What does ‘calling for another boy’ mean?

I was reading an old Victorian novel in which some drinking companions called for ‘another boy’. What is the origin of the phrase?

The term ‘boy’ was simply a Victorian (and Edwardian) slang word used for a bottle of champagne. One day our descendants may be equally puzzled when they read about somebody having a ‘dop’. A grape-skin? An egg-shell? A lid? ‘Dop’ can mean many different things.