This 1987 book reviews and illustrates the structure, as seen by the scanning and transmission electron microscopes, of the spermatozoa of insects, centipedes, millipedes and onychophorans. Virtually every reference in the large literature on sperm ultrastructure in these groups is cited and many further observations are included. The spermatozoa of spiders and other arachnids and crustaceans are also briefly treated. The remarkable diversity of sperm structure in arthropods is shown to have great value for the study of taxonomic and evolutionary relationships. These variations and omissions have important lessons for students familiar with the more orthodox sperm of mammals. Giant sperm reaching a length of 15mm, much longer than the male fly, are described for Drosophila and the genetic control of sperm structure and its manipulation by x-ray irradiation and hybridization, with implications for control of lepidopteran insect pests is discussed.