Because CBS' "Supergirl" comes from the same producers as The CW's "Arrow," "The Flash," and "Legends Of Tomorrow," it's only natural to wonder whether the two networks would allow crossovers. Back in August, CBS' answer was a pretty firm "no," although CBS Entertainment chairman Nina Tassler said the producers were "very inventive about what they can and will do."

RELATED: Place Your Bets: Who is Zoom, "The Flash's" Terrifying New Nemesis?

For example, "Arrow" just teamed up with John Constantine -- and specifically, the version of Constantine played by Matt Ryan on last season's short-lived NBC series. Strictly speaking, that wasn't a crossover. "Constantine" had already been cancelled, and the character was on "Arrow" helping out with the latter show's ongoing subplots.

Still, that cross-network appearance may have given Executive Producer Greg Berlanti and his fellow producers enough wiggle room to make some similar connections between the Arrowverse and National City. Therefore, here are a few more classic DC Comics characters (or groups) who could pop from one show to another, Constantine-style, and thereby bridge the gap between networks.

Deadman



Deadman is the ghost of Boston Brand, an ex-acrobat given the power to inhabit the living in order to solve his own murder. If that sounds like a good setup for a TV show, join the club.

It's basically a supernatural version of "Quantum Leap" with an ongoing who-killed-me? "mythology" arc. (It's also an inside-out version of "iZombie's" personality-borrowing schtick, but I digress.)

Anyway, Boston's quest to find the hook-handed killer could be dropped into any number of "Arrow" subplots, especially since the show has already established the League of Assassins and HIVE as go-to evil organizations. The character could also appear on "Supergirl" as a world-weary contrast to Kara's optimism. Not that the show lacks such contrasts, but there is a precedent for this particular pairing: the 1989 "Christmas with the Super-Heroes" story where the ghost of the pre-"Crisis" Supergirl inspired Deadman.

While that version of Kara doesn't quite match up with CBS', teaming up the two could demonstrate how Supergirl can pep up the downtrodden just as well as her cousin.

The Amazons





Yes, Wonder Woman belongs to the movies; but that hasn't stopped "Supergirl" from interacting with Superman, or "Flash" from mentioning WayneTech (albeit in a newspaper from the future). Full-on Amazonian action might have to wait until a time-traveling "Legends Of Tomorrow" team can visit Themyscira in its prime. However, depending on how each show wants to use them, the Amazons' various visits to Patriarch's World can be fairly flexible.

For example, setting them up as age-old counterpoints to the League of Assassins would allow one or more Amazon warriors to square off against "Arrow"'s Nyssa al-Ghūl. Similarly, the crew at STAR Labs might learn a few things from the super-science that created the Purple Ray and the Invisible Jet. Finally, "Supergirl" could show viewers everything from the Themysciran Embassy to Kara's learning more sophisticated fighting skills from an Amazonian coach.

Atlantis



If Jay and Caitlin just talked about it on "Flash," there's no reason why the Catco staffers can't bring it up as well. In this respect it's like Themyscira: in a world with a Metropolis, and where "National City" looks an awful lot like Los Angeles, it's a lot easier for an ancient undersea civilization to be just one more spot on the map. As for the Arrowverse, if they're going to spend that much time on Flashback Island, they're bound to encounter some weird things in the water, right?

There could even be competing versions of Atlanteans: the two-legged kind, like Aquaman; and the mer-person kind, like Superman's ex-girlfriend Lori Lemaris. This would actually be in keeping with DC lore, since readers wondered for decades about the distinction. (FYI, they're from two different approaches to surviving underwater, as pioneered by the cities of Poseidonis and Tritonis.) Heck, Lori herself seems like a natural for "Supergirl," since she could give Kara even more insight into her cousin's early years on Earth -- including the highs and lows of young lurve.

Teen(ish) Titans



Introducing Atlantis or the Amazons could lay the foundation for a very CW-friendly version of the Teen Titans (future TNT series notwithstanding). Robin is probably off the table, but "Arrow" has Speedy, and "Flash" may soon have Kid Flash. Bring in Wonder Girl and Aqualad, and you've got the core of the original Silver Age lineup. By teaming up its versions of Huntress and Black Canary, "Arrow" has already done a "Birds Of Prey" homage, and the show has borrowed enough "Titans" material (including Deathstroke and Brother Blood) that it might as well go all the way. Unless Aqualad or Wonder Girl comes over from CBS, it might not have a natural "Supergirl" connection, but it's still fun to contemplate.

Booster Gold



If Rip Hunter's set for "Legends of Tomorrow," Booster can't be far behind. He was in "Smallville," the "Arrow" producers have been trying to get him on TV for the past few years, and now Nathan Fillion wants to play him in a movie.

Before all that, however, Booster started out as a Metropolis-based hero whose emphasis on merchandising got him in trouble with Superman. Booster essentially highlights the more mercenary aspects of super-powers, leveraging his fame into paid endorsements and relying on his costumed career as a lucrative day job. I could easily see him coming to National City for new opportunities and sparring both with Cat Grant and his "Justice League International" buddy Max Lord; but I'm almost more eager for him to annoy the ever-loving pants off of Ollie Queen or the Earth-2 Harrison Wells.

