1. An Introduction to the Problem Operational Definitions A Survey of Animal Genitalia Genitalic Extravagance 2. Previous Hypotheses: Their Status to Date Lock and Key Genitalic Recognition Pleiotropism Mechanical Conflict of Interest Summary 3. Tests of the Lock and Key and Genitalic Recognition Hypotheses Lock and Key Species Isolation 4. Tests of the Other Hypotheses and a Summary Pleiotropism Arnold's Modification Mechanical Conflict of Interest Summary 5. Sexual Selection by Female Choice The Function of Copulation The Female Choice Hypothesis Effects of Female Choice on Genitalia Mechanical Fit of Genitalia Genitalia and Overall Male Fitness Major Evolutionary Patterns That Are Explained Relationships to Other Hypotheses 6. Male-Male Genitalic Genitalic Competition Sperm Displacement clasping Devices Male Adaptations That Short-cut Female Choice Topology of Female Reproductive Systems too Summary 7. Female Discretion after Genitalic Genitalic Contact Intromission Insemination Sperm Transport Sperm Destruction, Storage, and Activation Egg Maturation and Fetal Nourishment Oviposition Rate Tendency to Remate Summary 8. Remating by Females Strict Behavioral Monogamy Induced by Males Copulatory Plugs Antiaphrodisiacs Short-lived Females Monogamy in Termites Determining Remating Frequencies The Best Field Data on Remating Frequencies Heliconius Butterflies: A Test Case Sex Ratios and Sperm Exhaustion Summary 9. Apparent Contradictions of the Female Choice Hypothesis Interspecific Differences in Female Genitalia Lack of Species Specificity in Genitalia High Paternal Investment in Offspring Intraspecific Uniformity of Genitalia Spermatophore Complexity and Male-Female Contact Infrequency of Postcopulatory courtship Patterns of Genitalic change Summary 10. Use of Genitalia as Stimulators External Movements Intromission without Insemination Movements within the Female Indirect Evidence 11. specialized Nongenitalic Male Structures 12. Conclusions and an Overview References Index