What are the motifs in My Last Duchess by Robert Browning?

Art and experience is a recurring idea in the story. The Duke's monologue both begins and concludes with the Duke drawing his listener's attention to works of art: first, the painting of the "last Duchess," his former wife; in the final lines, a sculpture of the sea-god Neptune taming a "seahorse." Because of this, the entire monologue-ostensibly about the failings of the late Duchess-is actually couched in the aesthetic terms the Duke applies to human relationships. But precisely what are those terms? On one level, they seem wrapped in the same corrupt arrogance that led to the demise of his first wife.