The Trio (no. 6, in the operetta's Scene 12 [of 14]) opens with a short theme "A table! A table!"—(as 8+ bars), followed by Gustave's chanson "Versez, versez"; then a scena follows, "Ah! maintenant cela va mieux," and Catherine's rondeau "J’en prendrai un, deux, trois." The rondeau will be discussed in the next post. For number list and synopsis see the introduction: link.
"Versez, versez" is a small ternary form. Catherine joins Gustave during the B-section, and all three players sing the reprise. In the A-section, the cadence is a turn to the dominant, from which the B-section follows directly.
Here is the reprise, showing in the first three systems only Gustave's part, the principal melody. Catherine is singing a simple mid-range accompaniment and Rabastens follows the bass line.
For the final bars, I show all parts below. Note especially that Catherine and Gustave trade scale degrees (voice exchange) and thus Gustave is able to go one-note-too-far to Bb4 (concert or actual pitch).