Before answering anything, click the following buttons to familiarize yourself with some terms and concepts of Schenkerian graphic analysis as applied to the "butterfly" subject.
Foreground: While every pitch is important, each derives its existence from the c-sharp with
which the fugue begins. Every pitch's importance derives from relationships with others.
1st Middleground
: Our immediate impression is of neighbor notes (N). M. 1 begins with
two neighbor clusters, and m. 2 with another. I've represented the neighbors in gray, and the
neighbor groups with broken-line ties , indicating prolongation of the main notes . In the
2nd Middleground we will drop the neighbors and represent their main notes with stems.
2nd Middleground : In this view passing tones (P) connect main notes by step. The diagonal
line is the unfolding symbol, which can be used to connect consonant skips, sometimes
involving "gap fill" (passing notes between). In the 3rd Middleground we'll drop the passing
notes and represent the low g# as a prefixed consonant skip in relation to the c# that follows it.
3rd Middleground : The pitches in gray are now heard as neighbors and consonant skips
(CS) in relation to the stemmed pitches (main notes). Notice how the first d#, now represented
as a suffixed upper neighbor, had been heard in the 2nd Middleground as a main note. Thus, a
pitch with high functionality at one level, derives its existence from something greater than it.
In the language of computer programming, the "parent object" (main note) of any diminution
may itself be the child object (diminution) of a more fundamental pitch.
Alternate View of the 3rd Middleground : The dotted ties indicate prolongation
of c#
and f#. Each prolongation involves one neighbor (N) and one consonant skip (CS), but in the
reverse order: MN-N-CS-MN becomes MN-CS-N-MN. Each contour retrogrades the other.
Background: At the highest level, the final E is the subject's goal. Although it is the goal,
E is nevertheless a consonant skip from the initial C#. The E is "prolonged" by a prefixed
incomplete upper neighbor.