I discovered Ernst Haeckel's illustrations by doing some research about "Art Nouveau", a movement in the history of Art characterized by organic, especially floral and other plant-inspired motifs, as well as highly stylized, flowing curvilinear forms in the late 19th and early 20th centuries. I particularly like this movement and I'm amazed by Ernst illustrations, they are so detailed and subtile. He was a scientist and an inspiration for many artists from the "Art Nouveau" period.
Funny bat faces below. I would be scared if they were my friends.
All illustrations comes from the book "Kunstformen der Natur".