Your ovaries have a neighbour. Most textbooks dropped it.

The rete ovarii appeared in anatomy drawings for decades, then disappeared. Mouse research now shows it is active, and raises a question nobody can answer yet for women.

The rete ovarii is a small network of fine tubes attached to the ovary. It was first described in 1870, appeared in early editions of Gray’s Anatomy, and later dropped out of recent textbooks because nobody could say what it did [1]. A 2025 study in mice found that it persists into adulthood, releases proteins and connects to nerves, blood vessels and immune cells [1]. Whether it works the same way in women is not yet known.

Most people have never heard of the rete ovarii. For a long time, the textbooks agreed with them.

First spotted in 1870, then labelled useless

The anatomist Wilhelm von Waldeyer described the rete ovarii in 1870 [1]. It arises from tubes that form early in the embryo, in the same way as its male counterpart, the rete testis [1]. In males, that network carries sperm out of the testis. In females, nobody could point to an equivalent job.

Drawings of the rete ovarii appeared in early versions of Gray’s Anatomy [1]. With no clear function, it was labelled vestigial, a biological leftover from earlier development. It was later removed from recent textbooks, and it came to be dismissed as a functionless vestige in the adult ovary [1]. Attention moved on.

Three parts, one network

The rete ovarii is a single connected network made up of three distinct parts. It starts just outside the ovary, passes through a middle transition zone, and reaches deep into the inside of the ovary. The outer part is a convoluted tubule that ends in a small bulb. The middle part connects the two. The inner part is a fine mesh of thin cell cords inside the ovary [1].

Until recently, no one could say what each part does

Anatomists have long known what the three regions look like. What they could not say was whether each one had a different job. Earlier work relied mostly on imaging thin slices of tissue, which shows shape and says little about activity [1].

Learning about each cell’s job

Researchers in Blanche Capel’s lab at Duke, including Dilara Anbarci and Jennifer McKey, used RNA sequencing on mouse tissue to find out. The method reads which genes are switched on in individual cells, so you can see how one cell differs from the next. It is a way of asking each part of the structure what it is doing.

The team sequenced cells from the mouse ovary and its surrounding tissue, both before birth and at two months of age, and found a gene called Krt8 that marks the rete ovarii [1]. A second clue came from the male side: a gene called GFRa1 is active in the rete testis, so they checked whether it was active in the rete ovarii too. Part of it was [1]. The team also released bulk and single-cell datasets of the mouse rete ovarii so other researchers can build on the work [2].

What the mouse experiments suggest

Early results point towards a secretory role. In mice, fluid from the outer region flowed towards the ovary, and it carried proteins that may matter for ovarian function [1]. One protein that stood out was IGFBP2, which can regulate growth factors linked to the formation of egg follicles [5]. Cells in the rete ovarii also switch on genes for hormone receptors, including those for estrogen and progesterone, at key times in the reproductive cycle [5].

Anbarci and colleagues propose that the structure works like an antenna, picking up hormonal and nerve signals and responding by releasing proteins into the ovary [5]. Adam Taylor, an anatomy professor at Lancaster University who was not involved in the study, told Live Science that the structure may help maintain the ovary and its environment [5]. Serge Nef, a developmental biologist at the University of Geneva, called this the beginning of the story. The open question is whether the rete ovarii matters for ovarian function at all [5].

What this does not tell us yet

All of this comes from mice. The rete ovarii is found in many mammals, from cows to monkeys, and it has been described in humans, but what it does in women is unknown [1][5]. Researchers hope to examine the structure’s effect on fertility, including whether shutting it down would change it [5].

Why basic anatomy matters

Research like this gives us the blueprint for what “normal” looks like. After all, you can’t spot the malfunction until you know how the system is supposed to work.

The rete ovarii is also a small example of what happens when a structure is labelled unimportant before anyone tests it. Anbarci put it plainly in an interview with Science News: “There’s still so much we can’t even begin to comprehend about female anatomy” [5].

What this means for research on women

Mouse findings are a first step. They tell researchers where to look, and they have to be confirmed in humans before anyone knows what they mean for women. Studies in women come later, and they depend on women taking part. At TrialMe, we explain how research works and help women find studies that fit their health and their lives.

FAQs

• What is the rete ovarii?

  A network of fine tubes connected directly to the ovary, with three regions: one inside the ovary, one outside it, and a connecting region in between.

• Is this a new discovery?

  No. It was first described in 1870. It was later considered functionless, and mouse studies in recent years have re-examined it.

• Do women have one?

  The structure has been described in humans. Most recent studies are in mice.

• What does it do?

  In mice, the evidence suggests it secretes proteins and moves fluid towards the ovary. In humans, its function is unknown.

• Does it affect fertility?

  That is not known. Researchers think it may play a role in how the ovary works, and they still need to test whether fertility changes when it is removed or shut down.

• Does this change anything for patients today?

  No. This is basic research. It is not a test, a diagnosis or a treatment.

• What is single-cell RNA sequencing?

  A method that reads which genes are switched on in each individual cell. It shows how one cell differs from the next.

• Why were mice used?

  Tracking fluid flow in real time is not possible in people. These mouse findings are a first step, and they have to be confirmed in humans.

Sources

1. Anbarci DN, McKey J, Levic DS, Bagnat M, Capel B. Rediscovering the rete ovarii, a secreting auxiliary structure to the ovary. eLife. 2025;13:RP96662. https://elifesciences.org/articles/96662v1

2. Anbarci et al. Bulk and single-cell datasets of the mouse rete ovarii. Scientific Data. 2024. https://www.nature.com/articles/s41597-024-03227-x

3. eLife Insight, “Revisiting the rete ovarii” (further reading): https://elifesciences.org/articles/106648

4. Science News, “An overlooked organ may help the ovary function” (further reading): https://www.sciencenews.org/?p=3153125

5. ZME Science, “Scientists rediscover a lost piece of female anatomy that may play a crucial role in fertility”: https://zmescience.com/science/news-science/scientists-rediscover-a-lost-piece-of-female-anatomy-that-may-play-a-crucial-role-in-fertility