BRIEF OHNE UMSCHLAG Keller, Conrad Author: Keller, Conrad Recipient: Haeckel, Ernst Dating: 03.01.1887
BRIEF OHNE UMSCHLAG Dodel-Port, Arnold Author: Dodel-Port, Arnold Recipient: Haeckel, Ernst Dating: 27.12.1887
BRIEF [O.A.] Beglinger, Johannes Author: Beglinger, Johannes Recipient: Haeckel, Ernst Dating: 23.01.1887
POSTKARTE Rottenburg, Paul von Author: Rottenburg, Paul von Recipient: Haeckel, Ernst Dating: 29.07.1887