Collection. The scalar collection represented in this passage is the 2♭ diatonic collection centered on C (i.e. C Dorian). In relation to the circle of fifths, the action has shifted one more click counterclockwise (i.e. down a fifth), and the pitch center has moved down two fifths, from the opening D, through G in the previous blocks, to C in this block. Within C Dorian, the two canonic melodies, C-B♭-A-G and F-E♭-D-C, are centrally located.