BRIEF [O.A.] Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 06.12.1891
BRIEF [O.A.] Hanitsch, Richard Author: Hanitsch, Richard Recipient: Haeckel, Ernst Corporation: Liverpool Biological Society, University College Dating: 19.12.1891
BRIEF [O.A.] Graff, Ludwig von Author: Graff, Ludwig von Recipient: Haeckel, Ernst Corporation: Zool.-Zoot. Institut der K. K. Carl-Franzens-Universität Dating: 02.02.1891