The campaign to free two chimpanzees from a lifetime of biomedical experimentation — and earn them recognition as legal persons — has taken a big step forward.

On Monday, Manhattan Supreme Court Justice Barbara Jaffe issued a summons for Stony Brook University to appear before the court in May. Stony Brook, which is holding the two chimps named Hercules and Leo in its labs, will have to prove that it's holding the chimps justifiably and that a petition to free them filed by the Nonhuman Rights Project should be turned down.

The move is significant because it's the first time that a motion to recognize chimps as legal persons — and therefore to allow them to benefit from legally protected bodily autonomy — has been acknowledged so directly in a court.

The NhRP originally said that Justice Jaffe's summons were a writ of habeas corpus, which can be issued only if the detainees — in this case, the chimps — are legal persons. The order therefore implicitly recognized the two chimps as legal persons and set a precedent for future petitions, the NhRP said in a statement on Monday.

However, this classification was debated. While many outlets — including The Dodo — originally referred to the summons as such, Justice Jaffe issued an updated order on Tuesday with the words "writ of habeas corpus" manually crossed out.

Matthew Liebman, senior attorney for the Animal Legal Defense Fund, said that the summons will serve a similar purpose to a writ of habeas corpus whether or not that's what the order is called. The salient point, he explained, is that Justice Jaffe actually called Stony Brook to a hearing — and that hearing will determine what happens to the chimps.

"I do think it's significant that she's taken the step of ordering them to come forward and justify the detention," Liebman said. "But it's a step and not the end."

The upcoming hearing could mean big changes in the lives of these captive chimps. It's unclear what conditions Hercules and Leo are living in, and NhRP — which refiled the petition to free them in late March — hopes to secure them the right to happily live out their days in a Florida primate sanctuary.

Natalie Prosin, executive director of NhRP, made clear that "personhood" is different than declaring chimps people, and that her group was looking only for one specific right that legal personhood would grant — rather than the "infinite" number of rights humans enjoy. "People get confused," she said. "We're just asking for a very fundamental right, which is the right to bodily liberty."

And if these two chimps are granted freedom at the upcoming hearing, that decision — and its inherent recognition of primates as nonhuman persons — could mean a world of changes for the thousands of primates currently kept in labs and zoos around the country, as recognizing them as persons could entitle them to a whole host of protections they don't currently enjoy.

"They are autonomous, self-aware and self-directed individuals," Prosin said of the chimps. "And their autonomy is not being respected since they are classed as property."

However, similar legal rights for other animals could be much further off. According to Prosin, there's no scientific evidence that would hold up in court to support the autonomy of animals besides great apes, elephants and cetaceans. "Those are the ones that we're focusing on," she said.

This story has been updated to include details about Justice Jaffe's revised order, as well as quotes from Matthew Liebman and Natalie Prosin.