BRIEF OHNE UMSCHLAG Michelis, Heinrich Author: Michelis, Heinrich Recipient: Haeckel, Ernst Dating: 22.05.1906
BRIEF [O.A.] Michelis, H... Author: Michelis, H... Recipient: Haeckel, Ernst Corporation: D.M.B. Ortsgruppe Königsberg Dating: 21.10.1909
BRIEF [O.A.] Michelis, H... Author: Michelis, H... Recipient: Haeckel, Ernst Corporation: D.M.B. Ortsgruppe Königsberg Dating: 29.01.1914
TELEGRAMM Sack, G... Author: Sack, G... Recipient: Haeckel, Ernst Corporation: Taube (Zeitschrift) Dating: 16.02.1904