The 31st Century



There is another, more indirect, far-future connection between the worlds of Supergirl and the Flash. Don and Dawn Allen, AKA the Tornado Twins, first appeared in a Legion of Super-Heroes story in 1968's "Adventure Comics" #373, as direct descendants of Barry Allen who gained super-speed for a "Flash Day" stunt. Much later, Dawn and Don were revealed as Barry and Iris' children, conceived during what turned out to be Barry's last few weeks of life, when he and Iris had relocated to the mid-30th Century just before "Crisis On Infinite Earths." The twins eventually became parents themselves: Dawn gave birth to Jenni "XS" Ognatz, and Don fathered Bart "Impulse/Kid Flash/Flash IV" Allen. XS joined the Legion, while Bart traveled back in time to meet his grandmother Iris and cousin Wally West.

Of course, Supergirl has been a member of a couple of different versions of the Legion, and the team showed up in the later seasons of "Smallville" without a lot of hassle, so it wouldn't take much to bring some Legionnaires (including XS) to National City. Just having Jenni acknowledge her super-speedy lineage might be enough to qualify as a stealth crossover. Likewise, the Tornado Twins could introduce Barry and Iris to familiar aspects of the future like Interlac, the United Planets, and R.J. Brande -- as well as assuring the Flash that not every time-traveling speedster is out to get him.

Zatanna




"Constantine" incorporated elements of DC's magical super-folk like Jim Corrigan and the Helmet of Fate, but for my money, Zatanna works best with both the Arrowverse and "Supergirl." If Team Arrow (or, for that matter, Team Flash) ever needs another magician, and Matt Ryan can't make it, Zee is certainly an option. In fact, for a very brief period following Iris Allen's death, Barry and Zatanna engaged in some harmless flirting in the pages of "Justice League."

Otherwise, "Smallville" showed how Zatanna's magical background could cramp a Kryptonian's lifestyle. "Supergirl" could go a little further, using Zee's celebrity -- to be sure, a more benign form than Booster's -- to help with Kara's public-relations struggles.

Project Cadmus



Bear with me, because this one is a stretch. The Newsboy Legion (created by Joe Simon and Jack Kirby) was a Golden Age group of street urchins who palled around with a cop named Jim Harper. Harper also had a costumed identity, the shield-wielding blue-and-gold Guardian.

When Jack Kirby took over "Jimmy Olsen" in the early '70s, he created Project Cadmus, a genetics-research laboratory, and brought back the Newsboys and the Guardian as youthful clones of their old selves. Naturally, Jimmy and Superman then teamed up with the new Newsboys and Guardian.

Here's the "Arrow" connection: Jim Harper, the original Guardian, was the great-uncle of Roy "Speedy" Harper. Accordingly, Speedy showed up in a 1970s "Superman Family" arc, working alongside Jimmy and the Newsboys. Therefore, "Supergirl"'s Jimmy could talk about adventures with the Newsboys and the Guardian, while Thea (or Roy, if he ever comes back) could bring up Roy's great-uncle as well. The shows wouldn't have to go any farther if they didn't want to introduce any more shadowy government agencies, but it would still be something in common. 

And finally...

The Green Lantern Corps







Look, it's clear that the producers of these shows want another crack at Green Lantern. Ollie's been to Coast City, Barry trained at an abandoned Ferris Air runway, and that shot of the unseen "Jordan" in the flight jacket wasn't exactly subtle. Hal Jordan and the GL Corps have deep connections to both Green Arrow and the Flash -- Hal went on that road trip with Ollie (which would make a fine flashback arc, hint hint), and he was one of Barry's best friends -- but I think the Green Lanterns should actually appear first on "Supergirl." After all, you'd think they'd want to investigate the Fort Rozz crash.

Moreover, with thousands of Lanterns available, "Supergirl's" GL wouldn't have to be Hal -- her reaction to Guy Gardner might put a new spin on "one punch!" -- and she wouldn't even have to be from Earth. A visit to National City from Katma Tui would open up the show to the rest of the galaxy, while keeping the Green Lanterns far enough removed that viewers wouldn't expect them every week. Kara could even ask the Guardians of the Universe "must there be a Supergirl?" Every Lantern is different, of course; but as long as they all seem to come from the same group, I'd say that counted as a connection.


Granted, while it's possible that any of these characters could show up on one network, I don't think it's especially likely for any of them to appear on both. Part of that is why I suggest using common organizations and locations -- because they can be vague enough to hint at connections without actually confirming them.

In just a few episodes, "Supergirl" has done an heroic amount of world-building, both in its on-screen depictions of National City and Krypton and in its many allusions to the people of Metropolis. That's allowed the show to distinguish itself fairly clearly from both "Arrow" and "The Flash." Moreover, "Supergirl" never lets its viewers forget that they live in a world with a Superman. That's the biggest distinction between CBS' super-show and its CW cousins, and it's an important one thematically. Currently "Arrow" deals in rejuvenating hot tubs, magical bad guys, and shrinking scientists, but it was a big deal for the show to embrace the idea of super-powered people. "The Flash," and by extension "Legends of Tomorrow," exist largely because "Arrow"'s producers decided to make that narrative leap. To reveal further that they all share the same world as Superman -- and particularly a Superman who's been around for quite a while -- might be too much at odds with the Arrowverse's more gradual development into "tights and flights."

Still, what kind of fans would we be if we didn't at least try to make these connections? Somewhere out there is a story where Mulder and Scully saved Cooper from the Black Lodge, or where Gary Seven and Roberta visited Gallifrey. Sometimes part of the appeal of these shows is the possibilities they create, regardless of whether those possibilities ever come to pass. Now if you'll excuse me, I have to get back to "'Office' Of Two Worlds..."