Ed Yong in The Atlantic:
In 2019, if everything goes according to plan, the much-delayed James Webb Space Telescope will finally launch into orbit. Once assembled, it will use an array of 18 hexagonal mirrors to collect and focus the light from distant galaxies. This segmented-mirror design was developed in the 1980s, and it has been so successful that it will feature in almost all the large telescopes to be built in the near future.
But as always, nature got there first. For millions of years, scallops have been gazing at the world using dozens of eyes, each of which has a segmented mirror that’s uncannily similar to those in our grandest telescopes. And scientists have just gotten a good look at one for the first time.
Yes, those scallops—the pan-seared pucks of white flesh that grace our dinner plates. Those pucks are just the muscles that the animals use to close their beautiful shells. Look at a full, living scallop, and you’ll see a very different animal. And that animal will be looking right back at you, using dozens of eyes that line the fleshy mantle on the inner edges of its shell. Some species have up to 200 eyes. Others have electric-blue ones.
Inside the eyes, the weirdness deepens. When light enters a human eye, it passes through a lens, which focuses it onto the retina—a layer of light-sensitive cells. When light enters a scallop eye, it passes through a lenslike structure, which … doesn’t seem to do anything. It then passes through two retinas, layered on top of each other. Finally, it hits a curved mirror at the back of the eye, which reflects it back onto the retinas. It’s this mirror, and not the lens, which focuses the incoming light, in much the same way that those in segmented telescopes do.