CONTENTS. 



PAGE. 



Introduction 5 



The material 7 



Juvenile characters 9 



The operation 10 



The anesthetic 10 



Preliminary steps 11 



Removal of testes 11 



Removal of ovary 12 



Description of cases 13 



Ducks 13 



Female ducks completely ovariotomized 14 



Female ducks partially ovariotomized 17 



Male ducks completely orchidotomized 18 



Male ducks partially orchidotomized 20 



Domestic fowl 21 



Female fowl completely ovariotomized 21 



Female fowl partially ovariotomized 25 



Male fowl partially or completely orchidotomized 26 



Age in relation to gonadectomy 31 



The age of the feather germ in relation to the type of feather developed 31 



Two types of females resulting from ovariotomy 34 



Effects of gonadectomy on particular parts of the body 36 



Effect on plumage 36 



Effect on head furnishings 36 



Effect on spurs 38 



Effects on the voice and associated organs 39 



Effect on the molt 39 



Effect on color of the mandible 41 



Effect on size 41 



Effect on behavior 42 



Effect on accessory organs of reproduction 42 



Effect on the bursa Fabricii 43 



Occurrence of characters of one sex in individuals of the opposite sex that are other- 

 wise normal 43 



Male characters in the otherwise normal female 43 



Female characters in the otherwise normal male 45 



Hen-feathered males 45 



Inheritance of secondary sexual characters 46 



Is the female bird a suppressed hermaphrodite? 47 



The relation between breeding and gonadectomy 48 



Darwin's and Wallace's theories of the origin of secondary sexual characters 49 



Nature and mode of the ovarian secretion 49 



Relation between the gonads and the secondary sexual characters in other groups .... 51 



Summary 51 



Literature cited 52 



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