Produced by Larry B. Harrison, Bryan Ness, Chuck Greif and the Online Distributed Proofreading Team at http://www.pgdp.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) THE GENETIC AND THE OPERATIVE EVIDENCE RELATING TO SECONDARY SEXUAL CHARACTERS BY T. H. MORGAN [Illustration: CARNEGIE INSTITUTION OF WASHINGTON 1902] PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON WASHINGTON, 1919 CARNEGIE INSTITUTION OF WASHINGTON PUBLICATION NO. 285 PRESS OF GIBSON BROTHERS, INC. WASHINGTON, D. C. CONTENTS. PART 1. PAGE. Introduction 5 Castration of Sebrights 6 A male Sebright that did not become cock-feathered after castration 10 Transitional feathers 10 Castration of F₁ hen-feathered males from Sebright by game 11 Castration of F₂ 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 F₁ birds 18 B. Description of F₂ birds 19 C. Back-cross of F₁ to game 21 D. The number of color factors involved 22 E. Back-cross of F₁ ♀ to Sebright ♂ 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.