CONTENTS. 



PART I. PAGE. 



Introduction 5 



Castration of Sebrights 6 



A male Sebright that did not become cock-feathered after castration 10 



Transitional feathers 10 



Castration of Fi hen-feathered males from Sebright by game 11 



Castration of Fz hen-feathered males 13 



Hewitt's Sebright hen that became cock-feathered in old age 14 



Heredity of hen-feathering 14 



Heredity of color in the cross between Sebright and Black-Breasted Game bantam. 17 



A. The Fi birds 18 



B. Description of F2 birds 19 



C. Back-cross of Fi to game 21 



D. The number of color factors involved 22 



E. Back-cross of Fi 9 to Sebright d" 23 



F. Review of the heredity of the color of the plumage in poultry 23 



Endocrine cells in ovary and testes of birds 32 



Luteal-cells in the testes of the male Sebright 34 



Endocrine cells in the testes of mammals 35 



Cyclical changes in the interstitial cells in hibernating mammals 36 



Hermaphroditism in poultry and the secondary sexual characters 37 



PART II. 



Darwin's theory of sexual selection 43 



Other theories to account for secondary sexual characters 45 



Display of the male 50 



PART III. 



The genetic and the operative evidence 62 



A. Evidence from mammals 64 



B. Evidence from birds 73 



C. Evidence from amphibia 86 



D. Evidence from crustaceans 89 



E. Evidence from insects 92 



PART IV. 



Summary and conclusions 95 



Bibliography 100 



Description of plates 106 



3 



