Some things can never be unseen. The microscopic mandibles of a fruit fly, for one. The leggy limbs of a hairy flea, for another. Three hundred and fifty years ago, scientist and amateur artist Robert Hooke’s exquisite illustrations of tiny things showed people for the first time what the parasites that plagued them looked like. In his 1665 book Micrographia—the first major work of illustrated observations made through a microscope—Hooke chronicled dozens of parasites, plants, and other microscopic wonders. The Royal Society will celebrate the book’s anniversary this Saturday with a microscopy drawing event and an exhibition in London. Robert Hooke was one of history’s most important scientists, coining the word “cell” and making profound contributions to timekeeping, astronomy, physics, and microscopy. He also argued, controversially in Micrographia, that fossils were the mineralized remains of ancient living organisms. We’ve learned a lot in the intervening centuries, but Hooke’s illustrations still inspire us to look closer.