Most endpapers in modern books are blank white pages, but they can be decorative, colored, or printed with something having to do with the contents of the book, as in the endpapers pictured here from a book called Spiders by Michael Chinery. The images of a multi-eyed beast marching across these pages depict "movements from the balletic courtship dance of a jumping spider." The author goes on to explain the spider's sex life, but you'll have to read the book for that. I'll just give you this little tidbit: "With both palps charged, the male is ready for action." Yow.
Here are some more examples of endpaper design:
|From Mother West Wind's Neighbors by Thornton W. Burgess (1913).|
|From A New Path to the Waterfall by Raymond Carver (1989).|
|From Trees, Shrubs and Flowers to Know in Washington by C.P. Lyons (1956).|
|From The Devil Wagon in God's Country by Michael L. Berger (1979).|
|From a German book called Michelangelo by Fritz Knapp (1907).|