A supplement to a laboratory exercise on motor units in crayfish abdominal ganglia, showing backfilled motor neurons, images of the ganglion, and videos of progressive serial sections through the ganglion in the transverse, sagittal and frontal planes. The serial sections and most of the other images were prepared by Brian Mulloney and Wendy Hall from the University of California at Davis. Higher resolution videos of the serial sections are available on their website: http://npb.ucdavis.edu/npbdirectory/mulloney_abdominal_ganglia/index.html.