BRIEF OHNE UMSCHLAG Hertwig, Oscar Author: Hertwig, Oscar Recipient: Haeckel, Ernst Dating: 06.11.1889
POSTKARTE Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 02.09.1889
BRIEF OHNE UMSCHLAG Krukenberg, Gustav Author: Krukenberg, Gustav Recipient: Haeckel, Ernst Dating: 19.02.1889
BRIEF OHNE UMSCHLAG Kölliker, Albert Author: Kölliker, Albert Recipient: Haeckel, Ernst Dating: 04.08.1889