The Harvard University Police Department (HUPD) has increased security at William James Hall in recent weeks in response to continual protests and anonymous threats directed at an animal enclosure on the 10th floor.

In a related development, nearly 50 animal rights protesters marched through the Square Saturday, urging Harvard to release its captive monkeys.

Protesters have focused on a 10th-floor complex, the Primate Cognitive Neuroscience Lab, where 17 cotton-top tamarins and six vervet monkeys are held captive for research.

Professor Marc D. Hauser, who was tenured last year in psychology for his groundbreaking work in the field of animal cognition, directs the lab and its staff of more than 30.

Two veterinarians help care for the monkeys.

Hauser was not available for comment yesterday afternoon.

According to his lab's website, all of the experiments performed are non-invasive--that is, the animal is not killed or physically harmed. Many tests involve visual perception and audition, investigating the ways in which non-human primates decipher sensory stimuli.

But animal rights activists protest the captivity, saying that animal development is impeded.