Dominicals

I am desirous of obtaining information on a subject of much interest to Exeter. An ancient payment is made to the rectors of each parish within the city of Exeter, called "Dominicals," amounting to 1*d.* per week from every householder within the parish. Payments of a similar nature are made in London, Canterbury, and I believe Worcester. Can any of your numerous readers state the origin of Dominicals, and give any information respecting them.