The German biologist Ernst Haeckel was fascinated by medusae, the umbrella-shaped animals commonly called jellyfish. For Haeckel, whose imagination was shaped in the Romantic era, medusae expressed the exuberant yet fragile beauty of Nature. And in their ethereal forms he glimpsed a reflection of his great love Anna Sethe, who died tragically at the age of twenty-nine.

Haeckel had been engaged to Anna for four years when, in 1862, he became associate professor of zoology at the University of Jena. The job gave the adoring pair the economic security they needed to finally marry. In the same year, Haeckel published a book on radiolaria (microscopic plankton) which he furnished with stunning illustrations. In Jena, the newlyweds lived together in bliss for eighteen months. Then, on the day he was supposed to celebrate his thirtieth birthday and receive an award for his radiolaria book, Anna died suddenly, probably of a burst appendix. Haeckel became mad with grief. A partial delirium kept him in bed for eight days. A month later he wrote to a friend, “I am dead on the inside already and dead for everything. Life, nature, science have no appeal for me. How slowly the hours pass.”

Haeckel travelled to the Mediterranean town of Nice to attempt a recovery from his suicidal malaise. One day he took a walk and saw a medusa in a rock pool: “I enjoyed several happy hours watching the play of her tentacles which hang like blond hair-ornaments from the rim of the delicate umbrella-cap and which with the softest movement would roll up into thick short spirals.” He made a sketch and named the species Mitrocoma Annae [Anna’s headband].

The grace and beauty of the medusa soothed Haeckel’s grief and contributed to what would be a lifelong fascination with medusae. In The Tragic Sense of Life, Professor Robert J. Richard describes the profound impact of Anna’s death on him:

Through this acid mist, Haeckel resolved to devote himself single-mindedly to a cause that might transcend individual fragility. He would incessantly push the Darwinian ideal and oppose it to those who refused to look at life, to look at death, face on . . . After a period of recovery, Haeckel abandoned himself to an orgy of unrelenting work that yielded, after eighteen-hour days over twelve months, a mountainous two-volume monograph that laid out his fundamental ideas about evolution and morphology.

As part of his efforts to demonstrate that all living things are interconnected through evolution, he produced monographs on Siphonophorae (1869–88), Calcareous Sponges (1872), Arabian Corals (1876) and Medusae (1879–81). A year after completing the medusae book, a mighty two-volume work describing 600 species, Haeckel had a house built in Jena. He named it Villa Medusa and decorated the ceilings with frescoes of medusae that would later appear as lithographs in his classic book Art Forms in Nature (1899–1904). When one day a colleague showed him a new medusa species that he found even more beautiful than Mitrocoma Annae, he had to name it after his first wife too. He called it Desmonema annasethe and produced a sketch that the lithographer Adolf Giltsch would turn into arguably the most famous plate in Art Forms (see first image featured below).

If you would like to see more of Haeckel’s mesmerising jellyfish, he published a two-part monograph dedicated to them full of wonderful imagery: those in part one's System of Medusae published in 1879 can be seen here, and those in part two, published in 1881, from reports of the British Challenger expedition (1873–76), can be seen here. Some decades later, in 1904, many medusae pictures (often based on Haeckel's earlier monograph images) were turned into stunning lithographs by Adolf Giltsch and published in the immensely popular Art Forms of Nature (see Prestel's 2008 edition here).

In addition to creating beautiful art, Haeckel held and promoted disturbing theories on race and eugenics. You can read more about this darker side to Haeckel in Bernd Brunner's essay "Human Forms in Nature". Also read about Haeckel's role in one of science's great controversies in Nick Hopwood's "Copying Pictures, Evidencing Evolution".