Tonight “The Simpsons” makes television history. Roger Catlin at the Hartford Courant writes:

For a show that stars TV’s most prominent underachiever, “The Simpsons” has certainly reached some benchmarks.

It passed “The Flintstones” as longest-running animated prime-time show 10 years ago.

When its 18th season ends tonight with its 400th episode, it will be the longest-lasting comedy of any kind in prime-time TV history, surpassing “My Three Sons,” “M*A*S*H,” “Happy Days” and “Cheers.”

True, “[The Adventures of] Ozzie and Harriet,” which lasted 17 seasons, still holds the record for episodes produced: 435. But “The Simpsons” has a contract to go through a 20th season, when it will surpass that number in 2008.

“We have writers now who are so young that they grew up watching the show,” says show creator Matt Groening. “They remind some of us who have been around longer that we’ve already done a joke that somebody is pitching.”

The Courant has good sidebar links to “Simpsons” material, but you’ll find much more at “The Simpsons” website, which is pulling out all the stops for this milestone.

The graphic announcing the 400th episode at first just seems to be a cool image. But as you scroll over it, you realize that it’s interactive — profoundly interactive. And when you begin to explore a random episode — and then another one — you know you can’t help but lose a few hours to Simpsons nostalgia.

Tonight viewers can expect to see Ludacris making a cameo as “‘a tube of toothpaste that raps, of all things,” according to the AP. “The 29-year-old rapper-actor, whose real name is Chris Bridges, portrays ‘Luda-Crest’ in an informational video that brainy Lisa watches during the Simpsons’ annual dental checkup.”

All of which begs the question: Who’s your favorite cartoon cameo?