In the middle of one of Professor Alexander Nemerov’s GRD ’92 packed “Introduction to Art History” lectures on a Wednesday afternoon last month, a student dressed in a gorilla costume barged through the door of the Law School auditorium, grunting as he entered.

When the gorilla-man finally joined Nemerov on stage and offered him a banana, the professor stared sternly. Dejected, the gorilla exited the room, and Nemerov simply picked up where he left off without missing a beat. The class responded with peals of laughter.

But Nemerov, known for his pensive demeanor and ability to deliver lectures without notes, did not find it funny. Reflecting on the incident, he said the only thing to do in such a situation is to be silent.

“This is certainly not why I came to Yale,” he said. “I am very serious when I say it mocks the central purpose of the University.”

Nemorov’s class — with 330 students — has been interrupted three times this semester by various pranksters. Besides the gorilla, his class has had to deal with two female students teaching the proper way to mix a martini and a staged argument between a male and female student who was wearing a pillow under her shirt to appear pregnant. While such stunts are a perennial feature of fraternity and secret society initiations, professors and administrators are fed up.

In a campuswide e-mail sent Monday, Yale College Dean Mary Miller said the number of “staged disruptions” has increased this year, especially over the past few weeks. She emphasized that any such act is a violation of the Undergraduate Regulations and is subject to disciplinary action.

Nemerov said such interruptions send the message that his course is not important, and that its subject is not serious.

“Since I think it matters a great deal, that is really insulting to me,” he said.

Nemerov is not the only professor who feels this way. Recent complaints from a number of faculty members and one student prompted Miller’s e-mail, Dean of Undergraduate Education Joseph Gordon said. He said Yale is unique in having distinguished professors teach undergraduates to begin with, adding that the pranks may undermine the faculty’s willingness to teach in the demanding lecture format.

In her e-mail, Miller said faculty members have the right to conduct their classes without interference and students enrolled in these courses have the right to attend and participate in these classes without disruption.

“In a university dedicated first and foremost to teaching and learning, such intrusions cannot — and will not — be tolerated,” Miller said.

While Gordon said he is not aware of any recent cases of class disruption brought before the Executive Committee, the disciplinary body of Yale College, he said such actions clearly violate chapter one of the Undergraduate Regulations. ExComm Secretary Jill Cutler said no prescribed penalty exists for students who interrupt courses, but she said students who interrupt lectures would be seen by ExComm and held accountable for their behavior.

Chapter one of the regulations states that “participation in any effort to prevent or disrupt a class or other University function, or to seize or occupy any University building or part thereof, or to violate the right of an audience to listen at a University function” will be handled by ExCom.

For the most part, large introductory lectures are hit hardest by the initiation rites of campus organizations, said economics professor Timothy Guinnane.

Just last Thursday, two pranksters entered the Sheffield-Sterling-Strathcona Hall auditorium and grabbed a dildo handed to them by a female student sitting in the audience, said Pablo Cuevas ’13, a student in the class. The two proceeded to preach the importance of practicing safe sex while demonstrating the proper technique of applying a condom on the object. Guinnane let the duo finish, stating: “You can never have too much sexual education,” Cuevas recalled.

But as a result of these pranks, Guinnane said he and his colleagues in the Economics Department have grown tired of having to deal with the interruptions and even question the quality of the humor they provide. Guinnane, whose introductory microeconomics course during the spring semester has about 230 students enrolled, said he has been disturbed by two interruptions this semester.

In March, Guinnane’s class was paid a visit by a student dressed in a gorilla suit. When the gorilla-man did nothing after taking a seat in the audience for a few minutes, Guinnane took out his camera-phone, snapped photos and dismissed him by telling him he was “being disruptive only for the sake of being disruptive,” Cuevas said.

“I’m not adverse to pranks,” Guinnane told his students after the gorilla left. “Only bad ones.”

“If pranks are going to be a part of an initiation rite,” he elaborated in an interview, “they shouldn’t harm academics or students.”

He said pranks in recent years have become increasingly drawn-out, offering little real humor. Such interruptions were never acceptable, he said, adding that he believes the pranksters are cowardly because students often come in disguise before professors who don’t recognize them, bolstered by the belief that their classmates will not rat them out.

“Under the best of circumstances it’s a chore to keep class going,” Guinnane said. “But when someone comes in and interrupts it completely undermines what the professor is trying to accomplish.”

Steven Berry, whose introductory economics class was the most oversubscribed course at Yale during the fall semester, has been hit three times by pranksters this year.

“If pranks were short, rare and funny, then they might actually be a welcome break,” Berry said in an e-mail. “However, [they] seem to be increasingly long, frequent and disruptive.”

Now, Guinnane said he and some of his colleagues are discussing responses to prevent further disruptions next year. Among these include a zero-tolerance policy where if another prank occurs, the professor will turn off his presentation, leave the classroom and end class.

But not all faculty members necessarily share this sentiment.

After his popular Cold War lecture was repeatedly pranked in the fall of 2008, history professor John Gaddis actually lamented the unexplained disappearance of the Pundits prank society the following year.

“I missed you guys,” he said in his final lecture of 2009. “What happened?”

Then, in February, Gaddis’s “Art of Biography” seminar was interrupted by an extensive reenactment of the film “Titanic,” replete with cardboard cutout lifeboats and champagne in Solo cups.

In an e-mail, Gaddis said his classes have not been interrupted in the past few weeks.

William Summers, whose popular “Biology of Gender and Sexuality” (better known as “Porn in the Morn”) attracted a variety of pranksters before he stopped teaching it this year, said he has never found the interruptions to be a problem. He said they have not been prolonged, threatening or offensive, adding that the pranks are “really just a bit of silly humor that I have been able to accept in the spirit intended.”

In some ways, such tasks have merit, said Malay Araya ’10, who interrupted Summers’ course when she was a junior as a requirement of society tap. She strode into the lecture hall with members of her tap class and distributed condoms to students in the audience. She said the humiliating and public nature of such pranks brings the tap class together, adding that she thinks it is appealing to pull a prank in a lecture hall because its boldness walks the line of outright rudeness.

The Pundits, for their part, deny involvement in the recent course disruptions. As one member said in an e-mail, “Over this past week, sh—- societies forced their fledglings to perform sh—-, disruptive tasks, because nothing ritualizes society membership like a ton of awkward. The pundits refused to comment, before they vomited on everyone’s face.”

But with only four weekdays before the beginning of reading week, professors and administrators can rest easy — at least until next year’s tap.

Lauren Rosenthal contributed reporting.