The Collins was most likely named after 19th-century bartender John Collins of London's Limmer's Hotel. The Tom Collins was originally made with Old Tom, a sweet style of gin that's extremely hard to find today.
In a pitcher, combine the limoncello, gin and lemon juice. Cover and refrigerate until chilled, at least 2 hours. Press 3 thin lemon slices against the inside of each of 8 collins glasses. Add ice to the glasses. Stir the limoncello mixture and pour it into the glasses. Stir 2 ounces of club soda into each drink and garnish with a mint sprig.