Contributors.Preface.MAP Kinases in Mitogenesis and Development, J.E. Ferrell, Jr..The Role of the Epididymis in the Protection of Spermatozoa, B.T. Hinton, M.A. Palladino, D. Rudolph, Z.J. Lan, and J.C. Labus.Sperm Competition: Evolution and Mechanisms, T.R. Birkhead.The Cellular Basis of Sea Urchin Gastrulation, J. Hardin.Embryonic Stem Cells and in Vitro Muscle Development, R.K. Baker and G.E. Lyons.The Neuronal Centrosome as a Generator of Microtubules for the Axon, P.W. Bass.Index.