Mechanisms of Gonadal Differentiation in Vertebrates. Preface and Introduction.- Evolution of Sex Chromosomes.- Evolution and Differentiation of Sex Chromosomes in Lower Vertebrates. With 8 Figures.- Evolution of Sex Chromosomes and Heterogametic Systems in Amphibia. With 7 Figures.- Aberrant Sex Chromosome Mechanisms in Mammals. Evolutionary Aspects. With 6 Figures.- Function of Sex Chromosomes.- Sex Chromosome Expression in Embryonic Development.- Expression of the 12E7 Antigen is Controlled Independently by Genes on the Human X and Y Chromosomes. With 1 Figure.- Chromosome Abnormalities and Gamete Production in Man.- Sex-specific DNA Sequences.- Sex Chromosome-Specific DNA Sequences.- Structure and Evolution of Human Y Chromosome DNA. With 7 Figures.- Evolutionary Conservation of Sex Specific DNA Sequences.- On Evolutionarily Conserved Simple Repetitive DNA Sequences: Do “Sex-Specific” Satellite Components Serve Any Sequence Dependent Function? With 4 Figures.- Morphological Aspects of Gonadal Differentiation.- Structural Aspects of Gonadal Differentiation in Mammals and Birds. With 15 Figures.- Morphogenesis and Fibronectin in Sexual Differentiation of Rat Embryonic Gonads. With 20 Figures.- Gonadal Sex Reversal.- The Peculiarities of Gonad Transformation in Teleosts.- Effects and Role of Estrogens in Avian Gonadal Differentiation. With 2 Figures.- Sex Reversal in the Mouse. With 4 Figures.- Morphogenetic Factors in Gonadal Differentiation.- Testicular Differentiation—a Developmental Cascade. Morphogenetic Effects of H-Y Antigen and Testosterone in the Male Mammalian Gonad. With 1 Figure.- X-linked Genes and Gonadal Differentiation.- H-Y Antigen in the Chicken. With 9 Figures.- H-Y Typing of Karyotypically Abnormal Mice.- On the Nature of H-Y Antigen. Concluding Remarks.