Here's the structure of this piece:
1. M. 1 - subject in the bass in the tonic
2. M. 3 - answer in the tenor in the dominant, counter subject in the bass (2 parts)
3. M. 5 - subject in the alto in the tonic, counter subject in the tenor (3 parts)
4. M. 8 - answer in the soprano in the dominant, counter subject in the alto (4 parts)
5. M. 14 - subject in the bass in the tonic, counter subject in the alto (3 parts)
6. M. 16 - subject in the soprano in the tonic, counter subject in the bass (4 parts)
Interestingly, this piece is written in the old Frygian mode because it ends on the E major chord and has no key signatures.
If you want to try your hand at creating (in writing or improvising) this kind of chorale fughetta, choose any kind of hymn tune, take it's first line, add a counter subject moving in faster note values in the intervals of major and minor thirds and sixths and follow the structure of BWV 696.