About 95 per cent of all known animal species are invertebrates. A knowledge of their sexual, reproductive, and development biology is essential for the effective management of species that are economically useful to man or are harmful to him, his crops, and livestock. This treatise is the first to cover all aspects of reproduction and development of the entire spectrum of invertebrates - terrestrial, marine, freshwater, brackish-water, free-living, and parasitic. The chapters, by leading world experts in their fields, are up-to-date and informative, and suggest a number of problems for future research. "Progress in Male Gamete Ultrastructure and Phylogeny" (issued in parts A- -C) is the ninth volume in the series. Contents Preface to the Progress Series, Preface to Volume IX, Part A, Contributors, Porifera, N. Boury-Esnault and B.G.M. Jamieson, Cnidaria and Ctenophora, Peter L. Harrison and B.G.M. Jamieson, Platyhelminthes, Nikki A. Watson, Nemertea, Å ke Franzé n and Bjö rn A. Afzelius, Rotifera, Giulio Melone and Marco Ferraguti, Gastrotricha, Maria Balsamo, Elena Fregni and Marco Ferraguti, Kinorhyncha, André y V. Adrianov and Vladimir V. Malakhov, Nematomorpha, Roberto Valvassori, Magda de Eguileor, Annalisa Grimaldi and Giulio Lanzavecchia, Acanthocephala, Marcella Carcupino and Bahram S. Dezfuli, Subject Index, Species Index.