It’s not unusual for Saturday Night Live to invite a guest host to do double duty as both guest host and musical guest – but it’s not often that SNL makes room for a guest host who also could double as a writer. Tonight’s host, Lena Dunham, certainly qualifies on that count, so expect her contributions to tonight’s new edition to be especially collaborative. And, of course, this is a great chance for her to get back at all the Girls critics who have complained about the show’s characters and body image issues. Musical guest: The National.