POSTKARTE Gumprecht, Ferdinand Author: Gumprecht, Ferdinand Recipient: Haeckel, Ernst Dating: 03.02.1895
BRIEF OHNE UMSCHLAG Ammon, Sophie von Author: Ammon, Sophie von Recipient: Haeckel, Ernst Dating: 05.02.1909
BRIEF [O.A.] Ashcroft, Edgar A... Author: Ashcroft, Edgar A... Recipient: Haeckel, Ernst Dating: 27.01.1905