Illustration from The Malay Archipelago (1869), depicting the flying frog Rhacophorus nigropalmatus discovered by Alfred Russel Wallace (1823-1913), the British naturalist, explorer, anthropologist, biologist, and geographer.

Ernst Haeckel: Kunstformen der Natur (1904, Artforms of Nature).

Ernst Haeckel (left) with fellow field biologist, Nicholi von Miclucho-Maclay. Canary Islands, 1866.