This collection contains sixty-four large scientific illustrations used by Joseph Leidy while teaching zoology at the University of Pennsylvania. The diagrams depict microorganisms and invertebrates namely protozoa, mollusks, annelids, crustacea and sponges. Some illustrations were drawn by Leidy or copied by him from textbook figures, while others were copied from texts by students under Leidy's supervision. Some diagrams are signed by Leidy and most bear his handwritten legends and notes. Leidy marked diagrams with "Aux. Med. Dep." or "Aux. Dep. Med." when used for lectures in the University of Pennsylvania's Medical Department.
