Contents. List of Contributors. Preface (P.M. Wassarman). Y Chromosome Function in Mammalian Development (P.S. Burgoyne). A Super Family of Putative Developmental Signaling Molecules Related to the Protooncogene Wnt-1/int-1 (A.P. McMahon). Segmentation in Drosophila (K. Howard). Pattern Formation in Caenorhabditis Elegans (M. Han and P.W. Sternberg). Gap Junctional Communication During Mouse Development (N.B. Gilula, M.Nishi, and N. Kumar). Lens Differentiation and Oncogenesis in Transgenic Mice (H. Westphal). Subject Index.