The restaurant in the building at 9a In den Zelten was converted into a lecture hall after Hirschfeld acquired the building in 1921. The hall was named after Ernst Haeckel, whom Hirschfeld had greatly admired 1 3 .
Haeckel was a Social Darwinist and development biologist who spread monism, a new natural philosophy. The admiration shown Haeckel was typical of the enlightening spirit that prevailed at the Institute 2 . Research findings were passed on to members of both the working class and academia in evening classes and weekend and week-long workshops on sexual science 4 . The Haeckel lecture hall, with a supposed capacity of 200, was used for this purpose. In the spirit of the Enlighten-ment and humanism, reference was made to “spiritual giants”—quotations by Goethe, etc., were hung on the walls in and around the Institute—and famous scientists, whose signed portraits hung in the Institute stairwell.