This is not to say that song was banished from Wagner’s world. Prior to The Ring, Wagner had written Tannhäuser, an opera revolving around a song contest. He would later return to the subject in The Mastersingers of Nuremberg, a five-hour opera about the power of the three-minute pop song: the young hero learns to master the art of songwriting, sings the song and wins the girl. (Of course he wins the contest too.)
But back to The Ring, and its music drama of unending melody, and no songs. Well, that was the theory. In Das Rheingold, the "introductory evening" of the drama, that's also the practice, but by the final day and Götterdämmerung, those pesky grand-operatic trios and chorus have crept back in. If one were tempted to pinpoint the turning point in this assimilation of traditional forms, one might look to a moment in the first act of Die Walküre, the First Day of the cycle (performed on the second night, as Das Rheingold was the Introductory Evening... are you keeping up?).
While Das Rheingold is concerned with the political wranglings of cloud-dwelling gods, subterranean dwarves and mermaid-like Rhinemaidens, Die Walküre turns its focus to humans. Boy meets girl. Girl is unhappily married to thug. Girl drugs thug. As he sleeps, boy and girl begin to articulate that they were, you know, meant for each other. But they are interrupted: not by the waking husband, but by the door flying open (with much noise in the orchestra), and an incoming flood of moonlight. The boy’s response is to sing for, oh, about three minutes, what sounds suspiciously like a pop song. Music-as-drama is put on hold and the poetic imagery is cranked up in a song of how "Spring" has awakened "Love". As the girl decodes his allegory - you are the spring - there is a seamless return to music-drama dialogue. But, tellingly, after three-quarters-of-an-hour of densely-argued drama, when the time came for a straight-out celebration of romantic love, Wagner chose to articulate this through song.