BRIEF [O.A.] Frohwein, U. Author: Frohwein, U. Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 08.05.1912
BRIEF [O.A.] Melliess, W. Author: Melliess, W. Recipient: Haeckel, Walter Corporation: Bibliographisches Institut Dating: 18.02.1921
BRIEF [O.A.] Meyer, Hans Author: Meyer, Hans Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 27.11.1889
BRIEF [O.A.] Meyer, Hans Author: Meyer, Hans Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 06.09.1890
BRIEF [O.A.] Meyer, Hans Author: Meyer, Hans Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 21.03.1890
BRIEF [O.A.] Meyer, Hans Author: Meyer, Hans Recipient: Haeckel, Ernst Corporation: Bibliographisches Institut Dating: 16.11.1893