"Nautilus pompilius LS" by David Bygott, used under CC BY / Cropped from original
"Mathematics *Explore April 24, 2013 #4* (at one time)" by Tom Brown, used under CC BY / Desaturated from original
"Mathematics *Explore April 24, 2013 #4* (at one time)" by Tom Brown, used under CC BY / Desaturated from original