This is the introductory volume of a new series to be issued under our general editorship. With the development of an unpre cedented increase in interest in comparative pathobiology, we are of the opinion and intent that Comparative PathobioZogy should become the focal point for the publication of definitive reviews and the proceedings of significant symposia in this area of modern biomedical science. Although the term is now in common use, the question is still sometimes raised as to what "pathobiology" includes. This broad area of modern biology includes but extends beyond traditional pathology. It also encompasses studies directed at understanding the biology, chemistry, and physics of infectious agents, in cluding how they contact and invade the effected organism; the reactions of hosts to such agents, as well as to abiotic invaders; the ecologic parameters which facilitate infection; and the development of tools essential for the understanding of hast pathogen interactions. In other words, pathobiology is inter disciplinary and incorporates all of those aspects of biology, chemistry, and physics which directly or indirectly permit greater understanding of the nature of infectious and noninfectious diseases and the possible implications of such in biomedicine, agriculture, and environmental science. By "comparative" is meant an analytical and critical evaluation of comparable processes as they apply to all categories of animals, invertebrates as well as poikilothermic and homeothermic verte brates."

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 pioneering studies during the late l800s on the role of phagocytes of invertebrates, which led to his theory of cellular immunity, invertebrates have been employed with increasing fre quency for studying cellular defense. Consequently, it is not surprising that included in the memberships of SIP and ASZ are a large number of individuals with an active interest in this area of research. As indicated by the chapters included in this volume, the animal models employed have been primarily molluscs and insects, although crustaceans and annelids have also been popular."

At a recent meeting of the Society for Invertebrate Pathology, Dr. K. Kanungo of Western Connecticut State University organized a special symposium on the topic of invertebrate circulatory systems with emphasis on hemocytes and their role in internal defense. The contents of this volume of Comparative Pathobiology represent the proceedings of that gathering. As the Editor of the Journal of Invertebrate Pathology, I am intimately aware of the current popularity of research pertaining to invertebrate immune mechanisms of which hemocytes and associated molecules play a central role. Consequently, the contributions in cluded herein should prove to be of interest to a variety of investi gators including invertebrate zoologists, comparative immunolo gists, physiologists, and cell biologists. As has been stated in previous volumes of this series, Comparative Pathobiology is meant for the publication of proceedings of symposia devoted to some aspect of that broad spectrum of modern biology known as pathobiology. Those interested in having antici pated contributions considered for publication should contact me."

On August 21-26, 1977, two symposia were included in the program of the 10th Annual Meeting of the Society for Invertebrate Pathology held at Michigan State University, East Lansing, Michigan. One was entitled "Invertebrate Models for Biomedical Research" organized by Dr. Thomas C. Cheng, and the second, organized by Dr. Robert S. Anderson, was entitled "Cellular and Humoral Reactions to Disease by Invertebrate Animals." When the final manuscripts of the speakers were received, it became apparent that all of the papers were so closely related that the editors decided that they should be combined and published in a single volume of Comparative Pathobiology under the subtitle of Invertebrate Models for Biomedical Research. This volume is the result. We hope that volume four will provide the reader further insight into the complexity and comprehensiveness of pathobiology. Pathobiology encompasses not only the study of pathologic conditions but also the biology of causative agents and response reactions.

Invertebrate pathology, like medical and veterinary pathology, for many years has been spearheaded by practical applications al though in more recent times many investigators have elected to focus their attention on basic mechanisms and the elucidation of basic phenomena. Although Elie Metachnikoff and Louis Pasteur may be considered the forerunners of invertebrate pathology, in modern times the late Edward A. Steinhaus and the late Arthur M. Heimpel, among others, must be considered the principal disciples. Con sequently, in recent years several symposia have been organized in honor of the memory of Steinhaus and Heimpel. When the proceedings of these occasions were examined and reviewed, it was decided that these could naturally be considered chapters of a single volume of Comparative Pathobiology under the subtitle selected. We wish to note that the chapters devoted to various aspects of Bacillus thuringiensis were originally presented at the thirteenth annual meeting of the Society for Invertebrate Pathology held in Seattle, Washington, on July 26 - August 2, 1980, under the title of the "Edward A. Steinhaus Memorial Symposium". This includes the contribution by Dr. Robert M. Faust on the professional contributions of Dr. Arthur M. Heimpel. Art, as he was known to his friends, was a founding member of the Society and later served as its president. The circle of his professional associates was international.

The study of parasites and their interactions with hosts continues to represent a challenging area of modern biology. The availability of new techniques and instrumentation, coupled with the development of daring new hypotheses and concepts, has paved the way for the dramatic evolution of parasitology from a static descriptive endeavor to a dynamic one based on biochemistry, immunology, molecular biology, and modern cell biology. Studies of this nature obviously fall within the domain of pathobiology. Consequently, when the contributions included in this volume of Comparative PathobioZogy were offered to this series. after critical review, we welcomed the opportunity to make them available to the scientific community. The contributions included herein represent presentations delivered before enthusiastic audiences at three different symposia, all held in 1983. The first, entitled "Some Aspects of Modern Parasitology," was organized by Dr. Gary E. Rodrick of the University of South Florida and myself on behalf of the American Society of Zoologists. The chapters by C. E. Carter and B. M. Wickwire. B. J. Bogitsh, and W. M. Kemp were originally presented at that symposium. The second symposium. organized by Dr. G. Balouet of the Faculte de Medecine, Brest, France, and myself on behalf, of the Society for Invertebrate Pathology, was entitled "Cellular Reactions in Invertebrates." The chapters by G. Balouet and M. Poder and M. Brehelin were originally presented at this symposium.