Front matter

THE GENETIC AND THE OPERATIVE EVIDENCE RELATING TO SECONDARY SEXUAL CHARACTERS

By T. H. Morgan 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.

Introduction5

Castration of Sebrights6

A male Sebright that did not become cock-feathered after castration10

Transitional feathers10

Castration of F₁ hen-feathered males from Sebright by game11

Castration of F₂ hen-feathered males13

Hewitt’s Sebright hen that became cock-feathered in old age14

Heredity of hen-feathering14

Heredity of color in the cross between Sebright and Black-Breasted Game bantam17

A. The F₁ birds18

B. Description of F₂ birds19

C. Back-cross of F₁ to game21

D. The number of color factors involved22

E. Back-cross of F₁ ♀ to Sebright ♂23

F. Review of the heredity of the color of the plumage in poultry23

Endocrine cells in ovary and testes of birds32

Luteal-cells in the testes of the male Sebright34

Endocrine cells in the testes of mammals35

Cyclical changes in the interstitial cells in hibernating mammals36

Hermaphroditism in poultry and the secondary sexual characters37

Part II.

Darwin’s theory of sexual selection43

Other theories to account for secondary sexual characters45

Display of the male50

Part III.

The genetic and the operative evidence62

A. Evidence from mammals64

B. Evidence from birds73

C. Evidence from amphibia86

D. Evidence from crustaceans89

E. Evidence from insects92

Part IV.

Summary and conclusions95

Bibliography100

Description of plates106

THE GENETIC AND THE OPERATIVE EVIDENCE RELATING TO SECONDARY SEXUAL CHARACTERS.

——— By T. H. Morgan ———