Insect hematology is a difficult and controversial subject. Developing suitable techniques to study hemocytes – their origin, development, differentiation, multiplication, and functions – has presented many problems; and the existing differences of opinion among insect hematologists on almost all aspects of insect hemocytes surely indicate the controversial nature of the subject. As a consequence, the study of insect hemocytes has not been popular, and this in turn has hindered progress in this area. Disagreement over the exact number of basic hemocyte types still remains, and I doubt if a consensus on this will ever be reached because this is largely a matter of opinion. Fortunately, however, insect hematologists recognize the existence of certain morphologically distinct hemocyte types, and there is a more or less general agreement on the names of these types. This has facilitated, to some degree, comparisons of various descriptions and has made it possible to define more accurately the physiological roles of at least some hemocyte types. Much of the physiological significance of hemocytes, however, remains to be understood, particularly their role in the insect endocrine system.

The book seeks no consensus on any aspect of hemocytes, but attempts to present a critical and, I hope, a balanced account of the subject as it is presently perceived by the contributors. Each contributor has had complete freedom to develop, interpret, and present his/her views on the subject. Portions of the chapters by Drs. Arnold, J. A. Hoffmann, Jones, Shapiro, and Sohi were presented at the XV International Congress of Entomology (1976) in a Special Interest Conference on Hemocytes.