The bear that nobody measured

A true story in nine panels · no new experiments were performed

All the organs inside the translucent tardigrade

In 2019, a group of scientists put a water bear in a synchrotron and took the sharpest X-ray anyone had ever taken of one.

152micrometres, end to end

A living tardigrade stained with three fluorescent dyes

Then they published all of it — every voxel — under a licence that said: do what you like.

…and then almost nobody did.

The nervous system alone inside the body

Seven years later we downloaded it. Rebuilding the animal took an afternoon.

WHIRRR

Behind the brain sit four lumps of nerve, one per pair of legs. We went looking for their sizes in the paper and found this sentence: they did not measure them.

385ganglion one

The head, close: brain, first ganglion and stylets

So we measured them. You cut the cord wherever it gets fatter than ten square micrometres. The cables never get above six. The lumps never drop below forty-seven. No argument about where the knife goes.

385 · 430 · 379 · 194

1,386the four, added up

1,389the brain

Three cubic micrometres apart, out of fourteen hundred. We have no idea what that means and we are not going to pretend otherwise.

The animal cut across with the real X-ray on the cut face

Then we asked when it all gets built — using sixty-two embryos somebody else sequenced in 2016 and left alone. The genes that lay out the nervous system all fire together in a twelve-hour window. And one gene switches on 288 times over: this animal's version of the gene that decides, in a worm, which cell becomes which neuron. Nobody had ever found one in a tardigrade.

288×from nothing

The bit at the back where we admit things

One animal, dried out and fixed. Gene readings from whole embryos, so we cannot tell you which cells anything happened in. The ganglion sizes depend on where you put the knife — we tried every position from 8 to 25 and the numbers moved less than a tenth.

And a gene that looks like unc-86 is a reason to go and look, not a finding. We got a different one wrong last week and left the wrong version published next to the right one.