The bit of the ovary that fell out of the textbooks
Picture this. Scientists find a whole structure attached to the ovary. They draw it into the anatomy books. Then they shrug, decide it probably doesn't do anything, and quietly leave it out of later editions.
That is roughly what happened to the rete ovarii (say it "ree-tee oh-vair-ee-eye"). It was first described in 1870, appeared in early editions of Gray's Anatomy, got written off as a functionless leftover and then vanished from modern textbooks.
More than 150 years on, a research team led by women has gone back for a proper look. Turns out the rete ovarii is very much doing something, and what it does could change how we understand ovaries, fertility and conditions like PMOS (formerly PCOS), endometriosis and adenomyosis.
One thing before we get carried away: most of this research is in mice, so the human story is still being written. I'll flag what's known and what's a hunch as we go.
What is the rete ovarii?
Rete is Latin for "net", which is a fair description. It's a small network of tubes and cords at the base of the ovary, right where the blood vessels and nerves come in. In mice it has a curved, horseshoe shape.
The new research maps it into three connected parts:
- Intraovarian rete: thin, solid cords of cells tucked inside the ovary itself
- Connecting rete: the in-between stretch that joins the inside to the outside
- Extraovarian rete: a coiled tube sitting just outside the ovary and ending in a little bulb. Its cells have cilia (tiny hair-like sensors) and they release proteins
It isn't a quirk of mice either. The rete ovarii has been recorded across mammals, including cows, sheep, pigs, cats, dogs, monkeys, camels, guinea pigs and humans. When a structure sticks around in that many species, "pointless leftover" starts to sound like a guess.
Need a refresher on where everything else lives? Sexual Anatomy 101 has you covered, and vulva vs vagina is worth a read if school skipped that bit too.
Found in 1870, binned soon after
The rete ovarii was first described in 1870 by the German anatomist Wilhelm Waldeyer, when anatomy and medicine were almost entirely male professions. It earned a place in the drawings of early editions of Gray's Anatomy.
Then came the problem. Nobody could work out what it was for. So instead of "we don't know yet", the verdict became "it does nothing": a leftover from fetal development with no job in the adult body. Over the following decades it slipped out of textbook diagrams altogether.
Now compare that with its counterpart. The rete testis is the matching network in the testicles, and it has never had an identity crisis. It has a well-documented job moving sperm along and managing fluid on the way out of the testicle, and it has stayed in the books the whole time.
Two matching structures. One studied, one shelved.
To be fair, not everyone ignored it. In 1974, researcher Anne Grete Byskov asked in the journal Nature whether the rete ovarii helps trigger meiosis, the special type of cell division that makes eggs. The idea never made it into mainstream teaching, and the rete ovarii stayed a footnote for another 50 years.
The women who went back for a proper look
The comeback started with a microscope and a "hang on, what's that?" moment.
Dr Jennifer McKey, a developmental biologist then at Duke University in the US, was imaging whole mouse ovaries in 3D when she spotted a horseshoe-shaped structure at the base that her textbooks didn't mention. She went digging through old anatomy papers to find out what it was.
Dr Dilara Anbarci took it from there. Working in Professor Blanche Capel's lab at Duke (she's now at the University of Michigan), she made the rete ovarii her research focus. In March 2025 the team published Rediscovering the rete ovarii, a secreting auxiliary structure to the ovary in the journal eLife, with Anbarci as lead author.
Here's what they found in mice:
- Fluid flows towards the ovary. When the team injected dye into the tip of the rete, it travelled into the ovary, not away from it
- That fluid is packed with proteins. They identified thousands, including IGFBP2, which helps control the growth signals involved in follicle development (follicles are the little sacs that eggs mature in)
- It's properly plugged in. The outer section is wrapped in blood vessels, touched by nerve fibres and surrounded by immune cells called macrophages
- It listens to hormones. The rete responds as oestrogen levels rise and fall across the cycle
Anbarci's working theory is that the rete ovarii acts like an antenna: picking up signals from the rest of the body and relaying them to the ovary. Capel has suggested it could help decide how many follicles get switched on in a cycle, and when.
That is a long way from "functionless". The clue is in the paper's title: this is a rediscovery, and the team's argument is that the rete ovarii belongs back in the picture as a working part of the reproductive system. The textbooks have some catching up to do.
Could the rete ovarii matter for hormonal and gynae conditions?
Honest answer: maybe, and nobody knows yet. No study has linked the rete ovarii to any human condition.
