This represents the third volume of the series entitled Comparative PathobioZogy. The chapters included represent the proceedings of a symposium held at Oregon State University, Corvallis, on August 16-22, 1975. The symposium was co-sponsored by the Society for Invertebrate Pathology (SIP) and the American Society of Zoologists (ASZ). In recent years there has been an impressive increase in interest in comparative immunology, i. e., a comparative approach to understanding how animals, both vertebrates and invertebrates, defend themselves against nonself materials. Ever since Metchnikoff's...