While searching for scientific illustrations on Tumblr I noticed many were credited to the Biodiversity Heritage Library. I went there and discovered it is a website where research libraries from all over the world scan in books so that others may see and learn from them. Most of these books are very rare and many have wonderful illustrations.
The illustrations that follow are from Kunstformen der Natur (German for Art Forms of Nature). This book was published in 1904 and was illustrated by Ernst Haeckel, a German biologist who had a long, interesting, and prolific career as an artist and scientist. Here are just a few of the over 100 scientific illustrations in the book, that I chose especially for their particular visual and artistic appeal. The last one is my favorite (for now).