But look at how many conditions involving the ovaries, hormones and womb medicine still can't fully explain:
- PMOS (polyendocrine metabolic ovarian syndrome) is the new name for PCOS, agreed in May 2026 and published in The Lancet. It affects around 1 in 8 women and it's a whole-body hormonal and metabolic condition, which is partly why the misleading "cysts" were dropped from the name. More in PCOS just got rewritten and the guide to symptoms, diagnosis and support
- Endometriosis and adenomyosis affect around 1 in 10 women. Amanda Haswell's endometriosis and adenomyosis explainer describes endo as a complex full-body disease that still lacks basic understanding, and she isn't exaggerating
- Fertility problems and early menopause, where there are still far more questions than answers about why ovaries do what they do. (See early signs of menopause and missed a period?)
Now look at what the rete ovarii seems to be doing in mice:
- It responds to hormones, including oestrogen
- It releases IGFBP2, a protein that mops up a growth signal called IGF1 (insulin-like growth factor 1). The researchers suggest this could work as a brake on follicle growth
- The team has proposed it may pick up on metabolic signals, such as insulin levels and changes in diet, and pass that information on to the ovary
- It's wired into nerves, blood vessels and immune cells, so it could be relaying messages from several body systems at once
Hormones, growth signals, metabolism, nerves and the immune system, all meeting at the ovary. For conditions we struggle to explain, that's a pretty interesting spot to have ignored for 150 years.
Science writers have floated possible links to PCOS, infertility and premature ovarian insufficiency, and a commentary in eLife points to possible uses in fertility preservation and treating ovarian disorders.
For endometriosis, the closest thing I can find is a small 1999 pathology study of human tissue. It looked at the rete ovarii partly because it can be mistaken for endometriosis under the microscope, and found it was far less responsive to oestrogen and progesterone than endometriosis tissue. So any link there is an open question, and it's a good reminder that mouse findings don't automatically carry over to humans.
What we can't say yet:
- That the human rete ovarii works the same way as the mouse one
- That it causes, worsens or protects against any of these conditions
- That anyone can test for it, scan it or treat it
Other scientists are keeping everyone's feet on the ground too. Developmental biologist Serge Nef, who wasn't involved in the study, told Science News this is only the start of the story. We still need experiments showing what happens to fertility without a rete ovarii, and proof that it works the same way in humans. Older studies suggest follicles can develop without it, so it may turn out to be a supporting act and not the headliner.
If you're living with any of these conditions right now, none of this changes your care today. What it does change is the questions being asked, and that's how better answers eventually turn up. If your cycle is doing something that worries you, the Is my period normal? quiz is a good starting point.
Why did it take 150 years? Medical misogyny and the funding gap
I'll be generous for a second. The Victorians didn't have 3D imaging or protein analysis. Fine.
But the tools to look properly have been around for decades, and the rete testis never had to wait for them. "We can't work out what it does, so it must do nothing" is a pattern in the history of bodies with ovaries, vulvas and wombs. It isn't a one-off.
- The full anatomy of the clitoris wasn't properly mapped until urologist Helen O'Connell's work in 1998. (More on that in 5 essential facts about the clitoris)
- The US National Institutes of Health only formally required women to be included in the clinical research it funds in 1993
- In the UK it takes an average of 8 years and 10 months to get an endometriosis diagnosis, and 78% of people surveyed said doctors had dismissed their symptoms. (Endometriosis and adenomyosis, explained)
- In December 2024, MPs on the Women and Equalities Committee named the problem outright: medical misogyny, with symptoms normalised, pain dismissed and big gaps in research, funding and clinician training
Follow the money
Research doesn't happen without funding, and the numbers here are grim.
- Women spend 25% more of their lives in poor health than men do
- Conditions specific to women, including endometriosis, menopause and PMS, make up 14% of that health gap but received less than 1% of research funding between 2019 and 2023, according to the same McKinsey Health Institute and World Economic Forum analysis
- Women's health received only around 6% of private healthcare investment between 2020 and 2025
This is what medical misogyny usually looks like. There's rarely a villain twirling a moustache. It's a long chain of "not a priority". Funding shapes research. Research shapes textbooks. Textbooks shape medical training. And at the end of that chain, someone sits in a GP surgery being told their pain is normal.
The rete ovarii is a small structure, but it tells that whole story. As Dilara Anbarci put it to Live Science: "There's still so much we can't even begin to comprehend about female anatomy."
A quick note on language. Most of this research talks about "women" and "female" anatomy, so I've kept those words where I'm reporting what a study or report says. All of it matters for anyone with ovaries, including trans and non-binary people.
So what can you do with this?
You don't need to do anything about your rete ovarii. It has been quietly getting on with things this whole time.
