With an audacious display of whimsical excess that far outdoes schlepping an iceberg from Sweden, as Chanel did last March, Marc Jacobs, in what is heavily rumored to be his last collection for Louis Vuitton, puts a rotating merry-go-round on his runway. Models ride the carousel horses — pale lacy princesses of loveliness, like a dreamy little girl’s vision of what a Paris fashion show is like. If this is an audition for Dior, then Jacobs (who gets away with this sort of overspending, because, a colleague suggests, he has a punk heart) is proving that he is ready for his couture close-up. (On the other hand, how long can couture itself last? The feeling that we are dancing — or at least staring at clothes — on the head of a volcano gets stronger every day.)

Then again, maybe Marc won’t get the job. Maybe it will go to Haider Ackermann, whose name has also been floated, and whose slow-moving show features, along with iridescent mechanics’ jumpsuits and a host of excellent oversize jackets, a soundtrack of Antony and the Johnsons crooning John Lennon’s "Imagine." (“Imagine no possessions?” You first, John.) The guy you don’t want to be is Bill Gaytten, the current Dior designer, who offers a serviceable if lackluster collection hardly commensurate with the fuss and bother it takes to get into the Rodin Museum, where the show is held. But can you blame him? Sidney Toledano, the company’s CEO and Gaytten’s boss, has proclaimed that some kind of Dior announcement is due in a few weeks, and you know it’s not that Bill is going to keep his job. I mean, how zippy would you feel?

If L.V. represents a spun-sugar reverie, Sarah Burton’s Alexander McQueen collection could be the musings of a naughty little bad seed, counting the days until she can break free from her childhood bedroom and put on a sexy mask. The show takes place in the nineteenth arrondisement (who even knew there was a nineteenth?), and you’re sure you’re at the right place when you see a pair pf conjoined brides hanging out by the entrance, posing for pictures. The collection is staggeringly lavish and lovely, especially for those who want to play the occasional dangerous game of flaunting a golden peplum, but I can live without the masks that cover a model’s entire face — what is with the persistence of this notion anyway? Can’t her mouth at least be free?

Fashion, you will come to realize after many weeks of runway shows, is a serious business, the frivolity and glamour all but imperceptible under an avalanche of invoices and deadlines. So when a show is actually fun to watch it can really buoy the spirits. Unfortunately for Jean Paul Gaultier, the heat and delay fray the patience of many viewers at his wonderful presentation, which is styled like an old-fashioned catwalk show — the sort of thing you see in Clare Booth Luce’s 1939 The Women, and is exuberantly narrated almost entirely in French by a locally celebrated TV weather-woman. It is among the best J.P.G. collection in years, and the clothes include the designer’s special tropes ̬ lingerie detailing, trenches, tattoo motifs. To further crank up the vintage verisimilitude, the model’s hair is tightly rolled in a style last popular around 1939 as well. (A terrible year, but never mind.)

No extreme temperatures mar the cheeriness at Kenzo, which has been given to Opening Ceremony retailers Humberto Leon and Carol Lim to re-imagine. The runway is Crayola-bright, live drummers bang away to "Girls Just Want to Have Fun," the sunny clothes include a pair of comically oversize palazzo pants, and a newly brunet Chloë Sevigny closes the show. As you exit, pretty attendants hand out bags of cookies shaped like letters — I don’t lay them out, but I assume they spell Kenzo — to wolf down as you wend your way through the Palais Royal, under the spell of a spookily bright Paris moon.

See the Complete Louis Vuitton Spring 2012 Collection
See the Complete Haider Ackermann Spring 2012 Collection
See the Complete Christian Dior Spring 2012 Collection
See the Complete Alexander McQueen Spring 2012 Collection
See the Complete Jean Paul Gaultier Spring 2012 Collection
See the Complete Kenzo Spring 2012 Collection