Dealing with sperm banks can be a costly exercise (costs can range anywhere from $300 to $4,000, according to the American Pregnancy Association)—especially if you're in the market for the highest quality sperm possible (aka, "college educated sperm that is free of disease and physical abnormalities"). But why deal with an intermediary when you can go straight to the proverbial sperm cow? That's the motto that Ari Nagel, a 40-year-old CUNY Kingsborough math professor, has ascribed to over the last decade. Nagel has donated sperm directly to 18 women over the last 12 years, producing 22 children. "I just love seeing how happy the moms and kids are...That’s why I do this," Nagel told the Post. "It’s the gift that keeps on giving."

The Post has a long, pun-laden front page feature on Nagel and his unique lifestyle ("Great Balls Of Sire"), chock full of eye-popping quotes, especially regarding the manner in which he transfers his sperm to the moms-to-be.

Apparently, about half the time, Nagel actually has sex with the women. He described one such scenario, in which the woman had her female partner in the bed with them for it: "She’s never slept with a guy before, so the partner’s in bed, holding her hand,” Nagel said. "Sometimes, it could be a little painful, then after a few times, they’re comfortable to do it on their own."

Lest you get the wrong idea, Nagel swears he isn't just trolling for hookups: "I’m not doing it for easy action," Nagel said. "Isn’t that what Tinder is for?" (For what it's worth, Nagel also is the proud owner of a still-live MySpace page.)

The other half of the time, Nagel meets with people in public places such as Target or Starbucks (he claims many of the women are more comfortable doing it in a public place rather than at his Downtown Brooklyn apartment), and then hops off to the bathroom to procure the sample. "It’s better when it’s fresh," he noted. "This isn’t time-consuming, and I’m doing it anyway. It’s very easy for me to do."

Nagel, who is very proud of his abnormally high sperm count (85 million per milliliter: "It’s off the charts...The clinic said they’ve never seen anything like it."), conceived his first child (who is now 12) with a woman he was in a committed relationship with. A few years later, he helped a single female friend conceive. And since then, he's met women through Craigslist, friends-of-friends and Known Donor Registry, a popular sperm donor website.

He apparently has a lot of happy customers: "He’s a lot of fun to be around, he loves people, he’s outgoing, and he’s gorgeous," says NJ resident Tiffany Harrison, 41, who with her wife, Yvonne, has a toddler daughter, Zoe, sired by Nagel. Nagel's name appears on the birth certificate for just under half of the children, a few families have used him multiple times, and there’s even an Ari Jr. and two Arias.

Not that it's all happy bathroom sperm donations for Nagel: the Post adds that the first five women he worked with "successfully sued him for child support, and nearly half of his paycheck is garnished for his offspring."

"I don’t know what’s more surprising: that five sued or that 17 didn’t," Nagel reflected. "They were all well aware there was no financial obligation on my part. They all promise in advance they won’t sue." Nagel doesn't regret the financial strains its caused: "Financially, it’s bankrupted me, but I’m still very happy with the way things turned out. I got 22 million in the bank — in my kids."

And as for his own love life, Nagel added that the women he dates don't mind his handy side business: "Never underestimate the desperation of a single woman on the Upper West Side," he said.