Title: Das ungelöste Welträtsel
Subtitle: Frida von Uslar-Gleichen und Ernst Haeckel
Subjects: Correspondence, Biologists, Friends and associates
Places: Germany
People: Frida von Uslar-Gleichen (1864-1903), Ernst Haeckel (1834-1919), Ernst Heinrich Philipp August Haeckel (1834-1919)