What this story is good for is a reminder that "we don't know" and "it doesn't matter" are two very different things, and that people with ovaries have been handed the second one far too often.
So keep asking questions about your body. Track what's normal for you (Period Tracking 101 is a good place to start). And if you've been told your symptoms are nothing and your gut says otherwise, you're allowed to ask again, ask someone else or take a friend with you. You can find clinics and charities near you in the sexual health directory.
Fancy more of the history they left out? Have a browse of the Sex Positive Library.
Rete ovarii FAQs
What is the rete ovarii?
A small network of tubes and cords attached to the base of the ovary. It was first described in 1870, dismissed as having no function, and is now being studied again after research showed it sends protein-rich fluid into the ovary and responds to hormones.
Do humans have a rete ovarii?
Yes. It has been recorded in humans and in lots of other mammals. What we don't know yet is whether the human version works the same way as the mouse one, because the detailed research so far has been done in mice.
Who rediscovered the rete ovarii?
Dr Jennifer McKey spotted it while imaging mouse ovaries at Duke University. Dr Dilara Anbarci then led the study that mapped what it does, working in Professor Blanche Capel's lab. Their paper was published in eLife in 2025.
Is the rete ovarii the same as the rete testis?
They're counterparts. The rete testis is the matching network in the testicles and helps move sperm and fluid along. The rete ovarii seems to do a different job, more like a sensor and messenger for the ovary.
Does the rete ovarii cause conditions like PMOS or endometriosis?
There's no evidence that it does. Researchers are curious because it appears to deal with hormones, growth signals, metabolism and the immune system right at the ovary, and those are all areas we don't understand well enough in conditions like PMOS, endometriosis and adenomyosis. That makes it worth studying. It doesn't make it a cause.
Can a doctor check my rete ovarii?
Not at the moment. It isn't part of any standard test, scan or diagnosis. If you're worried about your periods, hormones or fertility, the usual routes through your GP or a sexual health service are still the right ones.
Why was it left out of anatomy textbooks?
Because nobody could say what it did, and it was assumed to be a leftover from development. Add a long history of underfunding and under-researching female anatomy, and nobody went back to check for well over a century.
References
- Anbarci DN, McKey J, Levic DS, Bagnat M, Capel B (2025). Rediscovering the rete ovarii, a secreting auxiliary structure to the ovary. eLife, 13:RP96662. doi:10.7554/eLife.96662
- Zhang Y, Zhang H (2025). Ovarian biology: Revisiting the rete ovarii. eLife. doi:10.7554/eLife.106648
- Anbarci DN et al. Rediscovering the rete ovarii: a secreting auxiliary structure to the ovary (preprint, version 2). bioRxiv. doi:10.1101/2023.11.08.566085
- Willcoxon M (11 April 2025). An overlooked organ may help the ovary function. Science News
- ScienceAlert (28 February 2024). Ovary appendage dismissed as functionless may act like the organ's 'tongue'
- Tarita T (28 April 2025). Scientists rediscover a lost piece of female anatomy that may play a crucial role in fertility. ZME Science
- Glover A (21 September 2026). Rete ovarii: the female body part ignored for decades may be key for ovary health. HuffPost UK, via Yahoo News UK
- Bored Panda, via AOL (24 September 2026). This female body part was deemed useless and erased from textbooks, now scientists say they got it wrong
- Byskov AGS (1974). Does the rete ovarii act as a trigger for the onset of meiosis? Nature, 252, 396 to 397. doi:10.1038/252396a0
- Endocrine Society (12 May 2026). Polyendocrine Metabolic Ovarian Syndrome: new name to improve diagnosis and care of condition affecting 170 million women worldwide
- The Lancet (2026). Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: a multistep global consensus process
- Endometriosis UK (March 2024). "Dismissed, ignored and belittled": the long road to endometriosis diagnosis in the UK
- Women and Equalities Committee, UK Parliament (11 December 2024). 'Medical misogyny' is leaving women in unnecessary pain and undiagnosed for years
- McKinsey Health Institute and World Economic Forum (21 January 2025). Blueprint to close the women's health gap: how to improve lives and economies for all
- Euronews (25 January 2026). Women lose 75 million years of healthy life annually, yet receive only 6% of health funding (reporting a World Economic Forum and Boston Consulting Group analysis)
- O'Connell HE et al. (1998). Anatomical relationship between urethra and clitoris. The Journal of Urology
- Khan MS, Dodson AR, Heatley MK (1999). Ki-67, oestrogen receptor, and progesterone receptor proteins in the human rete ovarii and in endometriosis. Journal of Clinical Pathology, 52(7), 517. doi:10.1136/jcp.52.7.517
