Monograph on the Medusae, vol 2, 1881, plate 1 ‘As a professor, he was beloved by his pupils, many of whom themselves became professors of biology around the world. They always described Haeckel as “a person one can only love”. But he had his enemies as a scientist, particularly in the Catholic church. He once said: “I am forced to react as I do.” He felt what he said and wrote was a reaction to the world. I’m not sure how true that was – but there were two different people in Haeckel, depending on who he was speaking to.’

Illustration: Taschen Köln/Niedersächsische Staats- und Universitätsbibliothek Göttingen