The genetic and the operative evidence relating to secondary sexual characters

The author examines secondary sexual characters through breeding experiments and surgical operations, especially in poultry where some males show hen-like plumage. He reports castration and cross-breeding results, analyzes inheritance patterns of feathering and color, and correlates these with histological studies of endocrine cells in gonads. The work evaluates Darwin's theory of sexual selection alongside alternative explanations, surveys operative and genetic evidence across mammals, birds, amphibians, crustaceans, and insects, and integrates experimental and comparative data to assess hormonal versus selective origins of sex-linked traits, concluding with a synthesis of genetic and physiological mechanisms underlying secondary sexual characters.