Identify an extended metaphor in whitman's "song of the open road." in 300 words or less, explain how it develops over the course of the poem, and how it supports the poem's major themes.

His poem shows more structure than many of Whitman’s works. From the cry of "Allons!" (Let’s go!) that opens many of the stanzas, to the lists and repeated phrases (the "efflux of the soul," the "fluid and repeating character") this poem truly does have the character of a song: musical and rhythmic, while at the same time completely unconventional.