In retrospect, the range of topics covered in this monograph, although forming a coherent ensemble, is so extensive that a detailed discussion could easily extend to three or four times the current length. My approach has been to identify the critical issues, summarize the major accomplishments, and to suggest promising avenues for future research. To facilitate this sum mary presentation, I have limited the literature review largely to material published after 1970, extending to material appearing late in 1990. I gratefully acknowledge the advice of many colleagues, particularly the valuable criticisms of Drs. Warren Burggren, Joseph Kunkel, Randall Phillis, and John Stoffolano. I also wish to thank Mrs. Elizabeth Brooks for secretarial assistance. Finally, thanks are due to Dr. D. Czeschlik and his staff at Springer Verlag for their patience and support. Amherst, MA, October 1991 M. S. KAULENAS V Contents Chapter 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Chapter 2 The Reproductive Elferent Duct Systems and Associated Structures. Development and Genetic Control of Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. 1 Origin of the Germ Cells and Associated Cells and Tissues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. 2 Differentiation of the Efferent Duct System and Associated Structures . . . . . . . . . . . . . . . . . . . 9 2. 2. 1 The Male System . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2. 2. 2 The Female System . . . . . . . . . . . . . . . . . . . . . . . . . 13 2. 3 Genetic Control of Sexual Differentiation . . . . . 16 2. 3. 1 Daughterless. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2. 3. 2 Sex Determination: Measurement of the X:A Ratio. . . . . . . .. . . . . . . . . . . . . . . . . . 20 2. 3. 3 Sex Lethal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 2. 3. 4 Genes Controlling Somatic Sexual Differentiation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 2. 3. 5 Dosage Compensation . . . . . . . . . . . . . . . . . . . . .