Internal Structure
Poems can either have "parts" or not. Sometimes these are visual structural divisions or they may be simply sections where things shift.
Poems with Parts
Internal structure: simile, theme, point of view, narration, etc.
Blackberry Eating, Galway Kindle Links to an external site.
Poems without Parts
These poems have no distinct sections, yet the structure still is deliberate as the poet had to choose some structure. There isn't a shift or a major change, yet, there is a a beginning, middle and end.
I Hear America Singing, Whitman Links to an external site.