life.

The phrase “deep caves of thought” applies two new metaphors to the nautilus shell. The first is that of “deep caves,” an apt image for the receding chambers within the spiraling shell. The other is that of a brain or, more conceptually, a mind—in either case, the source of “thought.” The metaphors are nested, for “deep caves” also serves as a vehicle for the tenor of “thought”—both of which, in turn, serve as a vehicle for the nautilus itself as it dispenses its treasured wisdom to the speaker.

Triton was a Greek deity, a minor sea god and a son of Poseidon. According to most descriptions, he was half-man and half-fish. In his service as an emissary for Poseidon, he used a horn fashioned out of a conch, or sea snail, shell. One of the largest sea snails, the Charonia tritonis, is named after Triton. This phrase, down to the accent on “wreathèd,” is taken from the final line of William Wordsworth’s (1770–1850) sonnet “The World Is Too Much with Us”: “Or hear old Triton blow his wreathèd horn.”

In the penultimate stanza, the speaker turns his attention to a “message” delivered by the nautilus, supposedly emanating from within the shell. It is a “heavenly message,” despite the origins of the nautilus being the “wandering sea,” rather than a classically empyrean heaven. This turn towards the heavenly indicates the poem’s shift toward spiritual themes.

The phrase “stole with soft step” uses rich consonance—a litany of s and t sounds—to convey the susurrous action of the nautilus as it moves its soft body from one chamber of its shell to the next.

This stanza describes the process by which the nautilus matures, creates new shell chambers, and moves its organs. Holmes employs the intuitive metaphor of moving houses, as if the nautilus were changing dwellings on a yearly basis—an accurate characterization.

Holmes employs an unusual structure by writing “The Chambered Nautilus” in five septets, or seven-line stanzas. The rhyme scheme represent a slight variation on rhyme royal, a septet-based rhyme scheme introduced by Geoffrey Chaucer in the 14th century. Whereas Chaucer’s septets follow an ABABBCC scheme, Holmes’s go AABBBCC. Metrically, Holmes’s septets are erratic. Line by line, each stanza contains a line of pentameter, two of trimeter, another of pentameter, another of trimeter, and finally a line of hexameter. The alternating five- and three-beat lines imitate the nautilus’s toilsome, cyclical progression through its sequential chambers. The expansive hexameter of the last line expresses the nautilus’s final release, as figured in the poem’s final stanza.

At this point in the poem, the speaker is presumably peering inside the shell of the now-lifeless nautilus. The metaphor of the shell as a “sunless crypt” conveys both that the nautilus died within its own shell and that the opening of the shell represents a confrontation with a heretofore unglimpsed mystery, sunlight serving as an implicit metaphor for knowledge.

The image of the the nautilus shell as an “irised ceiling” is a double metaphor, comparing the shell to both an eye and a house. The eye metaphor touches on the literal reality of the nautilus shell, which encircles the nautilus’s eyehole in the way an iris encircles a pupil.

To imaginatively endow the nautilus with a “dim dreaming life” is to ascribe it a kind of consciousness, albeit a “dim,” unknowable one. In any event, the nautilus itself has died, leaving behind the biographical record of its shell and, for the speaker, subtle intimations of a consciously experienced existence. These intimations of consciousness form the foundation of the speaker’s encounter with the nautilus and give rise to the spiritual themes that take hold in the final two stanzas.

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.

The “webs of living gauze” refer to the method by which the chambered nautilus creates its shell, which involves the continual application of layers of aragonite. The metaphor of “gauze,” a thin linen fabric, suggests the gauzy translucence of the pearl shell. Having crashed ashore and died, the nautilus “no more unfurl[s]” its layers of shell.

In Greek mythology, the sirens were creatures who dwelled on a cluster of rocky islands in the Mediterranean Sea. They would lure passing sailors to the shore with their beautiful singing. Sailors who heeded the call would shipwreck on the treacherous coast. In this context, Holmes alludes to the sirens in an effort to imbue the poem’s setting with mythical wonderment as well as to draw on the dangers of the sirens. At the start of the next stanza, it is clear that the nautilus has suffered shipwreck.

The description of “purpled wings” flung “on the sweet summer wind” is likely an elaboration on the nautilus-as-ship metaphor, presenting the tentacles of the nautilus as the sails driving the ship forward. Complicating the metaphor is the implicit, nested connection between sails and wings. This metaphorical vision of nautilus-as-ship runs deep into the scientific record of the animal—so deep, in fact, that the selected name, “nautilus,” was drawn from the Greek word for “sailor”: nautílos. Evidently, Holmes was not the first to consider the nautilus in nautical terms. The shell is the ship, the mollusc itself the sailor.

A “bark” is a small ship. The word has become antiquated, though it emerges from the same root as “barge”—the Latin barca. In most modern usage, “bark” is employed to provide a touch of poetic flair.

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.

In a perplexing gambit, Holmes takes a self-referential turn in the very first line of the poem. After comparing the chambered nautilus to a “ship of pearl,” Holmes’s speaker pivots, saying “which, poets feign, sails the unshadowed main.” The phrase “poets feign” places the poem itself at a critical distance, questioning the validity of its own statements. Not only does the phrase recognize the poem as a poetic artifact, but also the word “feign,” which means “pretend,” points directly to the fictitious nature of all poetic works.

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.

Holmes’s “The Chambered Nautilus” serves as an example of a poem in which the title plays a critical role. The subject of the poem, as well as the tenor for all of its conceits and metaphors, is the chambered nautilus, an animal only ever named in the title. The first line of the poem begins with the word “This”—a pronoun pointing back to the title of the poem.