Mr Beveridge's Maggot is an English country dance (Playford) from 1695. It has been made rather famous by the films Pride and Prejudice and Emma, in which the dance is done at a ball. Mara Shea (violin) and Julie Gorka (keyboard play the tune as it is danced in Pride and Prejudice, with the structure AAB. (A maggot, by the way, is not an insect here; it is a bit of whimsy or silly extravagance, in this context.)